United States Office of Research and EPAl625/R-921016 Environmental Protection Development June 1994 Agency Washington DC 20460 &EPA Radon Prevention in the Design and Construction of Schools and Other Large Buildings
Third Printing with Addendum, June 1994
ACTIVE OUTDOOR AIR SOIL DEPRESSURIZATION 5Y STEM
POSITIVE PRESSURE POSITIVE PRESSURE
POLYURETI-IANE SEALAN
GATIVE PRE 55URE NEGATIVE PRESSU EPA/625/R-92/016 June 1994
Radon Prevention in the Design and Construction of Schools and Other Large Buildings
Third Printing with Addendum, June 1994
Prepared by Kelly W. Leovic and A. 6. Craig
U.S. Environmental Protection Agency Air and Energy Engineering Research Laboratory Radon Mitigation Branch (MD-54) Research Triangle Park, NC 27711 Printed on RecycledPaper @ Notice
The U.S. EnvironmentalProtection Agency (EPA) strivesto provide accurate,com- plete, and useful information.However, neither EPA nor any personcontributing to the preparationof this documentmakes any warranty,expressed or implied, with respectto the usefulnessor effectivenessof any information, method, or process disclosed in this material.Nor doesEPA assumeany liability for, or for damagesarising from, the useof any information,method, or processin this document.Mention of firms, tradenames, or commercialproducts in this documentdoes not constituteendorsement or recommendation for use.
ii Contents
Notice ...... ii Figures...... V Tables...... V Abstract...... vi Metric ConversionFactors ...... Vii ... Acknowledgments...... Vlll
1. Introductionand Overview...... 1 1.1 Purpose...... 1 1.2 Scope and Content ...... 1 1.3 Radonand its Sources...... 2 1.3.1 Why is Radona Problem?...... 2 1.3.2 How RadonEnters a Building ...... 3 1.3.3 How to Determineif RadonPrevention is Needed...... 5 1.4 RadonPrevention Techniques ...... 6 1.4.1 Soil Depressurization...... 6 1.4.2 Building Pressurization...... 7 1.4.3 SealingRadon Entry Routes...... 8 1.5 Why RadonPrevention Should be Consideredin Building Design...... 9 2. TechnicalConstruction Information ...... 11 2.1 Active Soil Depressurization (ASD) ...... 11 2.1.1 ASD Designand Installation...... 12 2.1.1.1 Aggregate...... 12 2.1.1.2 SubslabWalls ...... 13 2.1.1.3 RadonSuction Pits ...... 13 2.1.1.4 RadonVent Pipe...... 16 2.1.1.5 SuctionFan ...... 19 2.1.1.6 SealingMajor RadonEntry Routes...... 20 2.1.2 Operationand Maintenance...... 20 2.1.2.1 Before Occupancy...... 22 2.1.2.2 Weekly...... 22 2.1.2.3 Annually ...... 22 2.1.3 Additional Instructionsfor Basements...... 22 2.1.4 Additional Instructionsfor Crawl Spaces...... 22 2.1.5 ASD Cost Estimates...... 24 2.1.6 Summaryof Guidelinesfor ASD Systems ...... 24
. . . III Contents (continued)
2.2 Building Pressurizationand Dilution ...... 24 2.2.1 DesignRecommendations for HVAC Systems...... 24 2.2.2 Standardsfor Ventilation ...... 26 2.2.3 Guidelinesfor Installationand Operation...... 26 2.2.4 Maintenance...... 26 2.2.5 Summaryof Building PressurizationGuidelines...... 27 2.3 SealingRadon Entry Routes...... 27 2.3.1 RecommendedSealants ...... 28 2.3.2 SealingConcrete Slabs...... 28 2.3.2.1 SlabJoints ...... 28 2.3.2.2 Slab Penetrationsand Openings...... 28 2.3.2.3 Crack Prevention...... 29 2.3.2.4 SubslabMembranes ...... 29 2.3.3 SealingBelow-Grade Walls ...... 29 2.3.3.1 Wall Types...... 29 2.3.3.2 Coatingsfor Below-GradeWalls ...... 30 2.3.4 SealingCrawl Spaces...... 31 2.3.5 Summaryof SealingRecommendations ...... 3 1 2.4 Guidelinesfor MeasuringRadon Levels...... 3 1
Appendix A: CaseStudy ...... 33 AppendixB: References...... 35 Appendix C: EPA RegionalOffices and Contacts...... 37 Addendum...... 38 IncreasingPressure Field Extensionby Modifying SubslabWalls ...... 38 ImprovedSuction Pits ...... 38
iv Figures
l-l Radondecay chart...... 2 l-2 Examplesof negativepressure sources in a typical building...... 3 l-3 Typical radonentry routesin slab-on-gradeconstruction...... 4 1-4a Typical radon entry routesin concreteblock basementwalls...... 4 I-4b Typical radonentry routesin pouredconcrete basement walls...... 5 l-5 Typical crawl spacefoundation entry routes...... 5 l-6 Subslabdepressurization theory...... 7
2-l Typical subslabdepressurization system...... 12 2-2a Interior footing/foundationwall...... 14 2-2b Thickenedslab footing...... 14 2-3a Outsidewalls and postload bearing...... 15 2-3b Interior walls betweenrooms and outsidewalls load bearing...... 16 2-3~ Hall and outsidewalls load bearing...... 17 2-3d All interior walls load bearing...... 18 2-4a Section1 (correspondsto Figures2-3a and b)...... 18 2-4b Section1 (correspondsto Figure 2-3~and d)...... 19 2-5 Radonsuction pit...... 20 2-6 Sealingpipe penetrationsthrough roof...... 21 2-7 Submembranedepressurization in crawl space...... 23 .2-8 Building positivepressurization with HVAC system...... 25 2-9 Exampleof building depressurizationwith HVAC system...... 26 2-10 Every other interior wall block is turnedon its side to allow soil gas to passthrough...... 39 2-11 Interior CMU wall ...... 39 2-12 Revisedsubslab suction pit...... 40 2-13 Smallersubslab suction pit ...... 40
Tables
2-l EstimatedCosts for Primary ASD Components...... 24 2-2 Examplesof OutdoorAir Requirementsfor Ventilation in CommercialFacilities ...... 27
A-l Cost of Mitigation Systemin JohnsonCity Hospital...... 34 Abstract
It is typically easierand much lessexpensive to designand constructa new building with radon-resistantand/or easy-to-mitigatefeatures, than to add thesefeatures after the building is completedand occupied.Therefore, when building in an areawith the potential for elevatedradon levels, architectsand engineersshould use a combinationof radon prevention construction techniques.To determineif your building site is located in a radon-pronearea, consult your EPA RegionalOffice or stateor local radiationoffice. We recommendthe following three radon preventiontechniques for constructionof schoolsand other large buildings in radon-proneareas: (1) install an activesoil depressur- ization (ASD) system,(2) pressurizethe building using the heating,ventilating, and air- conditioning (HVAC) system, and (3) seal major radon entry routes. Specific guidelines on how to incorporatethese radon preventionfeatures in the designand constructionof schoolsand other large buildings are detailedin this manual. Chapter 1 of this manual is a generalintroduction for those who need background information on the indoor radon problemand the techniquescurrently being studiedand applied for radon prevention. The level of detail is aimed at developing the reader’s understandingof underlying principlesand might best be usedby school officials or by architectsand engineerswho needa basicintroduction. Chapter 2 of this manual provides comprehensiveinformation, instructions, and guidelines about the topics and constructiontechniques discussed in Chapter 1. The sectionsin Chapter 2 contain much more technicaldetail and may be best used by the architects,engineers, and buildersresponsible for the specificconstruction details.
vi Metric Conversion Factors
Although it is EPA policy to usemetric units in its documents,non-metric units have been used in this report to be consistentwith commonpractice in the radon mitigation field Readersmay refer to the following conversionfactors as needed. Non-Metric Times YieldsMetric cubic foot (ft’) 28.3 liters (L) cubic foot per minute (fP/m) 0.47 liter per second(L/s) foot (ft) 0.305 meter(m) gallon (gal.) 3.79 liters (L) horsepower(hp) 746 watts (WI inch (in.) 2.54 centimeters(cm) inch of water column (in. WC) 248.9 pas&s (Pa) mil (0.001 in.) 25.4 micrometers(pm) picocurieper liter (pCi/L) 37 becquerelsper cubic meter(Bq/m’) pound per squareinch (psi) 6894.8 pa=aB (Pa) squarefoot (ft’) 0.093 squaremeter (m*)
vii Acknowledgments
The information containedin this technical documentis basedlargely on research conductedby the Air and Energy EngineeringResearch Laboratory (AEERL) of the EnvironmentalProtection Agency’s (EPA’s) Office of Researchand Development. W.A. Turner of the H.L. Turner Group and T. Brennan of CamrodenAssociates preparedthe initial draft of the documentin 1991 undercontract number OD2009NCSA. ScottR. Spiezleof SpiezleArchitectural Group prepared the figuresunder contract number 68-DO-0097. Technical writing services were provided by the Kelton Group under contractnumber 2D0682NASA. Drafts of this documenthave been reviewed by a large numberof individualsin the governmentand in the private and academicsectors. Comments from thesereviewers in addition to thosefrom the individualslisted abovehave helped significantly to improvethe completeness,accuracy, and clarity of the document.The following reviewersoffered input: William Angel1of MidwestUniversities Radon Consortium; Timothy M. Dyessand D. Bruce Henschelof EPA’s AEERL; DeaneE. Evans of AJA/ACSA Joint Council on ArchitecturalResearch; Kenneth Gadsby of PrincetonUniversity; Patrick Holmesof the Kentucky Division of CommunitySafety: Norman Grant of Quoin Architectsand Engi- neers:Gene Fisher, Jed Harrison,Dave Murane, Dave Price, and Brian Ligman of EPA’s Office of Radiation Programs;Clifford Phillips of Fairfax County Pubic Schools;Steve Sandersof Auburn University; Dave Saumof INFILTEC; Arthur E. Wheelerof Wheeler EngineeringCo.; LarraineKohler of EPA Region2; Bill Bellangerof EPA Region3; Steve Chambersof EPA Region7; Phil Nyberg of EPA Region 8; Michael Bandrowskiof EPA Region 9; Kevin Teichman of EPA’s Office of Technology Transfer and Regulatory Support; Ruth Robenolt of EPA’s Office of Communications;Jerry L. Clement of EducationalFacilities in Houston,TX; and ThomasE. Toricelli of T.E. Toricelli AIA Architects.
