University of Waterloo www.civil.uwaterloo.ca/beg
Building Better Basements, or “How to Build Basements that Don’t Stink”
Dr John Straube Assistant Professor Dupont Young Professor
University of Waterloo
www.BalancedSolutions.com BEG www.civil.uwaterlo.ca\beg Building Engineering Group 2 /71 1/31/2005 John Straube
This presentation Basements are Changing
z Basements z Increasingly used as living space – Not a root cellar anymore! – How are they changing – High quality space expected - new and retrofit – What they do – Owner can finish herself – Low cost for high density sites (cities) z Performance – Can now locate laundry, heating, hotwater elsewhere – Problems – Slabs growing (old people) unlikely to make a major dent
– Causes z Modern basements are different – they need different approaches! z Solutions
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John Straube Presentation 1 University of Waterloo www.civil.uwaterloo.ca/beg
Basements – Part of the Enclosure Basements
z z Below grade enclosure – Includes floor slabs, and practically rim joist – Separates exterior (soil/air) and interior z Functions of all parts of the enclosure – Support – Control – Finish (usually)
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Functions of the building enclosure Support (Structural performance)
z Support z Structural system – Structure: wind, gravity, earthquake – Does not work based on rational analysis – Below grade – Soil pressure, hydrostatic? – Don’t ask for an engineers stamp z Control z Failure modes – Heat (less extreme than above grade) – Poorly compacted subsoil – Air (less air pressure, but it stinks, Radon?) – Top-edge Bracing – Moisture (vapor, free and bound liquid) z Raised bungalows z Finish – usually, but optional z Stairwells parallel to wall z Distribute (sometimes)
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John Straube Presentation 2 University of Waterloo www.civil.uwaterloo.ca/beg
Basement Structural System Basement Structural System
Similar for •Raised Bungalows most • Stairs Above Grade basements
Below Grade Foundation Wall Above Grade
Below Grade
Floor slab Floor slab Footing Footing
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Control: Moisture
z Moisture causes most failures (less spectacular) – Mold (musty smell) – Decay (especially rim joist) – Staining /Paint peeling – Floods and leaks, eventually causing the above – Salt damage to masonry – old basements z Where does moisture come from? – Exterior – Interior – Built in z Recent studies – Minn, Chicago, CMHC, IRC
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John Straube Presentation 3 University of Waterloo www.civil.uwaterloo.ca/beg
From: Lstiburek 2002 Exterior surface water Surface Drainage
z First step – Common problem z Overhang z Eavestrough z Downspouts z Sloped grade z Perimeter drain
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Moisture Sources:
built into the Assembly 1. Built-in Moisture (from water in concrete, mortar, wood, etc.)
2. Construction moisture accumulated during construction (ice, snow, rain, etc.)
•Minimize by: • Delay finishing internally 1. & 2. Exterior surface water • Reduce water in concrete •Drainage wont help here
•Damage recovery 1. & 2. 15 /71 1/31/2005 John Straube 16 /71 1/31/2005 John Straube
John Straube Presentation 4 University of Waterloo www.civil.uwaterloo.ca/beg
Initial Drying
z Soil cold for first yr z Excavation collects water z Concrete is wet From: Lstiburek 2002 – 25-50 liters/m2 z Cannot dry to wet exterior z Solutions = dry in – No low perm interior – Semi-permeable insulation – Smart vapor barrier
Basement in a Bag • Tolerable north of Arctic Circle 17 /71 1/31/2005 John Straube 18 /71 1/31/2005 John Straube
Moisture Sources: 1. Pre cipitation 2. Rainwater shedding 4. Water vapor 3. Surface water Run-off from Exterior Environment
5. Sub-surface Moisture - Groundwater - Vapor
Minimize Rain loads Provide Good Shedding Provide Good Drainage Provide Capillary Breaks A wet basement 5. Sub-surface Moisture 5. 19 /71 1/31/2005 John Straube 20 /71 1/31/2005 – ground waterJohn Straube
John Straube Presentation 5 University of Waterloo www.civil.uwaterloo.ca/beg
Exterior Moisture Screened(1) Below-Grade Enclosure Wall System Drained type: • drainage system with drainage plane, and Controlling ground/rain water Drainage by specific • capillary break backfill soil properties Above Grade Level A. Screen (similar to cladding---shed z Many different acceptable methods and screen surface moisture-rain)
