A Quick Reference on Closed Crawl Spaces www.crawlspaces.org

Getting Started Both scientific research projects and real-world installations demonstrate that properly closed crawl DESIGNING CLOSED CRAWL SPACES spaces can provide much better moisture control than The recommended components of a good design fall into six major categories: conventional, -vented crawl spaces in temperate- humid climates. with closed crawl spaces Moisture Management Pest Control ■ ■ (often also called “sealed,” “unvented” or ■ A runoff system to direct water away A termite inspection gap at the top of the Insulation at the sub- or at the perimeter “conditioned” crawl spaces) also can save from the perimeter wall to facilitate detection wall to provide the R-value required by the ■ local residential code. Note that perimeter significantly on energy when compared to homes with ■ Batt insulation in the band area of wall- Site grading and landscaping that directs insulation may be located on the interior wall-vented crawl spaces. ground surface water away from the house insulated closed crawl spaces to facilitate inspection or treatment surface, exterior surface or inside the ■ drains and foundation damp- This sheet summarizes key issues that builders, code perimeter wall, or the perimeter wall itself proofing or water-proofing to protect the Combustion Safety may provide the required R-value officials and consumers should keep in mind when structure from sub-surface water ■ Specification of direct-vent (“two-pipe”) ■ Insulation at the sub-floor installed without deciding how to design or install closed crawl spaces ■ Air sealing of the access , perimeter wall combustion appliances to ensure adequate gaps or compression and in full contact with in new construction. and perimeter framing to prevent the entry of combustion air for fuel-fired appliances, if the sub-floor to achieve nominal R-value moisture-laden outside air and to separate the applicable. Some manufacturers have direct- The second sheet provides two sample designs that ■ Non-porous insulation if the perimeter wall crawl space from areas under or decks vent cabinets for use with non-direct-vent is insulated have been field-tested and extensively monitored. ■ An access door that is protected from roof models. Alternate means of providing combustion air must be approved by the ■ Insulation on the crawl space access(es) of For more details and information on improving wall- runoff, at least 4" higher than the exterior minimum R-2 soil grade and made of a non-corroding appliance manufacturer and local residential vented crawl spaces in existing homes, visit material, especially in coastal communities code requirements. Radon Control ■ www.crawlspaces.org. ■ A fully sealed vapor retarder on the floor and For homes on slabs, or crawl ■ In areas where radon is a risk or where the perimeter to reduce evaporation of spaces, specification of carbon monoxide local residential code requires control of water into the crawl space monitors or alarms if the structure has radon or other soil gases, with an attached or any combustion closed crawl space foundations can be ■ Appliance discharge pipes and exhausts appliances from , and clothes dryers tested, monitored and, if necessary, ■ For homes on basements or crawl spaces, that terminate outside the crawl space mitigated with the same techniques used for optional specification of an appropriately houses with a slab or foundation ■ A mechanical drying system to reduce placed raw-gas leak alarm if fuel-fired in the same region. (for example, a supply of appliances or fuel lines are in the ■ The U.S. Environmental Protection Agency conditioned air or a ) and the Surgeon General recommend testing ■ Fire Safety Drains with backflow valves or sump pumps all homes for radon to remove liquid water from the crawl space ■ Air sealing of all penetrations in the sub- if necessary floor with non-porous materials ■ vents that minimize standby air ■ Documentation of fire-rating to allow leakage, when required installation of exposed foam insulation without a thermal barrier, if applicable ■ Documentation of fire-rating to allow installation of exposed facing or backing materials on batt insulation, if applicable

HIGH-PERFORMANCE HOMES A Quick Reference on Closed Crawl Spaces www.crawlspaces.org