. . VIII Chapter 1
Introduction and Overview
1.1 Purpose who needa basic introduction to radon and radon reduction Radonis a naturallyoccurring radioactive gas in ambient techniques.Those who are alreadyfamiliar with theproblems air. It can also accumulatein varying amountsin encIosed of constructing radon-resistantbuildings should go on to buildings. Radon is estimatedto causemany thousandsof Chapter2. Chapter 1 containsthe following sections: lung c 1 construction well below the currently recommendedEPA releasedin the form of radiation.This radiationconstitutes the action level of 4 pCi/L and as close to the long-term national healthhazard to humans. goal of ambientradon levels(0.4 pCi/L) as possible.Many of theseradon preventiontechniques will eventuallyprove to be Whenradon and radon decayproducts are presentin the transferableto the architect’s and engineer’scommon prac- air, somewill be inhaled.Because the decayproducts are not tices and, it is hoped, will be adopted in national building gases,they will stick to lung tissueor largerairborne particles codes by the model building code organizations.EPA is that later lodge in the lungs. The radiation releasedby the currently working with the American Society of Testingand decay of these isotopes can damage lung tissue and can Materials(ASTM) to developa standardfor radonprevention increaseone’s risk of developinglung cancer.The healthrisk in the constructionof large buildings. dependson how long and at what levelsa personis exposedto radon decayproducts. Radon and radon decayproducts cause 1.3 Radon and its Sources thousandsof deathsper year in the United States(1). The following subsectionsanswer three basic questions Like otherenvironmental pollutants, there is someuncer- that many peoplehave about radon: tainty aboutthe magnitudeof radon healthrisks. However,we 1) Why is radon a problem? know more about radon risks than the risks from most other cancer-causingsubstances. This is becauseestimates of radon 2) How doesradon enter a building? risks are basedon the studies of cancer in humans(under- ground miners). Additional studiesof more typical popula- 3) How should one evaluatea constructionsite? tions are underway. Smoking combined with exposureto 1.3.1 Why is Radon a Problem? elevatedlevels of radon is an especiallyserious health risk. Radon is a colorless,odorless, radioactive gas produced Children have been reported to have greaterrisk than by the radioactivedecay of radium-226,an elementfound in adults of certaintypes of cancerfrom radiation,but thereare varying concentrationsin many soils and bedrock.Figure 1-l currentlyno conclusivedata on whetherchildren are at greater showsthe seriesof elementsthat begin with uranium-238and risk thanadults from radon. eventuallydecay to lead-210.Of all theelements and isotopes Radonlevels are usually measuredin picocuriesper liter in the decay chain, radon is the only gas.Because radon is a of air @G/L). Currently, it is recommendedthat indoor gas,it can easily movethrough small spacesbetween particles radon levels be reduced to less than 4 pCi/L. But the lower of soil and thusenter a building. Radoncan entera building as the radon level, the lower the health risk: therefore,radon a component of the soil gas and reach levels many times levels should be reduced to as close to ambient levels as higher thanoutdoor levels. feasible (0.4 pCi/L). For additional information on the esti- While many of the isotopes in the uranium-238decay matedhealth risks from exposureto variouslevels of radon, seriesexist for a long time beforethey decay, radon has a half- refer to EPA’s A Citizen’sGuide IO Radon, Second Edition (1). life of only 3.8 days.Radon decay products have even shorter Architectsand engineersshould consider the healthrisks half-lives than radon and decay within an hour to relatively of radon prior to constructing new buildings or renovating stablelead-210. At eachlevel of this decayprocess, energy is existing buildings in radon-proneareas. Including radon pre- Lead 19.4 l-7 Figure l-l. Radon decay chart. Time shown in half-life. 2 vention techniquesduring building design and construction entry. Sourcesof negativepressure in a typical building are will reduce the chance that a building will have a radon shown in Figure 1-2. problem and also reducethe cost of reducingradon levels,if needed. Other Ways Radon Enters a Building 1.32 How Radon Enters a Building Radon also can enter buildings when there are no pres- sure differences. This type of radon movement is called The most commonway for radon to enter a building is diffusion-driventransport. Diffusion is the samemechanism from the soil gas through pressure-driventransport. Radon that causesa drop of food coloring placed in a glassof water can also enter a building through diffusion, well water, and to spreadthrough the entire glass.Diffusion-driven transport constructionmaterials. These modes of radon entry arebriefly is rarely the causeof elevatedradon levels in existing build- explainedbelow. ings. It is also highly unlikely that diffusion contributessig- nificantly to elevatedradon levels in schoolsand other large Pressure-Driven Transport buildings. Radoncan enter a building throughpressure-driven trans- Another way radon can enter a building is through well port only if all of the following four conditionsexist: water. In certain areas of the country, well water that is 1) a sourceof radium to produceradon supplied directly to a building and that is in contact with radium-bearingformations can be a source of radon in a 2) a pathway from the sourceto the building building. At this writing, the only known health risk associ- atedwith exposureto radon in water is the airborneradon that 3) an openingin the building to permit radon to enterthe is releasedfrom the water when it is used.A generalrule for building housesis that 10,000 pCi/L of radon in water contributes 4) a driving force to moveradon from the sourceinto the approximately1 pCi/L to airborneradon levels.It is unlikely building throughthe opening that municipal water suppliedfrom a surfacereservoir would containelevated levels of radon and,thus, buildings using this Pressure-driventransport is the mostcommon way radon sourceof water should not need to conduct radon testingof enters a building. Pressure-driventransport occurs when a the water. lower indoor air pressuredraws air from the soil or bedrock into the building. This transporthappens in many schoolsand Radon can also emanatefrom building materials.How- other large buildings becausethese buildings usually operate ever, this has rarely been found to be the causeof elevated at an inside air pressurelower than that of the surrounding levelsin existingschools and other largebuildings. The extent soil. Negative pressure inside buildings is due in part to of the use of radium-contaminatedbuilding materialsis un- building shell effects.For example,indoor/outdoor tempem- known but is generallybelieved to be very small. ture differences,wind, and air leaksin the shellof thebuilding Becausepressure-driven transport is by far the most can contribute to negative pressuresin the building. The commonway radon enters a building. this manual dots not design and operationof mechanicalventilation systemsthat addressthe other ways that radon can enter a building. depressurizethe building can also greatly influence radon Kitchen Range Exhaust Fan Roof Exhaust Fan - Positive Pressure @= Negative Pressure Figure 1-2. Examples of negative pressure sources In a typical buildlng. 3 Radon Entry and Substructure Type strutted today are slab-on-gradesubstructures, Section 2.1 of this manual emphasizesradon preventionfor slab-on-grade Elevatedlevels of radoncan occur in any building regard- buildings.However, many of the radonprevention techniques less of foundation type. Figures 1-3, l-4, and l-5 show used for slab-on-gradesubstructures are also applicable to commonradon entry routesfor buildings constructedon slab- basementsand crawl spaces. on-grade, basement,and crawl space foundations, respec- tively. Becausea large majority of the new buildings con- Wall Cracks and Form Ties Plumbing Pipe Floor Joist \ Floor Joints/Cracks Concrete Floor Slab 11 Perimeter Poured Concrete Wall Poured Q= Positive Pressure c3 = Negative Pressure Figure 1-3. Typical radon entry routes in slab-on-grade constructlon. Soil Gas/Radon Movement through Hollow Core Block Plumbing Pipe CL-.,.. L-.ic.* \lT \ Wall Joints/Cracks Floor Joints/Cracks Concrete Floor Slab Concrete Block Wall Concrete Block Wall 0+ = Positive Pressure @ = Negative Pressure Flgure l-4a. Typical radon entry routes in concrete block basement walls. 4 Wall Cracks and Form Ties Plumbing Pipe Floor Joist Joints/Cracks 7 r Concrete Floor Slab 11 Perimeter _ ,. Poured Concrete Wall Poured Concrete Wall 0 I Positive Pressure e = Negative Pressure Figure Mb. Typical radon entry routes in poumd concrete basement wsiis. 7 Wall Penetration Floor Penetration Plumbing Penetration 4, “I”. I I Earth Floor z Positive Pressure 0 = Negative Pressure Figure i-5. Typical crawl space foundation entry routes. The specific additional requirementsfor basementsub- soils at a building site with subsequentindoor radon levels structures(such as sealingof basementwalls) are discussedin containedin a building built on that site. Bedrock and soils Section2.1.3. The additionalrecommended requirements for interactin complexways with dynamicbuilding behaviorand crawl spacesare discussedin Section 2.1.4 (submembrane environmentalfactors. There are too many combinationsof depressurization). factors that causeelevated indoor radon concentrationsfor simplecorrelations to exist. 1.3.3 How to Determine if Radon Prevention is Needed In the absenceof a simple test to determinewhen radon preventiontechniques are needed,the discussionbelow cov- An often-askedquestion is “Can one determineifradon- ers various sourcesof information to assist architectsand resistant construction techniquesare necessaryfor a given engineerswith site assessment. site?” A simple and inexpensivestandardized test that could conclusivelyidentify problem siteswould be very helpful. At EPA National Radon Potential Map presentthere are no reliable, easily applied, and inexpensive methodsfor correlatingthe resultsof radonevaluation tests of One sourceof guidanceis the growing body of radondata availableat local, state,and regional levels.With thesedata, 5 EPA is compiling a National RadonPotential Map. The map building budgetwill probably be muchless than $1.OO per ft2 integratesfive factorsto produceestimates of radonpotential. of earthcontact floor areain mostparts of the country. In most Thesefactors are indoor radon screeningmeasurements, geol- cases (buildings that are already designed to have subslab ogy, soil permeability, aerial radioactivity, and substructure aggregateand plastic vapor retarder), sealing major radon type. All relevantdata were collected and carefully evaluated entry routesand installing an ASD systemwill add less than so that the five factorscould be quantitativelyranked for their $0.10 - $0.20 per ft2 of earth contact floor area to total costs. respective“contribution” to the radon potential of a given Therefore,it is often more cost-effectiveto build using radon area.The mapassigns every county of the U.S. to one of three preventiontechniques, rather thanwaiting until thebuilding is radon zones. Zone 1 areas have the highest potential for completedand then having to add a radon mitigation system. elevatedlevels, Zone 2 areasalso havepotential for eievated indoor radon levels but the occurrenceis more variable,and 1.4 Radon Prevention Techniques Zone 3 areashave the leastpotential for elevatedlevels. Like most other indoor air contaminants,radon can best The radon potential estimatesassigned on the map are be controlled by keeping it out of the building in the first statedin termsof predictedaverage screening levels. They are place,rather thanremoving it onceit hasentered. The follow- not intended to predict annual averagemeasurements, but ing subsectionsbriefly describethe recommendedradon pre- rather to assessthe relative severity of the potential for vention techniquesdiscussed in Chapter2 of this manual: elevatedindoor radon levels. We recommendyou use this 1.4.1 Soil Depressurization. A suction fan is usedto mapwhen it becomesavailable to help determinewhen radon producea low-pressurefield underthe slab.T%is preventionconstruction techniques might be needed. low-pressurefield preventsradon entry by caus- Radon Levels in Nearby Buildings ing air to flow from the building into the soil. 1.4.2 Building Pressurization. Indoor/subslabpres- Radon levels in a sampleof existing U.S. schoolbuild- sure relationshipsare controlled to preventra- ings were recently surveyedby EPA. Measurementsto date don entry. More outdoor air is supplied than indicatethat many schoolsand other large buildings through- exhausted so that the building is slightly pres- out the country have rooms or classroomswith radon levels surized compared to bolh Ihe exterior of the above4 pCi/L. Many havebeen measuredat levelsin excess building and the subslabarea. of 20 pCi/L. It is expectedthat the geographicdis!ribution of the radonproblem in schoolsand other largebuildings will be 1.4.3 SealingRadon Entry Routes.Seal major radon similar to that for homes.You can contact regional, state,or entry routes to block or minimize radon entry. local officials for information about radon levels in nearby buildings and usethis information,together with the National These radon prevention techniquesare relatively inex- Radon Potential Map, to help decide if you are in a radon- pensiveand easy to install. WC recommendthat all three of prone area. thesetechniques be usedin new constructionto ensuremaxi- mum radon control. Soil 1.4. I Soil Depressurization Severalstudies have attemptedto make simple correla- The most effectiveand frequently used radon-reduction tions betweenradon or radium concentrationsin