z Classification of Groundwater control Below Grade Level C. Drainage plane and – 1. Drained z Needs capillary break and gap/drain space Capillary break B. Drainage– draining – 2. Perfect Barrier E. Concrete or backfill z One layer of perfect water resistance concrete masonry z Beware hydrostatic forces Interface with undisturbed F. Insulation (int. below grade environment – 3. Storage (mass) option) z Safe storage capacity and drying G. Interior finish z Don’t use vapor barriers, do insulate (carefully) B. Drainage– crushed stone
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Screened(2) Below-Grade Enclosure Wall System Screened(3) Below-Grade Enclosure Wall System
Drained type: Drained type: • drainage system with drainage layer& plane, • drainage system with drainage plane, and • capillary break Interior Drainage • capillary break Non-soil drainage layer (often retrofit) Above Grade Level Above Grade Level A. Screen -optional (similar to A. Screen – optional (similar to cladding---shed and screen surface cladding---shed and screen liquid moisture-rain) moisture-rain and groundwater) Below Grade Level C. Drainage plane and C. Drainage plane and Below Grade Level Capillary break Capillary break Backfill – not necessarily B. Backfill – not necessarily free draining free draining E. Concrete or E. Concrete or concrete masonry concrete masonry Interface with undisturbed Interface with undisturbed F. Insulation (int. below-grade environment F. Insulation (int. below grade environment option) option) G. Interior finish G. Interior finish
B. Drainage– B. Drainage– crushed stone crushed stone
23 /71 24 /71 1/31/2005 Collection andJohn Removal Straube Drain 1/31/2005 Collector and RemovalJohn Straube Drain
John Straube Presentation 6 University of Waterloo www.civil.uwaterloo.ca/beg
Barrier (1) Below-Grade Enclosure Wall System Barrier (2) Below-Grade Enclosure Wall System
Perfect barrier: Perfect barrier : • drainage system needed to reduce hydrostatic pressure • drainage system to reduce hydrostatic pressure No Drainage – hydrostatic • waterproofing layer resists 300-600 mm head of water No Drainage – hydrostatic • waterproofing pressure developed pressure developed Above Grade Level Above Grade Level A. Screen – optional A. Screen – optional (similar to cladding---shed and (similar to cladding---shed and screen surface moisture-rain) screen surface moisture-rain) Below Grade Level Below Grade Level A. Positive side A. Negative side Waterproofing Waterproofing B. Concrete or B. Concrete or Backfill – not necessarily Backfill – not necessarily masonry free draining concrete masonry free draining C. Insulation—heat C. Insulation—heat flow control Interface with undisturbed below flow retarder (int. Interface with undisturbed below (int. option) grade environment option) grade environment D. Interior finish D. Interior finish
B. Drainage (opt) B. Drainage (opt) – – crushed stone crushed stone Lowers water table, reduces Collector and hydrostatic pressure 25 /71 1/31/2005 John Straube 26 /71 1/31/2005 John Straube Removal Drain Collector and Exit Drain
Storage (1) Below-Grade Enclosure Wall System
Storage (mass) system: • usually no intentional drainage Limited ability to resist • often no capillary break moisture loads Above Grade Level A. Screen – optional (similar to cladding---shed and screen surface moisture-rain) Below Grade Level A. Rubble or concrete masonry (storage) B. Usually no Backfill – not necessarily insulation to allow free draining drying C. Usually no interior finish (limewash) Damproofing • Capillary break = drainage plane, but needs gap Interface with undisturbed below • vapour barrier? grade environment •NOT waterproofing
B. Drainage (opt) – crushed stone
27 /71 28 /71 1/31/2005 Collector and RemovalJohn Straube Drain 1/31/2005 John Straube
John Straube Presentation 7 University of Waterloo www.civil.uwaterloo.ca/beg
Rockwool Drainage Layer Glassfiber Drainage Layer
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Exterior Moisture Dimple Sheets Controlling ground/rain water z Drainage gap z act as vapor barrier z Roof and Surface Drainage z So little water = maybe no z Classification of Groundwater control capillary break needed – 1. Drained z Needs capillary break & gap/drain space – 2. Perfect Barrier z One layer of perfect water resistance z Beware hydrostatic forces – 3. Storage (mass) z Safe storage capacity and drying z Don’t use vapor barriers, do insulate (carefully) z Perimeter Drains
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John Straube Presentation 8 University of Waterloo www.civil.uwaterloo.ca/beg
3. Localized Flooding Moisture Sources: 3. (Abnormal) Air and vapor
from Interior z Surface condensation Control interior vapor levels by: • winter ventilation z Interstitial condensation 1. Water Vapor • summer dehumidcation Control flooding z Solar driven summer condensation • floor drains • disaster pans at appliances z Drying retarders 2. Localized Flooding (abnormal - Water & z Psychrometric Chart Vapor) 2.