INSTALLING CLOSED CRAWL SPACES

Choosing a design for a closed crawl space goes Recommended Strategies Additional Recommendations Quality Assurance Options hand-in-hand with the first steps required to for Avoiding Problems ■ install the closed crawl space: coordinating with Coordinate with your pest management Experienced installers care about the long-term code officials to ensure that your design meets Quality installers of closed crawl spaces know professional to ensure that the closed performance of their system and will usually local residential code requirements and obtaining that managing moisture during the process of crawl space system does not interfere with offer one or more of the following quality the required permits. At the time of this writing, construction is critical for success and will use their treatment or affect their warranty, assurance options with their closed crawl space the North Carolina Code Council has several strategies to avoid problems: if applicable system: adopted and the state of North Carolina has ■ Grading the crawl space floor surface to one ■ Mechanically fasten the liner material to the ■ A monitoring system to inform the homeowner approved new code language governing both or more low spots and installing a drain or perimeter wall in addition to sealing it to the of relative humidity levels in the crawl space wall-vented and closed crawl spaces. This new other method to remove water that enters the wall. Adhesives, sealants or tapes alone may ■ A water alarm to inform the homeowner of a code is available for reference as of January 1, crawl space prior to dry-in be insufficient to support the material. buildup of liquid water in the crawl space 2005, as an alternate to the existing printed code, ■ ■ Grading around the foundation as soon as Use duct mastic with embedded fiberglass ■ A posted sign informing anyone entering the and the new code will be enforced in 2006 with mesh tape to seal seams in crawl space vapor the release of the updated North Carolina possible to reduce the amount of roof runoff crawl space of the system components or ground surface water that enters the crawl retarder materials. If tapes or sealants are to maintaining the integrity of the system Residential Code. In some cases, local code be used, ensure that the product is accepted space ■ officials may require or accept a stamped letter of for use by the manufacturer of the material A repair kit for fixing small amounts of ■ Minimizing the amount of rainwater that can approval from a registered professional engineer and will provide long-term performance. damage to the vapor retarder after the house as an alternate path for permitting and inspection. enter the crawl space Regardless of the method, a quality installer is occupied ■ Quality installers ensure that their employees are Covering the crawl space floor with a will have a process in place to ensure proper ■ An annual monitoring service to replace trained in the use of the tools and materials temporary vapor retarder by the time the installation. batteries in monitoring systems and check that required to install their closed crawl space structure is dried-in. This temporary cover ■ Protect 6-mil un-reinforced polyethylene the crawl space system is in good working system and generally provide and/or require the must be removed before installation of the ground vapor retarders to avoid damage in order. This may include measurements of use of respirators and protective clothing for the finished ground vapor retarder. areas that will be accessed for servicing of wood moisture content or air tightness, or comfort and safety of their employees. Quality ■ Puncturing holes at low spots in the mechanical equipment. Thicker, reinforced download and analysis of data logging installers of closed crawl spaces will have temporary ground vapor retarder (if the ground polyethylene materials are more durable. equipment documented processes for coordinating with the is not saturated) to allow small puddles to ■ A guarantee that relative humidity will be general contractor and other building trades to drain into the ground maintained below an agreed-upon target ensure proper scheduling and to reduce the risk ■ Closing the access door(s) and running a (typically 70% or lower) over specified of damage to the closed crawl space system dehumidifier to remove accumulated moisture periods of time with exceptions for water leaks during construction. They also will explain any after the structure is dried-in or intrusion outside their control impact on pricing or scheduling of variable ■ References to independent third-parties for factors like the number of piers in a crawl ■ Coordinating with the construction site crew to quality assurance space, height above or below grade or ensure that the crawl space door is closed as complexity of the foundation footprint. much as possible, that all drains remain unblocked and that any have a power source, run long enough to provide the necessary drying and are protected from theft

Printed on 100% post-consumer recycled material HIGH-PERFORMANCE HOMES A Quick Reference on Closed Crawl Spaces www.crawlspaces.org DESIGN SAMPLE 1 7 A closed crawl space with supply air and floor insulation

8 1. Seal exterior wall penetrations and 9. Leave a minimum 3” termite inspection 1 mating surfaces at top and bottom of sill gap between the top of the wall vapor 9 plate and at top and bottom of band retarder and the top of the masonry wall. 2 3 joist. Crawl space access panel(s) or Seal the top of the vapor retarder to the Supply Trunk Duct door(s) must be air-sealed. wall with duct mastic or equivalent sealant. Optionally, apply a light colored 10 11 2. No open foundation vents are allowed in paint or coating over the inspection gap 4 12 exterior walls. Openings to ventilated to improve inspectability by pest control foundations must be air-sealed professionals. 14 13 with an access panel or permanent materials. Install flood vents per local 10. Air seal all heating and cooling ductwork residential code where required. with a mastic system. Install all ductwork located in the crawl space with R-value 3. Slope finished grade away from building per local code requirement. 5 per local residential code or for 6-inch 15 drop over 10 feet. Provide a method to 11. Control moisture vapor in the crawl space transport roof runoff away from the with supply air from the house air- house. Gutters and downspouts are one conditioning system. Set supply air 6 such method. volume per local residential code requirement. Adjust as needed to control 4. Dampproof or waterproof the exterior relative humidity in crawl space to desired wall surface when the crawl space floor level. Provide a backflow damper and Drawing not to scale is below exterior grade. either a balancing damper or constant 5. It is not necessary to provide a capillary airflow regulator to control airflow. break between the footings and Multiple supply vents may be used to combustion exhaust gases are piped 15. Grade the crawl space floor to one or foundation walls or interior . achieve the desired airflow and/or desired directly from the appliance to outside. more low points. Provide crawl space distribution of air. No return air vent is drain(s) or sump pump(s) at lowest 6. Provide foundation drain to daylight per allowed in the crawl space. 14. Cover 100% of the crawl space floor with point(s). Slope drains to daylight and local residential code requirements. a minimum 6-mil vapor retarder. Install include an accessible backflow valve and 12. Terminate water heater drains, vapor retarder material on the inside wall 1/4-inch rodent screening. Gutter drains 7. Seal all , electrical, duct, cable, temperature/pressure relief pipes, and surfaces, and mechanically fasten and and foundation drains (interior or exterior) and other penetrations through the A/C condensate drains to outdoors or to seal it to the top of the walls, leaving the must not be connected to the crawl sub-floor with fire-stop materials an interior pump that discharges to a required inspection gap. Extend the space drain. and sealants. Fiberglass or rockwool drain or outdoors. Terminate all , material up the interior columns at least insulation alone are not sufficient. and clothes dryer vents to 4 inches above the crawl space floor. outdoors. Seal all seams and edges with fiberglass 8. Insulate floor joist cavities. Place mesh tape and mastic or equivalent. insulation in full contact with the sub- 13. Any fuel-fired , water heaters, or Mechanically secure the vapor retarder to floor and ensure that it is secured in other appliance in a closed crawl space the ground as necessary. place. Use R-value required by local should be of a “direct vent” or "two pipe" residential code and install without gaps, design, meaning that all air for voids, or compression. combustion is piped directly from outside to the appliance and all