the soil and techniquein existingbuildings is activesoil depressurization indoor radon concentrations.No direct correlationshave been found. (ASD). Building Materials How an ASD System Works An ASD systemcreates a low-pressurezone beneaththe An extremely small percentageof U.S. buildings with slab by using a powered fan to create a negative pressure indoor radon concentrationsgreater than 4 pCi/L can be beneaththe slab and foundation.This low-pressurefield pre- attributedto building materials.Most of the building material ventssoil gas from entering Lhebuilding becauseit reverses problems have arisen from the use of known radium-rich the normaldirection of airflow where the slab and foundation wastessuch as aggregatein block or in fill around and under meet. If the low pressurezone is extended throughout the houses, or in areasof buildings with no ventilation.None of the existing large buildings studiedin EPA’s Air and Energy entire subslabarea, air will flow from the building into the soil, effectively sealingslab and foundationcracks and holes Engineering ResearchLaboratory’s researchprogram have (2). For a simplified view of the operating principle of an had any identifiable problem associatedwith radon from ASD, refer to Figure l-6. A similar systemwithout a fan for building materials.However, be awarethat building materials “activation’*is referredto asa “Rough-in” of an ASD system, are a potential problem. But unlessbuilding materialshave been identified as radium-rich in that region of the country, and is briefly discussedat the end of this section. the chanceof obtaining significantradon levelsfrom building The following are essentialinstructions for the design materialsis very small. and constructionof a soil depressurizationsystem: Summary . Place a clean layer of coarse aggregateof narrow particle size distribution (naturallyoccurring gravel or Basedon currentresearch and the additionalcost of radon crushedbedrock) beneath the slab. resistantconstruction features, the expectedimpact on the DepressurizationFan J Subslab DepressurizationSystem creates low pressure zone beneath the slab. This prevents radon-containingsoil gas from Higher Air Pressure entering the building by changing the direction of airflow. Air exhausted from under the s&b is released above the roof where the elevatedradon levels can dilute into the atmosphere. Low Air Pressure Radon Suction Pit 0 = Positive Pressure 0 I Negative Pressure Figure l-6. Subslab depressurkatlon theory. . Eliminateall majorbarriers to extensionof the subslab ings can easily overcomea passivesystem. Also, the large low pressurezone, such as interior subslabwalls. number of radon suction pits and vent pipes needed for passivesystems to be effectivein a largebuilding would make . Install radon suction pit(s) beneath the slab in the installationmore expensivethan an ASD system.Therefore, aggregate(one radon suction pit for each area sepa- in radon-proneareas we recommendyou do not usepassive rated by subslabwalls). soil depressurizationsystems. We do recommend,as a mini- . Install a vent stackfrom the radon suctionpit(s) under mum,that the designfeatures for an ASD systembe roughed- the slab to the roof. in for later activationif needed. . Install a suctionfan on the vent stack.(The fan should ASD Costs be operatedcontinuously, and the systemshould be Severalfactors affect the cost of an activesoil depressur- equipped with a warning device to indicate loss of ization system.Incremental installation costs for a system negativepressure through fan failure or other causes.) designedinto a new largebuilding rangefrom aslow as $0.10 . Sealall major slab and foundationpenetrations. per ft2 of earth contact area to more than $0.75 per ft2, dependingon the availability of aggregateand sealingcosts Rough-in for an ASD System (3,4,5,6,7,8). If aggregateis aheadypart of the design,the costswill be at the low end. Incorporationof the aggregate A rough-in for an ASD systemis the sameas an ASD and vapor retarder is consideredgood architecturalpractice systemexcept there is no fan. For new constructionwhere and is required by code in most areas of the U.S., and, radonlevels are elevatedeven marginally, the installationof a thereforewould not be considereda radon-preventioncost. rough-in systemis a prudentinvestment and is recommended. If a building is found to havea radonproblem, then a rough-in For comparison,a recent EEA survey showed that the can easily be convertedinto an ASD systemby installing a averagecost for installing ASD in an existing schoolis about fan. $0.50per ft* (9). Thesecosts could rangefrom about$0.10 up to $3.00 per ft* of earth contact floor area dependingon the Passive Soil Depressurization structureand subslabmaterials. Architectsand engineersmay ask,“Is it possibleto install 1.4.2 Building Pressurization a soil depressurizationsystem that works passively(that is, without a fan)?” Although researchhas shown that passive Building pressurizationinvolves bringing in more air to systemsare sometimeseffective in home construction,they the building than is exhausted,causing a slightly positive are not recommendedfor use in schools and other large pressureinside the building relative to the subslabarea. The buildings. Many competingnegative pressures in large build- positivepressure in the building causesair to flow from inside thebuilding to the outdoorsthrough openings in the substruc- ture and building shell; this effectively seals radon entry Onceradon hasentered a building, anotherway to reduce routes.Building pressurizationis similar to ASD in that both radon levels is by diluting them with ventilation air (outdoor methodsblock radon entry routes using air pressurebarriers: air). Dilution air should be supplied from outdoorsin accor- but the systemsare different in that, with building pressuriza- dancewith ASHRAE Standard62-1989 (10). To reducehighly tion, air is pushedout of the building from insiderather than elevatedradon levels it may be necessaryto supply higher being drawn out from under the slab, as in ASD. The follow- quantitiesof outdoorair thanthose recommended by ASHRAE. ing sectionexplains the principles of building pressurization (Note that neitherpressurization nor dilution is effectivewhen using the heating, ventilating, and air-conditioning (HVAC) the HVAC systemis not operating,such as in night and week systems. end setback.)Additionally, dilution is not an effectivestand- alone radon reduction techniqueif radon levels are substan- How Buildings Typically Operate tially elevated.Dilution is a lessreliable and frequentlymore Many buildings (both leaky and tight buildings) tend to costly approachthan the otherradon preventiontechniques. maintainan indoor air pressurelower thanoutdoors. It is often In summary, building pressurization with the HVAC difficult to continuouslyoperate a building to obtain slightly system can reduce radon levels; however, becauseof the positivepressure conditions unlessthe building shell is tight difficulty of properly operating the system in a way that and the building HVAC systemsupplies more outdoor air to continuouslyprevents radon entry, building pressurizationis each room than is exhausted.This difficulty is due to a not recommendedfor use as a stand-aloneradon-control complexinteraction between the building shell, the mechani- system in new buildings. When building pressurizationis cal systems,the building occupants,and the climate. used with the other methodsof radon prevention(ASD and Modem buildings generally are constructedwith fan- sealingof major radon entry routes),building pressurization powered HVAC systemsto provide outdoor air to the occu- contributesto low radon levels. pants. Many buildings also have exhaust fans to remove Costsand savingsfor HVAC systemsand a tight building internally generatedpollutants from the building. If the sys- shell are not presentedbecause they are consideredgood tems place the earth contact area under a slightly positive architectural and engineering practice, and moreover,are pressurewith respectto the subslab,they will preventradon mandatedby many building and energycodes. entry and will dilute radon under the slab for as long as the systemsare operating. However, if these fan systems(by 7.4.3 Sealing Radon Entry Routes design, installation, maintenance,or adjustment)place any Becausethe greatestsource of indoor radon is almost earth contact area of the building under a negativepressure always radon-containing soil gas that enters the building with respectto the soil, radon can enterthrough any openings through cracks and openingsin the slab and substructure,a in the slab. good place to begin when building a radon-resistantbuilding Important Features of HVAC Systemsto Prevent Radon is to make the slab and substructureas radon-resistantas Entry economicallyfeasible. The following HVAC systemfeatures and operating guide- However, it is difficult, if not impossible,to seal every lines shouldbe followed for radon prevention: crack and penetration.Therefore, sealing radon entry routes and constructingphysical barriersas a stand-aloneapproach . In radon-proneareas, eliminate air supply and return for radon control in schoolsand other large buildings, is not ductwork locatedbeneath a slab,in a basement,or in a currently recommended.On the other hand, sealingof major crawl space in accordancewith ASHRAE Standard radon entry routes will help reduceradon levelsand will also 62-1989 (10). greatly increasethe effectivenessof other radon prevention techniques.For example,sealing increasesthe effectiveness . Supply outdoor air in accordancewith guidelinesin of ASD by improving thepressure field extensionbeneath the ASHRAE Standard62-1989 (10). slab. Sealingalso helps to achievebuilding pressurizationby . Constructa “tight” building shell to facilitate achiev- ensuringthat the building is a “tight box” without air leakage. ing a slightly positive pressurein the building. Many of thesesealing techniques are standardgood conslruc- tion practices. . Sealslab, wall, and foundationentry pointsas noted in Section1.4.3, especially in areasof thebuilding planned Sealing Recommendations to be under negative pressure by design (such as Radonentry routes that shouldbe sealedare: restrooms,janitor’s closets,laboratories, storage clos- ets, gymnasiums,shops, kitchen areas). Floor/wall crack and other expansionjoints. Where codepermits, replace expansion joints with pour joints . Ensure proper training and retraining of the HVAC and/or control sawjoints becausethey are moreeasily systemoperators, together with an adequatebudget, so and effectivelysealed. that the system is properly operatedand maintained. (This appearsto be a major areaof neglectin existing Areasaround all piping systemsthat penetratethe slab schoolbuildings.) or foundationwalls below grade(utility trenches,elcc- trical conduits,plumbing penetrations,etc.). . In areaswith large exhaustfans, supply more outdoor air than air exhaustedif possible. Masonrybasement walls. 8 Limitations of Sealing . Poor communicationbelow the floor slab (i.e., no aggregateor aggregatewith many fines or with wide Many constructionmaterials are effective air and water particle size distribution range). barriers and also retard the transferof radon-containingsoil gas.In practicehowever, the difficulties that arisewhen using . Barriers to subslabcommunication (internal subslab sealingand physical barrier techniquesas the only meansof walls). control are virtually insurmountable.Physical barriers have . proven to be frequently damagedduring installation; more Radonentry points at expansionand control joints. over, failure to seal a single opening can negatethe entire . Easeof running the radon vent pipe and power source effort, especiallywhen radon concentrationsare high. Never- throughand/or out onto the building’s roof. theless,you should seal major radon entry routes: not only will sealingretard radon transferbut sealingwill also increase . Building depressurizationcaused by the I-WAC sys- the effectivenessof ASD and building pressurization. tem (or other fans) exhaustingmore air than is sup- plied. The cost of sealingmajor radonentry routesis dependent on the building design and local constructionpractices. For All of the above factors can be controlled in new con- one example,refer to the casestudy in AppendixA. struction.As further researchis conducted,additional infor- mationon the radonprevention features, or betterguidance on 1.5 Why Radon Prevenfion Should be when they arenot needed,should become more clear and will Considered in Bullding Design be documentedin future updatesof this manual. Most of the radon preventiontechniques covered in this Again, we emphasize that it is important to include manualcan be applied to existing buildings, but installation radon prevention features during design. Including these will cost more than if thesetechniques were installedduring features during building construction makes their appli- initial construction. For example, factors that increasethe cation easier and costsmuch less than adding them after difficulty and cost to install an ASD system in an existing the building is completed. building include: Chapter 2 Technical Construction Information As outlined in Chapter 1, there are three practical and Principles of Operation cost-effectiveapproaches to preventingelevated radon levels in new buildings. An ASD systemprevents radon entry by creatinga nega- tive-pressurezone beneaththe slab. If the negative-pressure . Active Soil Depressurization(Section 2.1) zone is extendedthroughout the entire subslabarea, air will . flow from the building into the soil, effectively sealingslab Building Pressurization(Section 2.2) and foundationcracks and holes,and thuspreventing the entry . SealingRadon Entry Routes(Section 2.3) of radon-containingsoil gas. Figure 2-l illustratesa typical ASD system. EPA recommendsusing all three of these methodsto ensureeffective and reliable radon control. To createthis