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University of Waterloo www.civil.uwaterloo.ca/beg
John Straube Presentation 1
Building Better Basements, or“How to Build Basements that Don’t Stink”
www.BalancedSolutions.comwww.civil.uwaterlo.ca\beg
BEGBuilding Engineering Group
Dr John StraubeAssistant ProfessorDupont Young Professor
University of Waterloo
1/31/2005 John Straube2 /71
1/31/2005 John Straube3 /71
This presentation
Basements– How are they changing– What they do
Performance– Problems– Causes
Solutions
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Basements are Changing
Increasingly used as living space– Not a root cellar anymore!– High quality space expected - new and retrofit– Owner can finish herself– Low cost for high density sites (cities)– Can now locate laundry, heating, hotwater elsewhere– Slabs growing (old people) unlikely to make a major dent
Modern basements are different – they need different approaches!
University of Waterloo www.civil.uwaterloo.ca/beg
John Straube Presentation 2
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Basements – Part of the Enclosure
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Basements
Below grade enclosure– Includes floor slabs, and practically rim joist– Separates exterior (soil/air) and interior
Functions of all parts of the enclosure– Support– Control– Finish (usually)
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Functions of the building enclosure
Support – Structure: wind, gravity, earthquake– Below grade – Soil pressure, hydrostatic?
Control– Heat (less extreme than above grade)– Air (less air pressure, but it stinks, Radon?)– Moisture (vapor, free and bound liquid)
Finish – usually, but optionalDistribute (sometimes)
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Support (Structural performance)
Structural system– Does not work based on rational analysis– Don’t ask for an engineers stamp
Failure modes– Poorly compacted subsoil– Top-edge Bracing
Raised bungalowsStairwells parallel to wall
University of Waterloo www.civil.uwaterloo.ca/beg
John Straube Presentation 3
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Basement Structural System
Foundation Wall
Floor slab
Footing
Above Grade
Below Grade
Similar for Similar for most most basementsbasements
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Basement Structural System
Floor slab
Footing
Above Grade
Below Grade
••Raised BungalowsRaised Bungalows•• StairsStairs
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Control: Moisture
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
Where does moisture come from?– Exterior– Interior– Built in
Recent studies – Minn, Chicago, CMHC, IRC
University of Waterloo www.civil.uwaterloo.ca/beg
John Straube Presentation 4
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Exterior surface Exterior surface waterwater
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Surface Drainage
First step– Common problem
OverhangEavestroughDownspoutsSloped gradePerimeter drain
From: Lstiburek 2002
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Exterior surface waterExterior surface water••Drainage wont help hereDrainage wont help here••Damage recoveryDamage recovery
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Moisture Sources:
built into the Assembly
•Minimize by:• Delay finishing internally• Reduce water in concrete
1. Built-in Moisture (from water in concrete, mortar, wood, etc.)
2. Construction moisture accumulated during construction (ice, snow, rain, etc.)
1. & 2.
1. & 2.
University of Waterloo www.civil.uwaterloo.ca/beg
John Straube Presentation 5
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Initial Drying
From: Lstiburek 2002
Soil cold for first yrExcavation collects waterConcrete is wet
– 25-50 liters/m2
Cannot dry to wet exteriorSolutions = dry in
– No low perm interior– Semi-permeable insulation– Smart vapor barrier
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Basement in a Bag• Tolerable north of Arctic Circle
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Moisture Sources:
from Exterior Environment
Minimize Rain loadsProvide Good SheddingProvide Good DrainageProvide Capillary Breaks
3. Surface water Run-off
2. Rainwater shedding
1. Precipitation
5. Sub-surface Moisture - Groundwater- Vapor
4. Water vapor
5. Sub-surface Moisture 5. 1/31/2005 John Straube20 /71
A wet basement – ground water
University of Waterloo www.civil.uwaterloo.ca/beg
John Straube Presentation 6
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Controlling ground/rain water
Many different acceptable methodsClassification of Groundwater control
– 1. DrainedNeeds capillary break and gap/drain space
– 2. Perfect BarrierOne layer of perfect water resistanceBeware hydrostatic forces
– 3. Storage (mass) Safe storage capacity and dryingDon’t use vapor barriers, do insulate (carefully)
Exterior Moisture
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Drainage by specific backfill soil properties
Screened(1) Below-Grade Enclosure Wall System