HIGH-PERFORMANCE HOMES A Quick Reference on Closed Crawl Spaces www.crawlspaces.org

DESIGN SAMPLE 2 7 A closed crawl space with supply air and wall insulation 8 1 1. Seal exterior wall penetrations and mating wall insulation and the crawl space floor 9 surfaces at top and bottom of sill plate surface. Obtain R-value from local 2 3 and at top and bottom of band joist. residential code. Ensure that the Supply Trunk Duct Crawl space access panel(s) or door(s) insulation complies with local residential 8 10 11 must be air-sealed. code requirements for installation without 4 a thermal barrier or ignition barrier. 12 2. No open foundation vents are allowed in Insulate the band joist with batt insulation 14 13 exterior walls. Openings to ventilated to facilitate removal and reinsertion during porch foundations must be air-sealed pest control inspections. Ensure that batt with an access panel or permanent facings comply with local fire materials. Install flood vents per local requirements. residential code where required. 5 15 9. Leave a minimum 3” termite inspection 3. Slope finished grade away from building gap between the top of the wall vapor per local residential code or for 6-inch drop retarder and the top of the masonry wall. 6 over 10 feet. Provide a method to transport Seal the top of the vapor retarder to the roof runoff away from the house. Gutters wall with duct mastic or equivalent and downspouts are one such method. sealant. Optionally, apply a light colored 4. Dampproof or waterproof the exterior wall paint or coating over the inspection gap Drawing not to scale surface when the crawl space floor is to improve inspectability by pest control below exterior grade. professionals. A/C condensate drains to outdoors or to material up the interior columns at least 10. Air seal all heating and cooling ductwork 5. It is not necessary to provide a capillary an interior pump that discharges to a 4 inches above the crawl space floor. Seal with a mastic system. Install all ductwork break between the footings and drain or outdoors. Terminate all kitchen, all seams and edges with fiberglass mesh located in the crawl space with R-value foundation walls or interior columns. bathroom, and clothes dryer vents tape and mastic or equivalent. per local code requirement. Mechanically secure the vapor retarder to 6. Provide foundation drain to daylight per to outdoors. the ground as necessary. local residential code requirements. 11. Control moisture vapor in the crawl space 13. Any fuel-fired furnaces, water heaters, or with supply air from the house air- other appliance in a closed crawl space 15. Grade the crawl space floor to one or more 7. Seal all plumbing, electrical, duct, conditioning system. Set supply air volume should be of a “direct vent” or “two pipe” low points. Provide crawl space drain(s) or cable, and other penetrations through the per local residential code requirement. design, meaning that all air for sump pump(s) at lowest point(s). Slope sub-floor with fire-stop materials Adjust as needed to control relative combustion is piped directly from outside drains to daylight and include an and sealants. Fiberglass or rockwool humidity in crawl space to desired level. to the appliance and all combustion accessible backflow valve and 1/4-inch insulation alone are not sufficient. Provide a backflow damper and either a exhaust gases are piped directly from the rodent screening. Gutter drains and balancing damper or constant airflow appliance to outside. 8. Insulate the crawl space wall over the wall foundation drains (interior or exterior) must regulator to control airflow. Multiple supply not be connected to the crawl space drain. vapor retarder material with rigid foam or vents may be used to achieve the desired 14. Cover 100% of the crawl space floor with other non-porous insulation material. airflow and/or desired distribution of air. No a minimum 6-mil vapor retarder. Install Leave a minimum 3” termite inspection return air vent is allowed in the crawl space. vapor retarder material on the inside wall gap between the top of the wall insulation surfaces, and mechanically fasten and and the top of the masonry wall. Leave a 12. Terminate water heater drains, seal it to the top of the walls, leaving the 3” wicking gap between the bottom of the temperature/pressure relief pipes, and required inspection gap. Extend the

Printed on 100% post-consumer recycled material HIGH-PERFORMANCE HOMES