negative-pressurezone, a radon suctionpit is installedin the aggregateunder the slab.This subslabpit is The following three sectionspresent detailed technical then connectedto a vent pipe that runs from the pit to the information for implementingthe above approaches.These outdoors.A suctionfan is connectedto the pipe outsideof the sectionsmight best be used by the architectsand engineers building to produce the negative-pressurezone beneaththe who are developingthe specificationsand constructiondraw- slab, hencethe systemis “active.” A lower air pressurein a ings for the building, and by the contractorwho is building the building relative to the surroundingsoil is what drawsradon- structure.Guidelines for conductingradon measurementsin containingsoil gasinto a building. The ASD systemreverses schools ‘and other large buildings are briefly discussedin the pressuredifference -and thusthe airflow directionat the Section2.4. slab - causing the subslabpressure to be lower than the indoor pressure.This air pressuredifferential keepsradon- 2.1 Active Soil Depressurization (ASD) containingsoil gasfrom enteringthe building. This sectiondescribes how to design,install, and main- kti an ASD system.The discussionpertains to slab-on-grade This manual describesthe design and installation of a substructuressince most new schoolsand other large build- completeASD system.A soil depressurizationsystem could ings are constructedslab-on-grade. Guidelines for basement also be “roughed-in” and activatedwith a fan later, if needed. substructuresare similar to slab-on-gradebuildings, except For new construction,where radon levelsmay be evenmar- that basementwalls add anotherpotential radon entry point ginally elevated,the installation of a rough-in systemis a that must be sealed.The application of ASD to basementsis prudent investmentand is recommended.If the completed briefly coveredin Section2.1.3. Radon control in buildings building hasa radonproblem, then the roughed-insoil depres- with crawl spacesubstructures is addressedin Section2.1.4. surizationsystem can easily be madeactive at a low cost by adding a fan. In mostparts of the U.S., designand constructionof new buildings with ASD systemsis relatively easyand cost effec- Architectsand engineers may ask,“Is it possibleto inskdl tive. Incorporating an ASD system into a new building is a soil depressurizationsystem that works passively(that is, highly recommendedin radon-prone areas, since effective without a fan)?” Although researchhas shown that passive operationof an ASD systemis dependenton building design systemsare sometimeseffective in home construction,they factors.Although it is possibleto add an ASD systemafter the are not recommendedfor use in schools and other large building is complete,the cost and effectivenessof the system buildings.Many competingnegative pressures in large build- will be directly influencedby building designparameters that ings can easily overcomea passivesystem. Also, the large can be easily controlledduring building designand construc- number of radon suction pits and vent pipes needed for tion. Certain parameters,such as aggregateselection and passivesystems to be effectivein a largebuilding would m‘ake subslabwalls, cannot be practically modified in an existing installationmore expensivethan an ASD system.Therefore, building. in radon-proneareas we recommendyou do not usepassive soil depressurizationsystems. We do recommend,as a mini- mum, that the designfeatures for an ASD systemshould be roughed-mfor later activationif needed. 11 Radon Exhaust Fan Roof Exhaust Fan Radon Exhaust Stack Note: Seal All Major Slab Openings, Radon Vent Pipe Cracks, or Penetrations . Schedule 40 PVC Polyurethane Sealant Radon Suction Pit ASTM Size #5 Aggregate or Equivalent 6= Positive Pressure @ = NegativePressure Figure 2-l. Typical subslab depressurlzation system. Not to scale. 2.1.1 ASD Design and Installation 2.1 .l .l Aggregate The six essentialguidelines for designingand installing Figure 2-l illustrateshow the creationand extensionof a ASD systemsin schoolsand other large buildings are listed negativepressure field beneaththe slab will causeair to flow below. The designand constructionprocedures for each are from the building into the subslab area. This direction of discussedin detail in the sectionsthat follow. airflow will prevent entry of soil gas into the building. The radon-containingsoil gas is drawn up the vent pipe and 1) Place a continuous4- to 6-m. layer of clean, coarse exhaustedoutdoors where it will be quickly diluted to ambient aggregateunder the slab.(Aggregate, Section 2.1.1.1) levels. 2) Eliminate barriers to subslabairflow such as subslab To extendthis negativepressure field effectively,highly walls. (SubslabWalls, Section2.1.1.2) permeablematerial, such as aggregate, should be placedunder the slab.If the subslabmaterial has low permeability(such as 3) Install a 4- by 4-ft areaby 8-m. deepradon suctionpit (or equivalent)under the slab. (Suction Pits, Section tightly packed sand or clay), or is interrupted by interior 2.1.1.3) subslabwalls (as discussedin Section2.1.1.2), the pressure field might not extend to all areasof the soil under the slab. 4) Run a 6-m. diameterPVC radon vent pipe from the The building should be designedso that the pressurefield radon suction pit to the outdoors.(Radon Vent Pipe, extendsunder the entire building. To ensurethe properexten- Section2.1.1.4) sion of the pressurefield, install a 4- to 6-m. layer of clean, coarseaggregate beneath the slab prior to the pour. 5) Install a suctionfan designedfor use in ASD systems. (SuctionFan, Section2.1.1.5) Aggregate Specifications f-2 Sealmajor radonentry routesincluding slaband foun- In most areasof the U.S., subslabaggregate is routinely dation joints and cracks and utility and pipe penetra- installed(and frequently required by code)to provide a drain- tions. (SealingRadon Entry Routes,Section 2.3) agebed for moisture‘and a stable,level surfacefor pouring the slab. The preferred aggregatefor ASD systemsis crushed aggregatemeeting Size #S specificationsas defmed in ASTM C-33-90, “Standard Specificationfor ConcreteAggregates” 12 (11). This aggregateis in the range of l/2 to 1 in. diameter Figure 2-3b iIlustratesthe use of subslabwalls that are with less than 10 percentpassing through a 1/2-m sieveand perpendicularto the corridor but do not crossthe corridor. In hasa free void spaceof approximately50 percent. this example,the subslabwalls would not interrupt the nega- tive pressurefield under the slab unless the subslab wall In September1992, the averagecost for a ton of crushed extendedacross the corridor (not shown in Figure 2-3b). As a stonewas $6.86. This cost representsan averagefor 20 U.S. result, only one radon suctionpit would be needed. cities, with a range from $4.50 to $11.32 per ton (12). For a layer of crushedstone 4 in. deep,this would be about$0.10 to Figure 2-3~ showstwo subslabwalls eachparallel to the $0.25 per ft2. corridor. In this case,the subslabarea is divided into three compartments.For this design,two radon suctionpits would Aggregate Placement probablybe required,or threeif one is installedin the corridor Placea minimum of 4 to 6 in. of aggregateevenly under area. the entire slab, taking carenot to introduceany fine material. Figure 2-3d shows the worst case examplefor a cost- If the aggregateis placed on top of a material with a lot of effectiveASD systemdesign. Subslab walls run both parallel fines and compactionof the aggregateis required for struc- and perpendicularto the corridor, dividing the subslabarea tural or code reasons,a geotextile fabric or an additional into many compartments.For an ASD systemto be effective reinforcedvapor retarder beneath the aggregatecan be usedso with such a design,one radon suctionpit would normally be that fme particles from the natural soil do not mix with the requiredfor each subslabcompartment. aggregate.A vapor retarder should also be placed over the aggregateprior to pouring the slab. Although the vapor re- Figures2-4a and 2-4b illustratethe sideview of theeffect tarder probably will not serveas a stand-aloneradon barrier of subslabwalls on the designof the ASD system.Figure 2-4a (due to inevitableholes and tearsin the plastic), it will keep correspondsto a possibleASD systemdesign for the subslab the wet concretefrom filling in spacesin the aggregatelayer. wall layouts shown in Figures 2-3a and 2-3b. Figure 2-4b correspondsto the ASD systemdesign required for the lay- Drainage Mats outs in Figures2-3~ and 2-3d. For the “worst case” scenario shown in Figure 2-3d, this sideview of the suction points In 13 A Concrete Block Wall Expansion Joint with Backer Rod and , Polyurethane Pourable Sealant Flush with Slab PolyWethane Sealant , -7 Slab-on-Grade .f &.‘_ Aggregate (ASTM Size #5 or Equivalent) 7-- Compacted Soil Figure 2-2a. Interior footing/foundation wall. Not to scale. Concrete Block Wail Slab-on-Grade Aggregate (ASTM Size #5 or Equivalent) Compacted Soil Figure 2-2b. Thickened slab footing. Not to scale. A suctionpit with a minimum exposedaggregate surface systemsin existing buildings becauseof the easeof installa- areaabout 30 tunes the cross sectionalarea of the vent pipe tion. However, new constructionprovides the designerwith entranceis very effective. A concretedrainage distribution the flexibility for selectingthe mostconvenient and effective box or other structurethat meetsthe 30-l ratio shouldalso be location for the radon suction pit and vent stack. When the effective.However, only the constructiondetailed in Figure2- slabis pouredover the radon suctionpit as shown in Figure 2- 5 has beenfield-tested by EPA. As shown in Figure 2-5, the 5, be sure to follow appropriate structural guidelines for vent pipe should enter the radon suction pit horizontally so reinforcedconcrete. that the suctionpit may be locatedin a centrallocation and the verticalvent pipe may be locatedwherever is mostconvenient Location of Radon Suction Pits rather than simply at the pit location. The radon suction pit should be centrally located. A Alternatively,the ventpipe can exit the radon suctionpit centrallylocated pit will provideeven pressure field extension vertically. The vertical approachis normally used for ASD in all directions.Do not locate the pit near subslabbarriers 14 Radon Suction Pit Radon Pipe Riser to be Encased All Interior Walls 7 I Non-Load Bearing 1 Q 2-4a Figure 2.3a. Outside walls and post load bearing. Not to scale. (suchas footings) or nearunsealed openings through the slab. a 4-ft by 4-ft by 8-m. deepradon suctionpit, it is necessaryto As shown in Figure 2-5, the vent pipe shouldenter the radon haveapproximately 240 linear ft of 4-m pipe (with ten 3/4-m. suctionpit horizontally. The vent pipe is then run under the holes per ft). slab,exiting the subslabin a convenientlocation. Onerecently constructed school with 50,000ft2 of ground Number of Radon Suction Pits contactused 11 suctionpoints with 120linear ft of perforated pipe extendingfrom each suction point, totaling over 1300 With the use of a properly designedradon suction pit, linear ft. Field testingby EPA demonstratedthat only one of ASTM Size#5 aggregate,the eliminationof subslabbarriers, the 11 suctionpoints was neededand that the perforatedpipe and sealingof major radonentry routes,one radon suctionpit was not necessaryfor an effectiveASD system(7). per 100,000ft* of slab areashould result in a very effective ASD system.This Figure 2-5 approachwas recently success- Although some designersuse systemswith perforated fully demonstratedby EPA in two largebuildings: one build- pipe insteadof a radon suctionpit (7), this type of systemcan ing is 60,000 ft* in area, and the other is 480,000 ft2. The significantlyincrease construction costs due to both the qtuan- 60,000ft* building is discussedin detail in Appendix A. tity of pipe neededand the cost of placement.Therefore, EPA prefers the radon suction pit approachto installing subslab Subslab Perforated Pipe perforatedpipe. If perforatedpipe is used,size it so as not to significantly reduce the air flow which could normally be Instead of a radon suction pit, some designersprefer achievedthrough the connecting6-m vent pipe. laying perforated polyvinyl chloride (PVC) drainage pipe under the slab and connectingthe perforatedpipe to the vent Interaction With Interior Drainage pipe. Horizontal perforated pipe is not necessaryin ASD systemsif the system is designedas recommendedin this Designersand buildersof housesalso have tried connect- manual.This is becausefor a subslabhorizontal pipe system ing the ASD system into interior footing drainagesystems. to provide the equivalentexposed surface area to aggregateas Although this connectionmight facilitate the functioningof a 15 Figure 2.3b. Interior walls between rooms and outside walls load bearlng. Not to scale. passive System if the System iS airtight, this approachhas not 2.1.1.4 Radon vent Pipe beenevaluated by EPA in schoolsor other large buildings. Specifications Similarly, the use of interior footing drains for water control can affect the pressurefield extensionof an ASD For new constructionof schoolsand other large build- system.Interior footing drainssometimes terminate in a sump ings, EPA recommends6-in. diametersolid PVC pipe. Other hole. If this is the case,the builder must seal the sumphole sizesare available;4-in. pipe is normally used for drainage airtight; if the sump hole is not sealedairtight, building air systemsand plumbing stacksand is easy to route vertically. will be drawn into the sump by the subslabsystem, and the However,if you arenot planningon sealingexpansion joints, pressurefield will be weakened,and pressurefield extension we recommend you use vertical piping at least 6 in. in will be decreased.It is also possibleto use the sealedsump diameter,This sizepipe is necessarysince greater airflow will hole asa radonsuction pit; this approachis commonin houses be neededto produce the samelevel of subslabsuction and (5), but its applicability in schoolsand other large buildings pressurefield extensionas a systemwith sealedexpansion h,asnot beendemonstrated. joints. If interior footing drainsare usedand extendout beneath Building Codes the footing to daylight or to a sewer,the drain mustbe airtight while still allowing water to drain in order for the systemto PVC radon vent pipes are typically used in existing work. Watertraps have been used in houses,but this approach buildingsbecause of their easeof handlingand cost;however, has yet to be demonstratedor evaluatedin schoolsor other building codesin someareas of the country might preventthe use of PVC piping in some sectionsof buildings. For ex- kargebuildings. ample, specialrestrictions sometimes apply to pipe used in firewall penetrationsand plenums above dropped ceilings. 