Collection and Exit Drain
Interface with undisturbed below grade environment
Above Grade Level
Below Grade Level
A. Screen (similar to cladding---shed and screen surface moisture-rain)
B. Drainage–crushed stone
C. Drainage plane and
Capillary break
E. Concrete or concrete masonry
F. Insulation (int. option)
G. Interior finish
Drained type:• drainage system with drainage plane, and• capillary break
B. Drainage– draining backfill
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Screened(2) Below-Grade Enclosure Wall System
Collection and Removal Drain
Interface with undisturbed below-grade environment
Above Grade Level
Below Grade Level
A. Screen -optional (similar to cladding---shed and screen surface moisture-rain)
C. Drainage plane and
Capillary break
E. Concrete or concrete masonry
F. Insulation (int. option)
G. Interior finish
Drained type:• drainage system with drainage layer& plane,• capillary break
Backfill – not necessarily free draining
Non-soil drainage layer
B. Drainage–crushed stone
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Screened(3) Below-Grade Enclosure Wall System
Collector and Removal Drain
Interface with undisturbed below grade environment
Above Grade Level
Below Grade Level
A. Screen – optional (similar to cladding---shed and screen liquid moisture-rain and groundwater)
C. Drainage plane and
Capillary break
E. Concrete or concrete masonry
F. Insulation (int. option)
G. Interior finish
Drained type:• drainage system with drainage plane, and• capillary break
B. Backfill – not necessarily free draining
Interior Drainage(often retrofit)
B. Drainage–crushed stone
University of Waterloo www.civil.uwaterloo.ca/beg
John Straube Presentation 7
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Barrier (1) Below-Grade Enclosure Wall System
Collector and Removal Drain
Interface with undisturbed below grade environment
Above Grade Level
Below Grade Level
A. Screen – optional(similar to cladding---shed and screen surface moisture-rain)
B. Drainage (opt) – crushed stone
A. Positive side Waterproofing
B. Concrete or masonry
C. Insulation—heat flow control (int. option)
D. Interior finish
Perfect barrier:• drainage system needed to reduce hydrostatic pressure• waterproofing layer resists 300-600 mm head of water
Backfill – not necessarily free draining
No Drainage – hydrostatic pressure developed
Lowers water table, reduces hydrostatic pressure 1/31/2005 John Straube26 /71
Barrier (2) Below-Grade Enclosure Wall System
Collector and Exit Drain
Interface with undisturbed below grade environment
Above Grade Level
Below Grade Level
A. Screen – optional(similar to cladding---shed and screen surface moisture-rain)
B. Drainage (opt) –crushed stone
A. Negative side Waterproofing
B. Concrete or concrete masonry
C. Insulation—heat flow retarder (int. option)
D. Interior finish
Perfect barrier :• drainage system to reduce hydrostatic pressure• waterproofing
Backfill – not necessarily free draining
No Drainage – hydrostatic pressure developed
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Storage (1) Below-Grade Enclosure Wall System
Collector and Removal Drain
Interface with undisturbed below grade environment
Above Grade Level
Below Grade Level
A. Screen – optional(similar to cladding---shed and screen surface moisture-rain)
B. Drainage (opt) –crushed stone
A. Rubble or concrete masonry (storage)
B. Usually no insulation to allow drying
C. Usually no interior finish (limewash)
Storage (mass) system:• usually no intentional drainage• often no capillary break
Backfill – not necessarily free draining
Limited ability to resist moisture loads
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Damproofing• Capillary break = drainage plane, but needs gap• vapour barrier?•NOT waterproofing
University of Waterloo www.civil.uwaterloo.ca/beg
John Straube Presentation 8
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GlassfiberGlassfiber Drainage LayerDrainage Layer
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R k l D i L
RockwoolRockwool Drainage LayerDrainage Layer
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Dimple Sheets
Drainage gapact as vapor barrierSo little water = maybe no capillary break needed
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Controlling ground/rain water
Roof and Surface DrainageClassification of Groundwater control
– 1. DrainedNeeds capillary break & gap/drain space
– 2. Perfect BarrierOne layer of perfect water resistanceBeware hydrostatic forces
– 3. Storage (mass) Safe storage capacity and dryingDon’t use vapor barriers, do insulate (carefully)
Perimeter Drains
Exterior Moisture
University of Waterloo www.civil.uwaterloo.ca/beg
John Straube Presentation 9
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Moisture Sources:
from Interior
1. Water Vapor
2. Localized Flooding (abnormal - Water & Vapor)
3. Localized Flooding(Abnormal)
Control interior vapor levels by:• winter ventilation• summer dehumidcation
Control flooding• floor drains• disaster pans at appliances
2.
