basements are changing - building science corporation€¦ · basements no. 32/73 soil temperatures...
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Basements: New & Retrofit Energy Efficient, Durable, Healthy
John Straube, Ph.D., P.Eng
presented by www.buildingscience.com
Building Science Corporation
www.BuildingScience.com Basements No. 2/73
Basements are Changing
• Increasingly used as living space – Not a root /coal 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 • Modern basements are different – they need
different approaches! • Commercial basements are similar
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Basements – Part of the Enclosure
•
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Basements
• Below grade enclosure – Includes floor slabs, – practically need to include transition – Separates exterior (soil/air) and interior
• Functions of all parts of the enclosure – Support – heavy lateral loads – Control – less temperature, more water – Finish (usually)
www.BuildingScience.com Basements No. 5/73
Moisture: Old ideas
• CBD#161 - 1974 • Drainage layer • Exterior
moisture barrier • Exterior
insulation • Air barrier
Exterior insulation Drainage layer Capillary break Air tightness
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Control: Moisture
• Moisture causes most failures – Mold (musty basement 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? – 1. Exterior – 2. Built in – 3. Interior
Building Science Fundamentals–Basements
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1. Exterior Environment Moisture Sources
Solutions: Minimize Rain loads Provide Good Shedding Provide Good Drainage Provide 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.
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1. Controlling Exterior Moisture Sources
• Same approach as above-grade rain control – Deflection
• Overhangs, slopes, gutters – Drainage/Exclusion/Storage
• Three strategies for the enclosure – Drying
• Remove built-in incidental moisture
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www.BuildingScience.com Basements No. 9/73
Control Exterior surface water
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Surface Drainage
• First step – Common problem
• Overhang • Gutters • Downspouts • Sloped grade • Perimeter drain
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Solution
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Problem
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Exterior surface water • Drainage wont help here • Damage recovery
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Basement Enclosure Strategies
• Classification of Groundwater control – 1. Drained
• Needs capillary break and gap/drain space
– 2. Perfect Barrier (“waterproofing”) • One layer of perfect water resistance • Beware hydrostatic forces
– 3. Storage (mass) • Safe storage capacity and drying • Don’t use vapor barriers, do insulate (carefully)
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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
Drainage by specific backfill soil properties
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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
Drain can be gutter or new draintile www.BuildingScience.com
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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 can be used to reduce hydrostatic pressure • waterproofing layer resists significant head of water
Backfill – not necessarily free draining
No Drainage – hydrostatic pressure developed
Lowers water table, reduces hydrostatic pressure
Must use waterproofing below water table!
Slab? Connection?
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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 Waterproofing resists standing head of water
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Air gap membranes aka Dimple Sheets • provide drainage gap • act as vapor barrier
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Glassfiber Drainage Gap
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Rockwool Drainage Layer Can be insulation if thicker
Rockwool Drainage Gap
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•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.
2. Built-in Moisture
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2. Localized Flooding (abnormal - Water & Vapor)
2. Localized Flooding
1. Control interior vapor levels by: • winter ventilation • summer dehumidification
1. Avoid contact with cold surfaces • keep surfaces warm • stop water vapor moving
2. Control flooding • floor drains • disaster pans at appliances
2.
2.
3. Interior Moisture Sources
1. Water Vapor in contact with cold surfaces: air movement, and diffusion
Solutions
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Vapor failure– not ground water
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Managing Air and Vapor
• Need to solve – Surface condensation
• Sol’n: Keep surface warm & air dry
– Interstitial condensation • Control air/vapor flow to cold surfaces & dry air
– Solar driven summer condensation • Allow vapor flow in, slow rate of flow
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Context: Below-grade 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 grade • Significant vertical temperature gradients
– Top is different than bottom
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Typical Soil Temperatures
2.0 m
-5 0 5
10 15 20 25
Jan Feb Mar Apr May Jun Jul Aug Sept Oct Nov Dec Date
Tem
pera
ture
(C)
0.1 m 0.5 m 1.0 m 3 m
For 7500 F HDD climate
4” 20” 36” 110”
32
40
50
60
68
25
Note: open field values. No house to add heat
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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
Measured Soil / Air Temperatures
Daily Average temperatures – smooths air temperature, reduces peaks -15
-10
-5
0
5
10
15
20
25
30
2005/09/28 2005/10/28 2005/11/27 2005/12/27 2006/01/26 2006/02/25 2006/03/27 2006/04/26 2006/05/26 2006/06/25
Tem
pera
ture
(C)
Outdoor Air
36 in deep
12 in deep
6 in Deep
Tem
pera
ture
(F)
32
15
50
68
7500 F HDD Climate
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Exterior Temperature & Moisture Conditions
• Soil Relative Humidity almost always =100%
• Liquid water may be present
Temperature 20 0 10
Summer July
Winter Jan.