16 Figure 2-3~. Hall and outside walls load bearlng. Not to scale. Also, building codesin someareas require steel pipe; in most drains back to the radon suction pit. Accordingly, it is also Ness, code requires suitable fire stop detailsat any location important to avoid any low areasin the horizontal pipe that wherethe exhaustpiping penetratesa fire ratedwall, a ceiling could block airflow if condensationwere to accumulatein the deck, or a floor deck. Generally,PVC pipe can penetratea pipe. One architecthas noted that, when piping is installedin firewall if a materialto block fire is used.When installing the droppedceilings that may havea drop in temperature,insula- radon vent pipe, make sure you do not violate applicable tion of the piping helps to avoid condensationproblems. codes.For example,the building in the Appendix A case study used Schedule40 PVC pipe beneaththe slab and steel Labeling of System Components pipe abovethe slab in order to meet statecodes. Label the exposedradon ventpipe to identify the pipe as Piping installation a componentof a radon vent systemthat may containhazard- ous levelsof radon.Labels shouldbe placed at regular inter- Attention to detail while installing the verticalrisers will vals (at least every 10 ft) along the entire pipe run. Clearly help ensurethe proper operationand long life of the system. mark all componentsof radon reduction systemsas radon Startingat the floor slab, sealany openingsbetween the pipe reductiondevices to ensurethat future ownersof the building ‘andthe floor slab with a high adhesivesealant (polyurethane do not removeor defeatthe system.At the roof exit, attacha is currentlypreferred). Also, sealall piping joints. An illustra- permanentlabel to the vent with a warning suchas “Soil gas tion of sealingpipe penetrationsthrough the roof is shown in vent stackmay containhigh levelsof radon; do not place air Figure 2-6. Additional details on sealantsand sealing are intake within 25 ft.” Refer to local codes to determinethe providedin Section2.3. specific minimum distancefor air intakes. The suction fan dischargelocation is coveredin greaterdetail in the following It is important that all horizontalpipe runs are pitched a section. minimum of l/8 in. per ft so that accumulatingcondensation 17 r------1 I I I I I I I I I I 1 I I I Radon Suction Pit Radon Suction Pit I 1 1 I i i * . / I I I I I I F-1 I I >; I I I -f I kLw* ~L-e,, Jl -----e-w 1 : 3 .- -__------_--~~------n-x------T Similar Radon Suction Pit I Subslab Footing y!T gzyt!ki ‘S&slab Footing 1 I \ Encased (Typ.) I I I I I L------_-_------___,--____-____------ Figure 2-3d. All interior walls load bearing. Not to scale. / Radon Exhaust Stack Roof Exhaust Fan, Ceiling ii3l 1 Slab-on-Grade Radon Suction Pit Figure 2-4a. Section 1 (corresponds to Figures 2-3a and b). Not to scale. ia Radon Exhaust Stack / Roof Exhaust Fan Radon Exhaust Fan Ceiling Vertical PVC Pipe (Radon) ASTM Size #5 Radon Suctinn Aggregate or Pitt - Equivalent / Figure 2-4b. Sectlon 1 (corresponds to Figures 2-3o and d). Not to scale. 2.1.1.5 Suction Fan being roughed-in,with the fan to be installed later if needed, When to Install installationof the waterproofelectrical connection above the roof during constructionwill facilitateaddition of the fan. A suctionfan can be installed during building construc- tion or the piping can be terminatedand cappedat roof level Suction Fan Discharge and the fan installed later. As discussedpreviously, passive The exhaustdischarge conliguration of an ASD system systems(without a fan) are not recommendedfor radon should be treatedsimilarly to the dischargeof a laboratory control in schoolsand other largebuildings. ASD systemfans fume hood or other rooftop exhaustthat vents toxic fumes. shouldbe operatedcontinuously; otherwise elevated levels of Somebuilding codes,for example,specify that any discharge radon may accumulate.The cost of operatingthe fan contimr- of pollutantsmust be locatedat least 25 ft from any outdoor ously is comparableto the cost of operatingany otherexhaust air intakes.Examples of suitabledischarge configurations are fan in the building (suchas a restroomexhaust fan). presentedin the Industrial Ventilation Manual of Recom- mendedPractices, lgth Edition (13). and the 1989 ASHRAE Fan Selection and installation FundamentalsHandbook (14). Use fans manufacturedspecifically for outdoor use in We recommendthat the ventpipe terminatein a vertical radon control systems.These are availablefrom many ven- position above the roof with sufficient height that the dis- dors in a variety of sizes.Fans normally used for schoolsand charge does not re-enter the buihling. The discharge can other large buildings are in-line duct fans rated from 500 to containextremely high levelsof radon.If this configurationis 600 cfm at zero inchesstatic pressure.Because piping on the not possible,we recommendthat you choosea configuration exhaustside of the fan is underpositive pressure and might be that providesat leasta 1,000to 1 dilution ratio to the nearest subjectto leaks,the fan always shouldbe mountedoutside the air intakeor operablewindow. This dilution ratio is calculated building. Designersshould be aware that leakageinside the from theASHRAE Fundamentals Handbook Chapter 14 equa- envelopeof the building is not acceptable. tions (14). Most installersconnect the fans to the pipe systemwith rubber sewagepipe connectors.This connectionallows for a Warning Device tight seal,quiet operation,and easyreplacement of the fan (if ASD systemdesigners should include a devicethat warns needed).Additional materialsand componentsare normally building owners and occupantsif the systemis not operating included in a systemto satisfy safety needs,system perfor- properly. A preferredwarning systemhas an electronicpres- mance indications, and noise reduction. Typically code re- suresensing device that activates a warning light or an audible quirementsdictate that waterproofelectrical service switches alarm when a systempressure drop occurs.These are readily be placedwithin view of the fan to ensurethat the systemwill availablefrom severalsuppliers. We adviseinstalling a device not be activatedduring maintenance.If the ASD systemis that warns of a pressurechange rather than one that deter- 19 Stack Vented Through Roof Concrete Slab Thickened Concrete Slab 314” Pressure Treated Plywood Clean Coarse Aggregate 8” x 8” x 8” Concrete Block ASTM Size #5 or Equivalent Section A 314” Pressure Treated Plywood Stack Vented Through Roof / - 8” x 8” x 8” Concrete Block t ‘1 r- Figure 2-5. Radon suction pit. Not to scale. mines fan operation. Severalthings can stop a systemfrom openingsin the slabnot only reducesystem effectiveness, but operatingeffectively besides fan operation.Additionally, the also increaseoperating costs by drawing too much air from fan may still appearto be operatingeven though air flow is inside the building. Section2.3 providescomprehensive in- severelyreduced. structionsand guidelinesfor sealing. Install the warning devicein an areafrequently visited by 2.1.2 Operation and Maintenance a responsibleperson, In someschools, warning deviceshave beenplaced near the HVAC controlpanels or in theprincipal’s ASD system operation and maintenanceconcerns fall office. Someschools have chosen to connectthe signalfrom a into threetime frames: warning deviceinto the energymanagement system computer . BeforeOccupancy for the district. . Weekly 2.1.1.6 Sealing Major Radon Entry Routes . Annually For an ASD systemto be mosteffective, it is importantto seallarge openings (such as utility penetrationsand expansion joints) that CNIdefeat extension of a low pressurefield. Large 20 Top of Stack 5’ from Any Air intake Radon Exhaust Fan 4” or 6” PVC Pipe Polyurethane Sealant Applied Behind _ b--kf Turnuo and on Too of theI._ -.-NDm Band Draw Band, Required --.--r ---- -.. --r -. Minimum 1” Tumup Approved Fasteners and Disc - EDPM Boot (Min. of 4) Around Vent Pipe Slip Sheet (if required)- 6” Figure 2-6. Sealing pipe penetratlons through roof. Not to scale. 21 2.1.2.1 Before Occupancy 2.1.2.2 Weekly Measureradon levels in the building at least 24 hours Check the pressuregauge(s) in the radon vent pipes and after the ASD fan is turned on. (Guidelinesfor measuring the system alarm to ensurethat the fan is mainkining ad- radonlevels are briefly coveredin Section2.4 of this manual.) equatenegative pressure to depressurizethe subslabarea. If you have roughed-in an ASD systemwithout a fan, then theseradon measurementswill determineif it is necessaryto 2.1.2.3 Annually activateyour systemwith a fan. Many building ownerscon- Inspect the fan for bearing failure or signs of other tinuously operateASD systemseven if radon levels without abnormaloperation, and repair or replaceif required. the systemare below 4 pCi/L. Continuousoperation of the systemwill further reduce radon exposureto building occu- Inspect the dischargelocation of the vent pipe to ensure p‘ants. that no air intakehas been located nearby, and that a building usagechange has not placedthe exhaustnear operablewin- Measure Subslab Pressures dows. If the building haselevated radon levels, it is importantto Check the HVAC system to determine if it is being confirm that the ASD systemis achievingan adequatenega- maintainedand operatedas designed.Even though the ASD tive pressurefield under all areasof the slab.Measurement of systemmay be functioningas designed,excessively powered the subslabpressure field is commonlyreferred to aspressure exhaust without adequatemakeup air might overcomean field extension(PFE) or subslabcommunication. ASD system. To me Attic/Roof Fan Creates Lower Air Pressure Beneath the Membrane Exhaust Stack Abo~ Roof Pit or Perforated Pipe System Permeable Material or Perforated Pipe Network 8 E Positive Pressure 0 P Negative Pressure Figure 2-7. Submembrane depressurizaiion In crawl space. 23 2.1.5 ASD Cost Estimates . For crawl space substructures, provide for a Estimatedtypical cost rangesfor the materialsneeded for submembranedepressurization system. (Section 2.1.4) an ASD systemare presentedin Table2-l. Material costsand . Install an alarm systemand, to ensureASD system labor costs can vary widely by region. Also, rememberthat effectivenessand longevity, follow all operationand becausemany buildings normally use aggregateand a rein- maintenancerecommendations. (Section 2.1.2) forced vapor retarder under the slab, they are not usually consideredan additional cost of radon prevention. 2.2 Building Pressurization and Dilution The average total cost of conducting diagnosticsand insdbng ~1 ASD system in an existing building is about The heating,ventilating, and air-conditioning (HVAC) $OSO/ft*(9). The total cost of an ASD system for a new system in a modem building has many functions; it must 60,000ft2 building was $5,000(see Case Study, Appendix A). regulatetemperature, humidity, air movement,and air qu‘ality inside the facility. A properly designedand operatedHVAC 2.7.6 Summary of Guidelines for ASD systemcan be usedto reduceradon levels by building pressur- Systems ization and dilution. In Lareaswhere radon is lmown to be a problem, as a New constructionoffers the opportunity to design and minimum, it is advisableto rough-m a soil depressurization install the HVAC systemso that it producesa slightly positive systemthat can easily be madeactive with a fan. Attention to air pressureinside all areasof the building. Pressurizationis dek$l in the design stageof the soil depressurizationsystem accomplishedby bringing more outdoor air into the building will help ensure its success.The following is a review of than is removed.This hasbeen shown to reduceradon levels important guidelines for building and designing an ASD in existing schools.The outdoor air also increasesbuilding system. ventilation,and thus dilutesradon and other indoor conkami- nants. . Place a continuous4- to 6-m layer of the specified aggregateunder the slab. (Aggregate,Section 2.1 .l. 1) The following subsectionscontain designrecommenda- . tions,standards for ventilation,and guidelinesfor installation, Eliminate barriers to subslabairflow such as subslab operation,and maintenanceof HVAC systems.As discussed walls. (SubslabWalls, Section2.1.1.2) in the overview of this document,in radon-prone Table 2-1. Estimated Costs for Primary ASD Components ASD Feature Material Cost Comments Crushed stone (4 in. deep $0.10 to $0.25 per ft* If aggregate is normally used, do not ($4.50 to $11.32 per ton) indude as additional cost. Radon suction pit (4 x 4 ft) Minimal As shown in Figure 2-5. Vent stack (6 in. diameter PVC) $2.00 to $3.00 per ft Total cost depends on pipe run length. Vent stack fittings (6 in. diameter PVC) $20.00 to $30.00 each Total cost depends on system design. 6 mil poly vapor retarder under slab $0.10 to $0.30 per R* Normally included in construction. Suction fan $300 to $500 each As discussed in Section 2.1 .1.5. Firebreaks $100 to $150 each At least one per stack and pit. Sealing joints in concrete $0.40 to $1.50 per linear ft Highly variable, depending on building (typical 40 x 40 ft slab sections) (includes material and labor) design and location. 