3.
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Air and vapor
Surface condensationInterstitial condensationSolar driven summer condensationDrying retardersPsychrometric Chart
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Special Exterior Conditions
Exterior soil is almost always at 100%RH– Plus liquid water can press against wall
Never gets as cold or as hot as above gradeSignificant vertical temperature gradients– Top is different than bottom
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Moisture – not ground water
University of Waterloo www.civil.uwaterloo.ca/beg
John Straube Presentation 10
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Measured Soil Temperatures
-5
0
5
10
15
20
25
Jan Feb Mar April May June July Aug Sept Oct Nov Dec
Date
Tem
pera
ture
(C)
0.1 m
0.5 m
1.0 m
3 m
2.0 m
Note: open field values. No house to add heat
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Measured Soil Temperatures
5 10 15 20 25
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Soil Temperatures at University of Waterloo Weather Station (1999)
-5
0
5
10
15
20
25
30
0 4 8 12 16 20 24 28 32 36 40 44 48 52
Time (weeks from January)
Tem
pera
ture
(C)
soil temp (50 mm)soil temp (200 mm)
Waterloo Measured Soil Temperatures
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Exterior Temperature and Moisture Conditions
• Soil Relative Humidity almost always =100%
• Liquid water may be present
Temperature200 10
SummerJuly
WinterJan.
University of Waterloo www.civil.uwaterloo.ca/beg
John Straube Presentation 11
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Temperature ( °C)
0
500
1000
1500
2000
2500
3000
3500
4000
Vap
our
Pre
ssure
(Pa
)
100% RH75% RH50% RH25% RH
Psych Chart: Air Vapour Content vs Temperature
Saturation
50%
RH
25%RH
75%
RH
100%
RH
100%RH
Temperature
Air
Moi
stur
e C
onte
nt
= va
pour
pres
sure
(Pa,
in H
g),
hum
idity
rat
io (g
/kg,
gra
ins/
pd)
-10 ºC14 º F
0 ºC32 º F
10 ºC50 º F
20 ºC68 º F
30 ºC86 º F
40 ºC104º F
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Basement Vapour Movement
Vapor moves by Diffusion & Air movementDiffusion
Water vapor moves from more to lessCommon rule:– place vapor retarding layers on moist (i.e. high
vapor pressure) side to control vapor diffusionAir Leakage
Vapor moves with air flow (high to low pressure)– Stop air flow or flow from dry side
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Temperature ( °C)
0
500
1000
1500
2000
2500
3000
3500
4000
Vap
our
Pre
ssure
(Pa
)
100% RH75% RH50% RH25% RH
Below Grade Basement Psychrometrics
Summer
Winter
-10 ºC14 º F
0 ºC32 º F
10 ºC50 º F
20 ºC68 º F
30 ºC86 º F
40 ºC104º F
Since soil is at nearly 100%RH, the vapor drive is almost always inward except at very top during winter in humid houses
Janu
ary
top
foot
ing
July
foot
ing
top
Flow out
Flow in
Flow in
University of Waterloo www.civil.uwaterloo.ca/beg
John Straube Presentation 12
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Basement Vapour Diffusion
Water vapor is moving from soil to interior – for almost the entire year – over all but the top foot of basement
Hence, place vapor barrier on outsideBut we put it on the inside!Moisture moving by diffusion from drying concrete and soil is trapped by interior vapor barriers
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Air M
oist
ure
Con
tent
Air
Moi
stur
e C
onte
ntTe
mpe
ratu
re
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Basement Air Movement
Water vapor moves along with airflowIf moist air touches a cold surface, condensation occursControl?– Include an air barrer– Avoid air loops– Avoid pressures
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Condensation: Cool air contains less vapor
Cool air – increase RHHeat air – decrease RH
University of Waterloo www.civil.uwaterloo.ca/beg
John Straube Presentation 13
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Air leakage
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Internal Stack Effect & Insulation
Hot air = lightHot air = light
Cold air = heavy
• Gaps in batt insulation on both sides•Wrinkles inevitable
Air gapsBatt
Inside
OutsideCommon basement problem
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Internal Stack Effect
Cold WeatherCold WeatherHot air = lightHot air = light
Cold air = heavyCold air = heavy
Result: Air Result: Air FlowFlow
• Gaps in batt insulation on both sides
• closed circuit
• energy cost
• cold surfaces
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Air movement (Stack Effect)
Cold concrete = summer & winterCold concrete = summer & winter
Result: Air Result: Air FlowFlow
Hot air = lightHot air = light
Cold air = heavyCold air = heavy
University of Waterloo www.civil.uwaterloo.ca/beg
John Straube Presentation 14
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Wall w/ only Batt Insulation
Air leakageAir leakage
Air permeable Air permeable insulationinsulation
CrackCrack
Cold
Condensation
Winter
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Wall w/ Insulated Sheathing
Air leakageAir leakage
Air permeable Air permeable insulationinsulation
CrackCrack
Warmer
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Materials to use?