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Special Exterior Conditions Moisture – not ground water
z Exterior soil is almost always at 100%RH
– Plus liquid water can press against wall
z Never gets as cold or as hot as above grade
z Significant vertical temperature gradients
– Top is different than bottom
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John Straube Presentation 9 University of Waterloo www.civil.uwaterloo.ca/beg
Measured Soil Temperatures Measured Soil Temperatures
25
5 10 15 20 25 20 0.1 m
0.5 m
15 1.0 m
3 m
2.0 m 10 Temperature (C) 5 Note: open field values. No house to add heat
0 Jan Feb Mar April May June July Aug Sept Oct Nov Dec
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Exterior Temperature and Moisture Waterloo Measured Soil Temperatures Soil Temperatures at University of Waterloo Weather Station (1999) Conditions
30
soil temp (50 mm) soil temp (200 mm) 25
20 Summer July
15 • Soil Relative Humidity
10 almost always =100%
Temperature (C) • Liquid water may be Winter present 5 Jan.
0 0 4 8 1216202428323640444852
-5 Temperature Time (weeks from January) 010 20 39 /71 1/31/2005 John Straube 40 /71 1/31/2005 John Straube
John Straube Presentation 10 University of Waterloo www.civil.uwaterloo.ca/beg
Psych Chart: Air Vapour Content vs Temperature
Temperature H R
% 0 0 1
H R 40 00 % Saturation 5 7 35 00
H R 30 00 % 0 5 25 00 Vapour Pressure (Pa) Pressure Vapour Air Moisture Content RH 20 00 % = vapour pressure (Pa, in Hg), 5 humidity ratio (g/kg, grains/pd) 2 15 00
10 00 RH 100% 50 0 100% RH 75% RH 50% RH 25% RH 0 -10-10.0 ºC -5.00 ºC 0.010 5.0ºC 10.020 ºC 15.030 ºC 20.0 25.040 ºC 30.0 35.0 40.0 41 /71 42 /71 1/31/2005 John Straube 14 º F 32 º1/31/2005 F 50 º F 68 ºTem F p erJohn at ur eStraube ( °C) 86 º F 104º F
Below Grade Basement Psychrometrics Since soil is at nearly 100%RH, the vapor drive is almost always inward Basement Vapour Movement except at very top during winter in humid houses
40 00 z Vapor moves by Diffusion & Air movement top Diffusion 35 00
30 00 z Water vapor moves from more to less Flow in July
z Common rule: 25 00
– place vapor retarding layers on moist (i.e. high (Pa) Pressure Vapour Flow in Summer 20 00 vapor pressure) side to control vapor diffusion footing footing footing Air Leakage 15 00 January 10 00 z Vapor moves with air flow (high to low top Flow out pressure) Winter 50 0 100% RH 75% RH – Stop air flow or flow from dry side 50% RH 25% RH 0 -10- 10.0 ºC -5.00 ºC 0.010 ºC 5.0 10.020 ºC 15.030 ºC 20.0 25.040 ºC 30.0 35.0 40.0 43 /71 1/31/2005 John Straube 4414/71 º F 32 º1/31/2005 F 50 º F 68 º FTem perJohn at ur Straube e ( °C) 86 º F 104º F
John Straube Presentation 11 University of Waterloo www.civil.uwaterloo.ca/beg
Basement Vapour Diffusion
z Water vapor is moving from soil to Temperature
interior Air Moisture Content – for almost the entire year – over all but the top foot of basement z Hence, place vapor barrier on outside z But we put it on the inside! z Moisture moving by diffusion from drying concrete and soil is trapped by interior Content Moisture Air vapor barriers
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Condensation: Cool air contains less vapor Basement Air Movement Cool air – increase RH Heat air – decrease RH z Water vapor moves along with airflow z If moist air touches a cold surface, condensation occurs z Control? – Include an air barrer – Avoid air loops – Avoid pressures
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John Straube Presentation 12 University of Waterloo www.civil.uwaterloo.ca/beg
Air leakage
Internal Stack Effect & Insulation
• Gaps in batt insulation Inside on both sides Hot air = light •Wrinkles inevitable Hot air = light
Batt Air gaps
Cold air = heavy Outside Common basement problem
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Internal Stack Effect Air movement (Stack Effect)
• Gaps in batt Cold Weather Cold concrete = summer & winter insulation on Hot air = light both sides Hot air = light • closed circuit Result: Air • energy cost Flow Result: Air • cold surfaces Flow
Cold air = heavy Cold air = heavy
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John Straube Presentation 13 University of Waterloo www.civil.uwaterloo.ca/beg
Wall w/ only Batt Insulation Wall w/ Insulated Sheathing
Winter Cold Warmer Condensation Air permeable Air permeable insulation insulation
Air leakage Air leakage