24 15,000 cfm. However, in Figure 2-8 there is an outdoor air Although building pressurization and dilution can reduce supply of 20,000 cfm, or 20% of the total supply. As a result, radon levels and improve indoor air quality, they do present the building illustrated in Figure 2-8 is under a positive some concerns as a stand-alone radon control technique. pressureand 5,000 cfm of air will exfiltrate from the building. These include: This positive pressure will keep radon from entering the building while the HVAC system is operating. On the other If total building exhaust capacity is not balanced with hand, the scenario in Figure 2-9 shows an outdoor air supply an equal or greater amount of conditioned makeup air of only 5,000 cfm, or 5% of the total supply. In this case,the (outdoor air), the pressurein the building interior will building is depressurizedby 10,000 cfm. This depressuriza- be negative with respect to the subslab area. This tion will cause air to infiltrate into the building and can negative pressure acts as a driving force for radon- exacerbate radon entry into the building. The natural “stack containing soil gas to be drawn into the building. effect” can also contribute to building depressurization. Open windows and doors make it very difficult to To minimize the amount of outdoor air neededto pressur- achieve a consistent positive pressurein the building. ize a building, the shell of the building must, be tightly Start/stop operation of the HVAC system for various constructed.In addition to facilitating building pressurization, occupancy modesdoes not allow for continuous build- a tight building shell will reduce energy costs and allow for ing pressurization.If the HVAC systemis turned off or improved environmental control. For details on measuring air set back during unoccupied periods, then the specific leakagerates, refer to ASTM E779 “Standard Test Method for hours of preoccupancy start-up to reduce radon levels Determining Air Leakage Rate by Fan Pressurization (18):’ that have built up while the system was off should be Note that large buildings may be difficult to test by this determined on a building-by-building basis. method becauseof the larger leakage area. The design and operation limitations of different types Measurements in existing schools show that a slight of HVAC systemsmust be considered when designing positive pressure(as little as +O.OO1 in. WC relative to subslab a system to pressurize the building. For example, the and outdoors) reducesradon levels by preventing radon entry. design of variable air volume (VAV) systems must So, radon entry should be prevented while the HVAC system take into consideration the effects of minimum flow is operating if the building is pressurized. conditions on ventilation and pressurization of the The supply of outdoor air also helps to reduce radon building. levels by dilution. For a given constant rate of entry, radon For additional information on the effects that different concentrations in a building are inversely proportional to types of HVAC systemshave on radon levels in schools,refer ventilation rates. Thus, for example, to reduceradon levels by to the recent EPA report “HVAC Systems in the Current a factor of 10, one would have to increase the air exchange Stock of U.S. K-12 Schools’*(20). rate by that same factor (19). In most cases, such a large exchange rate may be neither practical nor desirable. Exhaust Fan u,wuw~mauaes necycleo Air 80,000 CFM Exhaust 15,000 CFM Positive Pressure From 5 MO CFM E Positive Pressure = Negative Pressure Figure 2-8. Buildlng positive pressurization with HVAC system. 25 Exhaust Fan Infiltration 10,000 CFM -m Infiltration / 10,000 CFM @= Positive Pressure Q= Negative Pressure Figure 2-9. Example of building depressurization with HVAC system. 2.2.2 Standards for Ventilation Seal all supply and return ductwork at all seamsand For many yearsit has been commonpractice to design joints. largebuildings with approximately10% more supplyair than Seal all floor and wall penetrations(especially under return air in order to reducedrafts from infiltration. Following through-wallunits and in mechanicalrooms, see Sec- this sameprocedure in a building with a tight shell is likely to tion 2.3). producea net positivepressure in the building during normal operation. Examplesof recommendedventilation standards Constructthe building “tightly.” for commercialbuildings, from ASHRAE Standard62-1989: Control operationof the HVAC relief dampersso that “Ventilation for AcceptableIndoor Air Quality” (lo), are they modulateto maintaina positive building pressure summarizedin Table 2-2. The ASHRAE guidelinesare being of 0.005 to 0.010 in. WC. Relief dampersshould be adopted by many statesand national building codes as a controlled by sensingthe differential pressureacross standardin new construction.The applicationof this standard, the building shell and modulatingthe relief damperto coupledwith “tight” construction,is expectedto reduceentry maintainpositive pressure in the building. of soil gas and increasedilution of building contaminants. Both the increasedventilation and the pressurizationshould Be sureall applicablebuilding and safetycodes, stan- help to reduceindoor radon levels. dards,and guidelinesare followed. Especiallyimpor- tant in this regard are fue codes,fuel use codes,the 2.2.3 Guidelines for Installation and National Electrical Code, and other safety and me- Operation chanicalcodes. It is not practicalto providespecific radon control guide- Be sure to preservethe intended indoor air quality linesfor designingand operatingevery type of HVAC system. purposesof mechanicalventilation devices.Exhaust However, the following basic guidelinesfor achievingbuild- fans should remove the moisture, fumes, and other ing pressurizationshould be discussedwith the designengi- contaminantsgenerated within the building. Supplyair neersduring the planningstage. systemsshould provide temperedair, free of objec- . Plan the HVAC systemsso that the building interior in tionablequantities of contaminants. all groundcontact rooms is at leastslightly pressurized (for example,0.005 to 0.010 in. WC). Any effect on 2.2.4 Maintenance moisturedynamics and codeacceptability must also be ProperHVAC systemmaintenance is essentialto ensure addressedby the building designers. continuedreduction of radon levels and adequateindoor air quality. This is especiallyimportant in areasknown to have . Avoid subslabsupply and/or return ductwork. radon problems.The following items are intendedfor build- . In radon-proneareas, do not locateair supplyor return ing owners and operatorsto assist in proper operation and ductwork in a crawl space(10). maintenanceof HVAC systems. 26 Table 2-2. Examples of Outdoor Air Requirements for Ventilation in Commercial Facilities (Source: ASHRAE Standard 62-1989) Type of Facility Estimated Occupancy, Outdoor Air Requirements Persons per 1000 ft2 of floor Area (&n/Person) Non-smoking Area Lobbies 30 15 Conference Rooms 50 20 Assembly Rooms 120 15 Dormitory Sleeping Areas 20 15 Office Spaces 7 20 Reception Areas 60 15 Smoking Lounges 70 60 Barber Shops 25 15 Beauty Shops 25 25 Supermarkets 8 15 Ballrooms & Discos 100 25 Transportation Waiting Rooms 100 15 School Classrooms 50 15 School Laboratories 30 20 School Auditoriums 150 15 Hospital Patient Rooms 10 25 Operating Rooms 20 30 Correctional Cells 20 20 Note: For complete listing refer to ASHRAE Standard 62-1989 (10). Annually ating under minimum outdoor air conditions. This positive pressurizationwill reduce radon entry, and the additional . Replaceair filters at least twice a year if high quality, outdoor air will help to dilute radon that does enter the medium efficiency pleated air filters are used and building. more frequentlyif non-pleatedor disposablelow effi- ciency filters are used. A building designedto control indoor air contamimants (including radon) shouldinclude: . Check the HVAC systemand exhaustfans to deter- mine if they are being operatedas designed.Excessive . Pressurizedground contact rooms exhaustwithout adequatemakeup air will depresstuize . the building, rendering building pressurizationinef- A well-balancedair distribution system fective. . Adequatemakeup air . Inspect the HVAC systemcomponents and controls . A tight building shell (lessthan 1.0 ach at 25 Pa) for failure or signsof faulty operation(such as lossof dampercontrol) that would restrict the supply of out- Mechanicalsystems should be designedand installedto door air. Note: two states,California and Maine, cur- meet the needs of occupanthealth, safety, comfort, energy rently requireannual inspections for correctoperation conservation,and building longevity. Meeting these needs of the ventilation systemsin schools;other statesare requiresan understandingof how the climate, the building, consideringsimilar requirements. and the occupantsinteract. Building pressurizationalone, however,cannot always consistentlyprevent radon entry.For . If an ASD systemis also installed, inspect the dis- example, operable windows can make it very difficult to chargelocation of the ASD ventpipe to ensurethat an achieve pressurization.A properly designed and operated air intake has not been located nearby, or building mechanicalsystem, in conjunctionwith an ASD systemand usagechange has not placedthe exhaustnear operable sealing of major radon entry routes, should provide cost- windows. effectiveradon preventionin new buildings. Once Every 5 Years 2.3 Sealing Radon Entry Routes . Test and balance the HVAC system.Rebalance the This section on sealing radon entry routes covers the systemas renovations and usagechanges occur. following topics: 2.2.5 Summary of Building . RecommendedSealants (2.3.1) Pressurization Guidelines . SealingConcrete Slabs (2.3.2) In a building with a tight shell, slight positivepressuriza- . SealingBelow-grade Walls (2.3.3) tion can be achievedby supplying about 10% more outdoor air than is mechanicallyexhausted when the building is oper- . SealingCrawl Spaces(2.3.4) 27 Recommendedsealants for radon-resistantnew construc- is alwaysa potentialradon entrypoint. To facilitate sealingof tion arebriefly coveredin Section2.3.1. Sections 2.3.2.2.3.3, this joint after construction, contractors have deliberately and 2.3.4 cover sealingthe most commonradon entry routes. createda significant floor/wall joint detail so that it will be Section2.3.2 is applicableto ah three substructuretypes - easy to work with and seal. One approach is to install an slab-on-grade,basement, and crawl space- that are con- expansionjoint with the top l/2 to 3/4 in. of the joint remov- structed with poured concrete slabs. Section 2.3.3 is appli- able after the concrete sets. This approach leaves enough cableto basementsubstructures. Section 2.3.4 providesaddi- spacefor sealingwith a suitablepolyurethane caulking before tional sealingrecommendations for limiting radonentry from floor covering is installed.Another approachis to round the the crawl spaceinto the building interior. slab at the floor/wall joint with an edgingtool and sealit with polyurethanejoint compound.The expansionjoint shouldbe On-goingEPA researchon radon-resistantnew construc- as thin as possible (or eliminatedif code permits) to make tion in homeshas encountered numerous difftculties in achiev- sealingeasier. It is importantto sealthis joint during construc- ing a reliable, gastightphysical barrier between the soil gas tion becausethe joint is ofteninaccessible after the building’s andthe building (5). This researchindicates that a nearperfect walls are raisedand floor coveringis laid. sealingjob is necessaryto achievehigh radon reduction in homesusing sealing as a stand-aloneradon reduction tech- Architectsand engineersshould also be awarethat build- nique in radon-prone areas. Becauseof the difftculties of ings constructedwith a combinationof different substructures achieving complete sealing, it is normally much more cost may haveadditional entry routesat the interfacebetween the effective to include ASD (Section2.1) and adequateHVAC two types of substructures. systemdesign and operation (Section 2.2) in the designof new buildings in radon-prone areas. However, sealing of Pour Joints and Control Saw Joints major radon entry routes (as discussedbelow) and good Cracksare difficult to avoidwhen largeconcrete slabs are constructionpractice will enhancethe performanceof both poured.To minimize cracking,builders either usepour joints ASD ‘andHVAC radon preventiontechniques. becausethe slab was poured in sections,or saw-cutthe slab (control saw joints) to control where a crack will occur, or 2.3.1 Recommended Sealants both. If neither of these techniquesnor post-tensioninghas Se‘alantsused for radon-resistantapplications must have beenemployed, larger slabswill crackunevenly in unpredict- good adhesionto concreteand be durable and elastic. The able locations. To facilitate sealing these cracks,make the popularity of polyurethaneas a suitable elastomericjoint joint or saw-cutlarge enoughto sealwith polyurethanecaulk compoundis basedon a combinationof strong adhesionto after the slab sets.To sealproperly, both sidesof cold joints concreteunder difficult conditions,long servicelife, andgood shouldbe tooled when poured and then sealedwhen cured. elasticity (5). Avoid silicone caulks becausethey do not adhereto concretewell. 