Foam Board: EPS, XPS, PIC– water tolerant– vapour barriers to vapour retarders
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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ICFs
If you afford it, use them – cap break, insulation, vapor retarder
University of Waterloo www.civil.uwaterloo.ca/beg
John Straube Presentation 15
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Better
Add layer of:– foam or– spray
foam
Insulation & service distribution space
2x framing
Gypsum wallboard
Plastic baseboard
Keep bottom of drywall ¾" off of finished floorInstall capillary break or ½" plastic wood spacer under bottom plate
pre-manufactured drainage layer (shown) or free draining material
Site sloped away from building
Urethane foam airsealSill gasket air seal
Poly vapor barrier
Continuous sealant joint over bond break
Damproofing
Sealant airseal
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Best?Insulation & service
distribution space
Gypsum wallboard
Plastic baseboard
Keep bottom of drywall ¾" off of finished floor
Draintile in crushed stone wrapped in geotextile
pre-manufactured drainage layer (shown) or free draining material
Site sloped away from building
Urethane foam airsealSill gasket air seal
Poly vapor barrier
Continuous sealant joint over bond break
Damproofing
1x2 horizontal strapping
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Foam onlyVertical strapping
University of Waterloo www.civil.uwaterloo.ca/beg
John Straube Presentation 16
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Solar Drives at Grade
Wet concrete from rain, grade, built-inSun shines on wall and heats itWater evaporates and diffuses in & outCan condense inside of cold and impermeable
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2.Vapour drives inward (& out) 3.Condensation
on “cold”surfaces
1. Temperature and solar heating
warms wet material
WettingIf impermeable
DryingIf permeable
3.Vapour dries to inside
Inward Diffusion @ grade
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Temperature ( °C)
0
500
1000
1500
2000
2500
3000
3500
4000V
ap
our
Pre
ssure
(Pa
)
100% RH75% RH50% RH25% RH
Hot Wet materials
• 30-60 C• 90-100% RH•VERY high vapour pressure
SummerWinter
-10 ºC14 º F
0 ºC32 º F
10 ºC50 º F
20 ºC68 º F
30 ºC86 º F
40 ºC104º F 1/31/2005 John Straube64 /71
Rim joists
Scenario– Wood generally on exterior– 38 mm Wood is a vapor barrier– Practically difficult to stop air leakage
Result– Condensation on rim joist in cold weather– Decay if it can’t dry in or out
Solutions– Insulate on exterior
University of Waterloo www.civil.uwaterloo.ca/beg
John Straube Presentation 17
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Basement Floors
Basement floors – Part of enclosure
Concrete alone fine but when you finish…– Comfort (cold and hard)– Water under finish flooring– Water condensing on top (summer)
Solutions– Install finish over small amount of insulation– Install vapor barrier
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Slabs
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Summary
TolerableRiskyBe perfect..& lucky
University of Waterloo www.civil.uwaterloo.ca/beg
John Straube Presentation 18
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Summary
good
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Summary-best
best
From: Lstiburek 2002
This is theoretically best, but thermal mass of walls requires good summer humidity control and floor should be insulated
Insulation & service distribution space
Gypsum wallboard
Plastic baseboard
Keep bottom of drywall ¾" off of finished floor
Draintile in crushed stone wrapped in geotextile
pre-manufactured drainage layer (shown) or free draining material
Site sloped away from building
Urethane foam airsealSill gasket air seal
Poly vapor barrier
Continuous sealant joint over bond break
Damproofing
1x2 horizontal strapping
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Conclusions
Building in a hole in the ground is hardDon’t forget about built-in moistureand remember summerMoisture comes in liquid AND vapor Insulation and drainage are the best tools, not vapor barriers and waterproofing
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1/31/2005 John Straube72 /71
Addition
Repair– Wall leaks groundwater
Retrofit/Reno– Risk reduction