Crack Crack
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Materials to use? ICFs
z Foam Board: EPS, XPS, PIC z If you afford it, use them – cap break, – water tolerant insulation, vapor retarder – vapour barriers to vapour retarders z spray foam – Semi-rigid (Icynene) and rigid (Spray polyurethane) – airtight – May allow some drainage – R values of 4 to 4.4/inch – vapour semi-permeable (Icynene much more)
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John Straube Presentation 14 University of Waterloo www.civil.uwaterloo.ca/beg
Site sloped away Sill gasket air seal from building Urethane foam airseal Better Sealant airseal Gypsum wallboard
Insulation & service z Add layer distribution space of: 2x framing Keep bottom of drywall pre-manufactured – foam or ¾" off of finished floor drainage layer Install capillary break or (shown) or free – spray ½" plastic wood spacer draining material foam under bottom plate Continuous sealant joint over bond break Damproofing Plastic baseboard
Poly vapor barrier
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Site sloped away Sill gasket air seal from building Urethane foam airseal
Best? 1x2 horizontal strapping Gypsum wallboard
Insulation & service distribution space z Foam only z Vertical pre-manufactured Keep bottom of drywall drainage layer strapping ¾" off of finished floor (shown) or free draining material
Continuous sealant joint over bond break Damproofing Plastic baseboard
Poly vapor barrier
59 /71 Draintile in crushed stone 60 /71 1/31/2005 wrappedJohn in geotextileStraube 1/31/2005 John Straube
John Straube Presentation 15 University of Waterloo www.civil.uwaterloo.ca/beg
Solar Drives at Grade Inward Diffusion @ grade
z Wet concrete from rain, grade, built-in Drying z Sun shines on wall and heats it If permeable z Water evaporates and diffuses in & out 1. Temperature 3.Vapour dries and solar heating to inside z Can condense inside of cold and warms wet impermeable material Wetting If impermeable 2.Vapour drives 3.Condensation inward (& out) on “cold” surfaces
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Hot Wet materials Rim joists
• 30-60 C 40 00 • 90-100% RH z Scenario •VERY high vapour pressure 35 00 – Wood generally on exterior
30 00 – 38 mm Wood is a vapor barrier – Practically difficult to stop air leakage 25 00 z Result
Vapour Pressure (Pa) Pressure Vapour 20 00 – Condensation on rim joist in cold weather Summer 15 00 – Decay if it can’t dry in or out Winter 10 00 z Solutions
50 0 – Insulate on exterior 100% RH 75% RH 50% RH 25% RH 0 -10-10.0 ºC -5.00 ºC 0.010 5.0 ºC 10.020 ºC 15.0 20.030 ºC 25.040 ºC 30.0 35.0 40.0 63 /71 Tem p er at ur e ( °C) 64 /71 14 º F 32 º1/31/2005 F 50 º F 68 º F John Straube86 º F 104º F 1/31/2005 John Straube
John Straube Presentation 16 University of Waterloo www.civil.uwaterloo.ca/beg
Basement Floors
z Basement floors – Part of enclosure z Concrete alone fine but when you finish… – Comfort (cold and hard) – Water under finish flooring – Water condensing on top (summer) z Solutions – Install finish over small amount of insulation – Install vapor barrier
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Slabs Summary
z Tolerable z Risky z Be perfect ..& lucky
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John Straube Presentation 17 University of Waterloo www.civil.uwaterloo.ca/beg
Site sloped away Sill gasket air seal from building Urethane foam airseal
1x2 horizontal strapping Summary Summary-best Gypsum wallboard Insulation & service distribution space
z good z best pre-manufactured Keep bottom of drywall drainage layer ¾" off of finished floor (shown) or free draining material
Continuous sealant joint over bond break Damproofing Plastic baseboard
From: Lstiburek 2002
Poly vapor barrier
Draintile in crushed stone wrapped in geotextile This is theoretically best, but thermal mass of walls requires good summer humidity control and floor should be insulated 69 /71 1/31/2005 John Straube 70 /71 1/31/2005 John Straube
Conclusions Addition
z Building in a hole in the ground is hard z Repair z Don’t forget about built-in moisture – Wall leaks groundwater z and remember summer z Retrofit/Reno z Moisture comes in liquid AND vapor – Risk reduction z Insulation and drainage are the best tools, not vapor barriers and waterproofing
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John Straube Presentation 18