2.3.2.2 Slab Penetrations and Openings Whenyou apply sealants,be suresurfaces are clean,dry, Major slab penetrationsand openingsshould be seaIedto and free of grit and that the surface temperatureis above reduceradon entry and to improveASD and building pressur- freezing.Apply sealantsin accordancewith themanufacturer’s izationsystem performance. These slab penetrations and open- recommendedpractice. Typical dimensionsfor caulk beads ings include utility penetrationsand sumpholes. are l/2 in. deepby l/4 in. to l/2 in. wide. It may be necessary Utility Penetrations to use backerrod when applying sealantin wide gaps. Examplesof utility penetrationsthrough the slabinclude 2.3.2 Sealing Concrete Slabs water and sewer lines, utility lines to unit ventilators ‘and This sectioncovers all buildings constructedwith con- radiators,electrical serviceentries, subslab conduits, air con- creteslabs: slab-on-grade, basement, and crawl space. ditioner condensatedrains, and roof drains. The openings aroundthese slab penetrationsshould be sealedwith polyure- Concreteis normally a good radon barrier. The major thane caulks. Many builders use plastic sleevesto protect problemswith concreteslabs are joints, slabpenetrations, and metal pipes from corrosionwhen they passthrough the con- cracks.The following subsectionsprovide guidance on avoid- creteslab. These sleeves can be removedafter the concreteis ing theseproblems by: 1) sealingslab joints, penetrations,and set, and the spacearound the pipe can then be sealedwith openings:2) preventingrandom cracks in slabs;and 3) using polyurethanecaulk. The sametechniques should be used for subslabmembranes. For additionalinformation, refer to Con- pipespassing through block walls. crete Floors on Ground (21) and Guide for Concrete Floor and Slab Construction (22). In mostconstruction, floor drainsempty into a sewerpipe rather than the soil. In thesecases, the drain itself is not of 2.3.2.1 Slab Joints concern as a radon entry route. The only concern is the Slabjoints of concernfor radon entry include the floor/ openingaround the pipe penetrationas discussed above. Where w 28 Sump Holes Use higher strength concrete: Typical school concrete slab constructionuses concrete with a 28&y compressive Although sump holes are rare in new constructionof strengthof 3,000to 3,500psi. Concretecan be madestronger largebuildings, they are occasionally used as collection points by increasing the cement content, by reducing the water/ for a subslabdrainage system. The sump hole can createa cementratio, or both. radon collection systemthat shouldnot be open to the build- ing interior. An alternativesubslab drainage system is onethat 2.3.2.4 Subslab Membranes drains by gravity to daylight, serving the samepurpose as a Membranesof plasticsused to control liquid water pen- sump hole without the radon entry routes. If draining to etration and water vapor diffusion also are effectivein con- daylight is not possible,then seal the sumphole so that there trolling air movement.If they can be adequatelysealed at the are no air leaks to the building interior. Seal the sump hole joints andpenetrations and installedintact, membranes CNI be with a gasketand lid, and ventthe sumpto the outdoorsusing used in conjunction with the sealedconcrete slab to help plastic pipe (as discussedin Section 2.1.1.3). Also install a providea physicalbarrier to radonentry. The useof a polyeth- submersiblesump pump to removeany water collectedin the ylene vaporretarder will also enhancethe effectivenessof an sump through a check valve to approved disposal. Sealed ASD systemby keeping wet concreteout of the aggregate surnpshave been used as suction pits for ASD systemsin during pouring. housesby attachinga fan to the PVC pipe (15); however,this approach has not been field-tested in schools and is not Many typesof membranesare availableincluding: poly- recommended. ethylene film, reinforced polyethylene film, polyethylene- coatedkraft paper,PVC membranes,and EPDM membranes. Radonmitigators sometimes use silicone rather thanpoly- Polyethylenesheeting is commonlyused as a subslabvapor urethanecaulks for sealingsump lids and accessports because retarderin most areasof the country.The currentprevalence theymake a tight fitting gasketthat canbe removedat a future and low cost of this material indicate it is worthwhile to date.This is satisfactoryif the sumpcover is bolteddown and continue its use even though it is an imperfect barrier for the sealis airtight. radon. 2.3.2.3 Crack Prevention 2.3.3 Sealing Belo w-Grade Walls Cracking of concrete is a natural result of the curing Below-grade walls and stem walls are normally con- process.Factors that affect the curing processinclude water structedof eitherpoured concrete or masonryblocks. Because content, cementcontent, aggregatecontent, humidity, tem- thesewalls are in direct contact with the soil, they can be perature,carbon dioxide levels,air movementover the slab major radon entry routes.This sectiondiscusses the different surface,and preparation of the subslabarea. Reinforcement is typesof below-gradewalls and the coatingsthat cranbe used one of the methodstypically used in large slabs to reduce to sealthese walls. Penetrationsand openingsthrough below- cracking.Concrete should be reinforcedand placedin accor- gradewalls into the soil can also be majorradon entry routes. dance with American Concrete Institute (ACI) codes and Thesepenetrations and openingsshould always be sealedas standard practice. AC1 publishes a number of documents discussedin Section2.3.2.2. outlining standardpractice. A numberof theseapply to crack prevention.Specifically, the readeris referredto AC1302.1R- 2.3.3.1 Wall Types 89, Guide for ConcreteFloor and Slab Construction(22). Poured Concrete Walls The builder should @eatthe slab in one or more of the In schoolsand other large buildings, foundation walls following ways to reduceslab cracking. madeof pouredconcrete are generallyconstructed to a mini- Reinforce with ferrous metals: Imbeda combinationof mum compressive strengthof 3,500 psi. A poured concrete rebarand wovenwire meshin the slabto increaseits strength. wall can be an excellent barrier to radon; however, as with concreteslabs, the major problems are cracks,joints, and Reinforce with fibers: Various fiber additivesare avail- penetrations.We recommendthat concretewalls be built in able to reinforcepoured concreteand reducecracking. These compliancewith guidelinesestablished by AC1 to ensurea fibers are discussedin AC1 544, State-of-the-ArtReport on strongfoundation and to minimize cracking(24,25). Fiber-ReinforcedConcrete. Masonry Block Walls Use water-reducing admixtures: Theseadmixtures (also known as plasticizers)retain workability at a lower water Foundationwalls built of concretemasonry units can be content,increasing the strengthof the concreteslab. SeeAC1 designedwith open cores,filled cores,or cores closedat or 212.1R-89, Admixtures for Concrete,for more information nearthe top courseor at slablevel. In addition,masonry walls (23). are frequentlycoated with an exterior cementitiousmaterial (referredto as “parging”) for water control. This coating is Cure properly: Proper curing is critical to the strength usually coveredat the bottom of the wall to make a good ‘2nddurability of poured concrete.Stronger concrete can be exterior seal at the joint betweenthe footing and the block achieved by slowing the drying rate. Approachesinclude wall. Other types of coatingsare discussedbelow in Section watering the slab during drying, covering it with wet sand, 2.3.3.2.Uncoated blocks are not effective water or Soil-gas wet sawdust,or a waterprooffilm, or coating it with a curing barriers. compound. 29 Concreteblocks are more porous than poured concrete, . Coal tar modified polyurethane: coal tar modified although the parge or waterproofmgcoats can moderatethe polyurethaneis a cold-applied liquid waterproofmg difference.Recent EPA laboratory testshave confiied that system.The coatingdries hard but has someelasticity. concrete masonry walls can allow substantialairflow, al- One problem with this material is that it can be at- though there is a great deal of variation in the porosity of tackedby acidsin groundwater,but it can be defended blocks (26). by a protectionboard. The performanceof any liquid- applied waterproofingsystem is limited by the capa- Whenmasonry construction is used,it is mandatorythat bilities of the applicator,and it is difficult to achieve concreteblock walls be built according to guidelinesissued evencoats on vertical surfaces(5). by the National ConcreteMasonry Association(NCMA) and AmericanConcrete Institute/American Society of Civil Engi- . Polymer-modifiedasphalt: polymer-modified asphalt neers.Their publications cover thiclmessof block, reinforc- is anothercold-applied liquid waterproofmgsystem. ing, pilaster location, control joints, sequencingand other As with the systemmentioned above, the quality of the issuesthat influencecracking and foundationstrength (5). installationdepends on the applicator,and it is difficult to achievean evencoating on a vertical surface.High Stemwalls and Interior Walls gradepolymer-modified asphalt is superiorto coal tar Stemwalls,also called frost walls, are below-gradefoun- modified polyurethane in elasticity, crack-spanning dations that support the load of the above-gradewalls, and ability, and resealability, but inferior in its resistance thereby,the roof. There is a footing beneathstemwalls below to chemicals(5). the frost line. The sealingof the slab/stemwalljoint is covered . Membranewaterproofing systems:membrane water- under Section2.3.2.1. proofing is advantageousover liquid-appliedsystems If stemwallsare constructedof concreteblocks, then the in that quality control over thicknessis ensuredby the top blocks must be solid. This solid block can help prevent manufacturingprocess. Most membranesystems 30 2.3.4 Sealing Crawl Spaces Openingsaround utility penetrationsthat passthrough Elevatedlevels of radon can also build up inside a crawl the slab shouldbe thoroughly sealed. space,especially if the crawl spacehas an earthenfloor rather Drain footing and interior drainagesystems to daylight thana pouredconcrete slab. Radon in the crawl spacecan then if possible.If a sumphole is necessary,a submersible enterthe occupiedarea above the crawl spacethrough cracks pump should be used, the hole sealedairtight to the and openingsin the floor. Thorough sealingof thesecracks building, and the sumpvented to the outdoors. ‘andopenings will help to reduceradon entry into the occupied 31 If major renovationsto a building or HVAC system are planned,retest the building beforehand.If elevated radon levels are detected,incorporate radon-resistant featuresas part of the renovation. 32 Appendix A Case Study Application of Radon Prevention Design Features to a Johnson City Rehabilitation Hospital Building Background Information retarder was placed on top of the aggregateprior to In late 1990 and 1991, EPA had the opportunity to pouring the slab. demonstrateASD in a large hospitalbuilding underconsuuc- 3. Sealingof all pour and control sawjoints and any slab tion in JohnsonCity, Tennessee(6.7). The hospitalbuilding penetrationswith a polyurethanecaulking. (No expan- is one story with a floor area of about 60,000 sq ft. The sion joints were usedin the building.) building is slab-on-gradeconstruction with no foundation walls penetratingthe slab. Mechanicalpiping, electricalcon- 4. Installationof one subslabradon suctionpit, as shown duit, and structuralcolumns penetratethe slab with the col- in Figure 2-5. The pit was locatedin the approximate umns sitting on footings beneath the slab. These columns center of the slab and had a 6-in. stack leading to the supportsteel beams overhead which in turn carry thebar joists roof. If a radonproblem were found when the building for the roof (post-and-beamconstruction). was completed,plans were to install a turbo fan ca- pable of moving 500 cfm of soil gas at zero static This type of constructionis usedin mostcommercial and pressure. industrial buildings currently being built in the U.S. where dimensionsare large in both directions(length and width). All 5. Continuousoperation of the HVAC fans in order to internal walls are gypsum board on metal studs, and the pressurizethe building in all areasexcept those where exteriorwalls are metal stud supportinggypsum board on the negativepressure is necessaryto control odors, nox- inside surfaceand an exterior insulation finish systemon the ious chemicals,or infectiousdiseases (toilets, kitchen, outside. pharmacy,soiled linens ares,isolation wards,etc.). The 4-m thick slab waspoured over a 6 mil vaporbarrier Results underlainwith a 4-in. layer of coarse,crushed aggregate that AI1 of the above recommendationswere acceptedand was continuousunder the entire slab. The slab was divided incorporatedinto thebuilding design.Upon completionof the into about 15 ft squaresby a combinationof pourjoints (1,000 shell of the building and sealing of the slab, EPA made linear ft) andcontrol sawjoints (5,000linear ft). No expansion diagnostic measurementsto determineeffectiveness of the joints were used.Turned down exterior foundationwalls were ASD systemin depressurizingthe entire subslabarea. (Refer used, eliminating an exterior floor-to-wall joint. In other to “MeasureSubslab Pressures” in Section2.1.2.1.) Test holes words, the slab, exterior foundationwalls, and footings were were drilled through the slab at varying distancesfrom the poured monolithically. radon suctionpit, including a seriesaround the entire pcrim- EPA wasrequested to review the plansand specifications eter about6 ft from the slabedge. Radon levels below theslab and to recommenda radon mitigation systemsince the region were measuredby *‘sniffing” with a continuousmonitor and was known to have high radon potential. After this review, rangedfrom about200 to 1,800pCi/L,. five recommendationswere made to the architectdesigning A suction fan was attachedto the radon vent stack in the building and incorporatedin the plans and specifications. order to determinethe subslabpressure field. The suctionfan 1. Good compactionof the clay soil under the aggregate movedabout 200 cfm of soil gasat a vacuumof about 1.5in. to decreasepermeability of the material under the WC. Subslab pressuremeasurements wcrc made using a aggregate. micromanometer.Negative pressure was 0.47 in. WC in the radonsuction pit, 0.22 in. WC 50 ft from theradon suctionpit, 2. Minimum of 4 in. of crushedaggregate-meeting Size and 0.18 in. WC at the farthest point on the perimeter (a #.5specifications as definedin ASTM C-33-90(ll)- distanceof 185 ft). This is consideredextremely good cxtcn- carefully placed so as not to include any soil. The sion of the negativepressure field. Extrapolationof thesedata stonewas not tampedafter it was placed,and a vapor indicatesthat the mitigation systemcould mitigate a slab as large as 1,OOO,OOO fL2. 33 Upon completionof the building, radon levelswere mea- Table A-l. Cost of Mitigation System In Johnson City suredin half of the building using open-facedcharcoal canis- Hospital ters. The I-IVAC and the ASD systemswere off for this first Change Order Description set of measurements.Radon levelsranged from lessthan 0.5 cost ($) pCi/L (lowest detectablelevel with the open-facedcanisters Change aggregate to ASTM Size #5 stone 0 used)to 53 pCi/L. The highestlevels were in the bathrooms, Seal all slab cracks and penetrations 2583 particularly thoseattached to the patient rooms. The patient with polyurethane caulking room with the highest bathroom radon level had a radon Install subslab suction pit and stack to roof 1275 readingof 10pCi/L. This was the highestradon level found in Install suction fan and alarm system 1510 any non-bathroomarea in the buihling. Total cost $5368 To determinethe effect of the HVAC systemalone, the entire building was then measuredwith the HVAC systemon and the ASD systemoff. Again, someof the bathroomshad elevatedradon levels as did someof the patient rooms. The A low cost, single point ASD system,installed during bathroomwith the highestradon reading was again the high- construction,has lowered radon levels in a one-story60,000 est in the building with the I-WAC operating,testing 6 pCi/L. ftz hospitalbuilding to nearambient levels. LeveIs as high as 53 pCi/L were measuredin the building with both the HVAC The final seriesof testswere madewith both the HVAC and ASD systemsoff, and levels as high as 16 pCi/L were und ASD systemsoperating. The 20 bathrooms with the measuredwith the HVAC system operating and the ASD highestradon levelsin the secondseries of testsand manyof systemoff. the patient rooms were remeasured.No measurableradon levels were found in any of the rooms tested.This is not The featuresof this radon-preventionsystem are: surprising in view of the relatively high negativepressure 1. Slab-on-gradepost-and-beam construction with no bar- under the entire slab with the ASD systemin operation. riers to soil gas flow below the slab. In the Indoor Radon AbatementAct of 1988, the U.S. 2. Continuouslayer of coarse,narrow particle size range Congressset a long-term goal of reducing the radon level in crushedaggregate a minimum of 4 in. thick. all buildings in the U.S. to a level as low as that surrounding the buildings (i.e., ambient).This building, built in a radon- 3. Careful sealingof all slabcracks and penetrationsand prone area,appears to meetthe long-termambient goal. the useof a 6-mil plasticfilm betweenthe slab and the aggregate. Conclusions 4. Low permeabilitylayer beneaththe aggregate.(In this Incrementalcosts of theseradon prevention features were case,the compactedclay beneaththe aggregateditself easily tabulatedsince the contractfor thebuilding hadbeen let was highly impermeable.) before the ASD systemwas added to the design.Hence, the cost of the ASD system and sealing was covered by four 5. A subslabradon suctionpit having a void to aggregate changeorders for which the constructioncontractor charged interfacearea of 5 to 7 ft2and a 6-in. diameterstack to an additional $5,300.This is less than $0.10per sq ft of floor the roof. space.Specifications had alreadycalled for 4 in. of aggregate under the slab, and there was no charge for the changein 6. An exhaustfan (on the stack)capable of exhaustinga aggregatesize used. The other three changeorders covered minimum of 500 cfm at no head. installation of the radon suction pit and stack to the roof, For additionaldetails on this and other casestudies, refer sealingof all pour and control saw joints with a poIyurethane to References3,4,6,7,8, and 16. caulking,and installationof the suctionfan and alarmsystem. The costs of the four changeorders are summarizedin Table A-l. A survey of eight recently constructedschool buildings showed that the cost of installing radon mitigation systemsduring constructionranged from $0.30 to over $1.00 per sq ft (8). Hence, the mitigation systeminstalled during constructionin this new building cost only a fraction of the cost of systemsinstalled in the eight schools. 34 Appendix B References 1. U.S. EnvironmentalProtection Agency, U.S. Depart- ing, Refrigerating and Air-Conditioning Engineers, ment of Health and Human Services,and U.S. Public Inc., Atlanta, 1989. Health Service.A Citizen’s Guide to Radon (Second Edition), May 1992. 11. American Society of Testing and Materials (ASTM C-33-90), Standard Specification for Concrete Ag- 2. U.S. EnvironmentalProtection Agency. Radon Re- gregates,1990. duction Techniques in Schools-Interim Technical Guidance.U.S. EPA Offtce of Radiation Programs. 12. EngineeringNews Record,September 7.1992, pg 45. EPA-520/l-89-020 (NTIS PB90-160086). October 13. Industrial Ventilation 19* Edition: A Manual of Rec- 1989. ommendedPractices, Committee on Industrial Venti- 3. Leovic, K.W. Summaryof EPA’s Radon Reduction lation, Lansing, MI, 1986. Researchin SchoolsDuring 1989-90.U.S. EPA, Of- 14. 1989ASHRAE FundamentalsHandbook, Chapter 14, fice of Researchand Development.EPA-600/8-90- page 14.4,Figure 17. 072 (NTIS PB91-102038).October 1990. 15. U.S. Environmental Protection Agency. Radon Re- 4. Craig, A.B., K.W. Leovic, and D.B. Harris. Designof duction Techniquesfor DetachedHouses-Technical radon resistantand easy-to-mitigatenew schoolbuild- Guidance(Second Edition). EPA-625/5-87-017,Janu- ings. Presentedat the 1991 InternationalSymposium ary 1988. on Radonand RadonReduction Technology, Philadel- phia, PA, April 1991. 16. Pyle, B.E. and K.W. Leovic. A Comparisonof Radon Mitigation Optionsfor Crawl SpaceSchool Buildings. 5. U.S. EnvironmentalProtection Agency. Radon-resis- Presentedat the 1991 Symposiumon Radon and Ra- tantConstruction Techniques for New ResidentialCon- don Reduction Technology,Philadelphia, PA, April struction-Technical Guidance. Office of Research 1991. and Development.EPA/625/2-91/032. February 1991. 17. Dutt, G.S., D.I. Jacobson,R.G. Gibson, and D.T. 6. Craig, A.B., K.W. Leovic, and D.B. Harris. Designof Harrje. Measurementof Moisturein Crawl SpaceRet- New Schoolsand Other Large Buildings Which are rofits for EnergyConservation. Presented at the Build- Radon-Resistantand Easyto Mitigate. Presentedat the ing ThermalEnvelop Coordinating Council, Ft. Worth, Fifth InternationalSymposium on the Natural Radia- TX, 1986. tion Environment,Salzburg, September 1991. 18. American Society of Testing and Materials (ASTM Craig, A.B., D.B. Harris, and K.W. Leovic. Radon E779), Standard Test Method for Determining Air Preventionin Constructionof Schoolsand Other Large LeakageRate by Fan Pressurization,1987. Buildings-Status of EPA’s Program.Presented at the 1992 International Symposiumon Radon and Radon 19. Cavallo, A., K. Gadsby, and T.A. Reddy. Natural ReductionTechnology, Minneapolis, MN, September BasementVentilation as a Radon Mitigation Tech- 22-25, 1992. nique.EPA&O/R-92-059 (NTIS PB92-166958).April 1992. Craig, A.B., K.W. Leovic, and D.W. Saum.Cost and Effectivenessof Radon Resistant Features in New 20. Parker,J.D. HVAC Systemsin the Current Stock of SchoolBuildings, Healthy Buildings-IAQ’9 1,Wash- U.S. K-12 Schools.EPA-600/R-92-125 (NTIS PB92- ington, D. C., September4-8,199l. 218338).July 1992. Leovic, K.W., H.E. Rector, and N.L. Nagda.Costs of 21. Portland Cement Association, Concrete Floors on Radon Diagnosticsand Mitigation in School Build- Ground,Skokie, IL, 1990. ings. Presentedat the 85th Annual Meeting and Exhi- bition of the Air and WasteManagement Association, 22. AmericanConcrete Institute (AC1 302.1R-89),Guide KansasCity, MO, June 21-26, 1992. for ConcreteFloor and SlabConstruction, Detroit, MI, 1989. 10. ASHRAE 1989.Ventilation for AcceptableIndoor Air Quality. Standard62-1989. American Society of Heat- 23. American Concrete Institute (AC1 212-lR-89), Ad- mixturesfor Concrete,Detroit, MI, 1989. 35 24. American Concrete Institute (AC1 318-89). Building 26. Ruppersberger,J.S. The Use of Coatings and Block Code Requirementsfor ReinforcedConcrete, Detroit, Specificationto ReduceRadon Inflow ThroughBlock MI, 1989. BasementWalls. In: Proceedings:The 1990 Intema- tional Symposiumon Radon and Radon Reduction 25. AmericanConcrete Institute (AC1 31&l-89), Building Technology.Volume 2: SymposiumOral Papers(Ses- Code Requirementsfor StructuralPlain Concrete,De- sions V-IX). EPA-600/g-91-026b (NTIS PB91- trait, MI, 1989. 234450),July 1991. 36 Appendix C EPA Regional Offices and Contacts Region 1 - Region 6 (CT, I-9 MA, IQ%RI, V (AR LA NM OK. TX) JFK FederalBuilding 1445Ross Ave. Boston, MA 02203 Dallas TX, 75202 Attention: RadiationProgram Manager Attention: Radiation ProgramManager (617) 5654502 (214) 655-7223 Region 2 Region 7 (NJ, NY) (IA, KS, MO, NE) 26 FederalPlaza 726 MinnesotaAve. New York, NY 10278 KansasCity, KS 66101 Attention: RadiationProgram Manager Attention:Radiation ProgramManager (212) 2644418 (913) 551-7020 Region 3 Region 8 (DE, DC, MD, PA, VA, WV) (CO, MT, ND, SD, UT, WY) 841 ChestnutBuilding 999 18thSt. Philadelphia,PA 19107 DenverPlace, Suite 500 Attention: RadiationProgram Manager Denver,CO 80202-2405 (215) 597-8320 Attention: RadiationProgram Manager (303) 293-1709 Region 4 Region 9 (AL, FL, GA, KY, MS, NC, SC, TN) 345 CourtlandSt. N.E. (AZ, CA, I-K W Atlanta, GA 30365 75 HawthorneSt. Attention: RadiationProgmm Manager SanFrancisco, CA 94105 (404) 347-3907 Attention:Radiation ProgramManager (415) 744-1045 Region 5 Region 10 (IL N ML MN OH, WI> 77 West JacksonBlvd. (AK, ID, OR, WA) Chicago, IL 60604 1200Sixth Ave. Attention: RadiationProgram Manager Seattle,WA 98 101 From: IN, MI, MN, OH & WI: Attention: RadiationProgram Manager (800) 621-8431 (206) 442-7660 From: IL: (800) 572-2515 37 Addendum This addendum to the technical guidance manual, “Ra- CMUs turned on their sides.In the school where this was first don Prevention in the Design and Construction of Schoolsand demonstrated,the contractor made the change to all interior Other Large Buildings,” is included in this printing of the walls at no extra cost. Basedon these resuits, we recommend manual in order to make available new technology which has that blocks be turned on all interior walls in buildings in which been developed and field-verified since the manual was ini- ASD is installed except toilet walls serving as pipe chases. tially printed. In the future, the entire manual will be revised These should not be turned and should be sealed from any and all new technology, including this addendum, will be open contact with the subslabaggregate. incorporated into the body of the manual. Increasing Pressure Field Extension by Improved Suction Pits Modifying Subslab Walls The suction pit recommendedin the manual is described in Section 2.1.1.3 (page 13) and illustrated in Figure 2-5 (page Section 2.1.1.2 describesthe effect of subslabbarriers on 20). Since the manual was issued, two new suction pits of pressurefield extension (PFE). It states,“...the designershould improved design have been developed and field-tested. The consider ‘connecting’ subslab areas by eliminating subslab first is shown in Figure 2-12. It is constructed from angle iron walls...under interior doors....Subslabcommunication could which supports a covering of expanded metal decking. This also be facilitated by using subslab ‘pipe sleeves’ to connect new suction pit is smaller (3 by 3 ft in areaand 12 in. deep) but areasseparated by subslab walls.” has the same void-to-aggregate interface (7 ft*) as the one shown in Figure 2-5. Another technique, now field-tested, has been shown to be extremely effective in improving PFE through block walls. The second new suction pit is smaller and much simpler Every other concrete masonry unit (CMU) is turned on its side to construct. It is shown in Figure 2- 13. It is constructedfrom in the first row of block below the slab in interior walls. This a rolled cylinder of expandedmetal decking with a sheetmetal allows soil gas to passthrough the subslabwall, significantly top and bottom. When it is 8 in. tall and fitted with a 6 in. improving PFE. PFE tests have shown that this essentially stack, it will exhaust an area of at least 20,000 ft*. When the makes the wall disappear as far as PFE is concerned. This area to be covered is less than about 10,000 ft*, the pit can be technique is shown in Figures 2-10 and 2- 11. In one field test, 6 in. tall and fitted with a 4 in. stack and a smaller fan if the adequate negative pressure was still maintained after the distance between the pit and the fan is not too great (less than pressurefield had passedthrough four successivewalls with about 20 ft). 38 Figure 2-10. Every other lnterlor wall block Is turned on Its side to allow soll gas to pass through. CMU Wall 4” Concrete Slab on 10 mil Vapor Barrier Seal All Slab Joints & Pipes Lintel Block Filled with Concrete . , u/Y./I ,v I \U h I Ik/, - - - Turn Every Other 6”x6”~16” CMU Horit. So Soil Gas Can Pass Through - Footing Figure 2-11. Interior CMU wall. 39 11/2”x18 Ga.TypeB Gab. Mtl. Deck 6 - #4 Rebar x 8’ 0” Long I E.W. Centered Over Pit 6” Suction Pipe Angle 2x2x1/4” cont. Poured Concrete Angle 2x2x1/4” Vert. Base T 8 B Around @ ea. Comer \ Perimeter of Pit Expanded Metal on All 4 Sides Welded to Angle Supports Figure 2-12. Revised subslab suction pit Rigid 6” or 8”x48” #13 Expanded Metal Decking (1/2”xl”) Direction Rolled into Cyhnder and Overlap Welded Steel Plate wee;;0 Metal Decking 4 112” Hole for 4” Suction Pipe (6” Pit) Cylinder 6 l/2” Hole for 6” &tion Pipe (8” Pit) Figure 2-13. Smaller subslab suction pit. 40 fi U.S. GOVERNMENT PRINTING OFFICE: 1994 - 5 5 0 - 0 0 1 / 0 0 1 6 0 9 lO/Z6-t1&19iVd3 OOE$ esn epy~d 10) Kyeuad ssaupg piygjc~ SE-0 ‘ON lIWkl3d Vd3 alvd S333 ‘8 39VlSOd mm ma