32 50 70
Above-grade design
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-10.0 -5.0 0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0
Temperature (°C)
0
500
1000
1500
2000
2500
3000
3500
4000
100% RH75% RH50% RH25% RH
Basement Psychrometrics
Summer
Winter
-10 ºC 14 º F
0 ºC 32 º F
10 ºC 50 º F
20 ºC 68 º F
30 ºC 86 º F
40 ºC 104º F
Since soil is at nearly 100%RH, the vapor drive is almost always inward except at very top (& rim) during winter in humid houses
Janu
ary
top
fo
otin
g
July
foot
ing
to
p
Flow out
Flow in
Flow in
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Basement Vapor Diffusion
• Water vapor is moving from soil to interior – for almost the entire year – over all but the top foot of basement
• Hence, should place vapor barrier on outside • But we put it on the inside!
• Moisture from drying concrete, air leakage, wicking and soil also trapped by interior vapor barriers
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Air & Vapor Wetting Sources
fo noisuffiDConstruction Moisture
Air Leakage of Interior / Exterior Air
Capillary Wicking of Soil Moisture
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Basement in a Bag – “The Diaper” • Tolerable north of Arctic Circle
No drying to the interior possible
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• Typical basement (“normal practice”)
1. Start dry 2. No leaks 3. No poly 4. Be lucky
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How to insulate/finish basement wall?
• We need to: – Control exterior ground water – Insulate (energy, comfort and moisture) – Control air leakage and diffusion condensation – Provide (a little) inward drying – Accommodate different conditions over height
• How to do we all this?
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Insulation Location Choices
• Builders like to insulate the interior
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Hybrid
• Add layer of: – foam or – spray
foam To allow inward drying • about 1 perm
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Retrofit
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Retrofit
Dimple sheet
• Repair – Wall leaks
groundwater • Retrofit/Reno
– Risk reduction • Min 1” XPS • Energy: 3”+EPS
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Drainage of peel and stick or dimple sheet provide superior drainage and leak resistance
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Retrofit Slab, drainage and sump before wall insulated
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Basement Wall Air Movement
• Water vapor moves along with airflow • If moist air touches a cold surface,
condensation occurs – Summer and winter problem
• Control? – Include an air barrier – Avoid air loops – Manage pressures
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Air leakage
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Internal Stack Effect & Insulation
Hot air = light
Cold air = heavy
• Gaps in batt insulation on both sides •Wrinkles inevitable
Air gaps Batt
Inside
Outside Common basement problem
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Internal Stack Effect Cold Weather
Hot air = light
Cold air = heavy
Result: Air Flow
• Gaps in batt insulation on both sides • closed circuit • energy cost • condensation
cold
cool
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Problems w/ air permeable insulation
Air leakage
Air permeable insulation
Crack
Cold
Condensation
Cold Weather
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Solution w/ Insulated Sheathing
Air leakage
Air permeable insulation
Crack
Warmer
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• Foam only • Vertical or
horizontal furring
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Basement Heat Loss
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Slab heat loss
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Spray foam basement insulation
• Open cell – Climate specific
• Closed cell
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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 6/inch – vapour semi-permeable (Icynene much more)
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Insulated Concrete Forms (ICF)
• If you afford it, use them – – cap break, – insulation, – vapor retarder, – above grade
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Thermomass www.BuildingScience.com
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Rim joists
• Scenario – Wood generally on exterior – 1.5” 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
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Slabs
• Slabs can loose significant energy – Currently the only uninsulated part of many
buildings • Keep warm (comfort & condensation) • Control wicking and diffusion • Make softer • Consider floods
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OSB over heavy poly dimple sheet vapor barrier and some insulation Air seal joints/edge
Beware Joints
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Slabs
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Summary
• Control surface water by drainage • Drainage layer on exterior of walls • No vapor barriers on inside • Painted drywall, stud, batt with foam OK • Care needed at rim joist • What happens if there is a flood, leak, etc.
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Conclusions
• Building in a hole in the ground is hard • Drainage is better than waterproofing • Don’t forget about built-in moisture
– and remember summer • Insulation and drainage are the best tools,
not vapor barriers and waterproofing
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Inward Solar Drives at Grade
• Wet concrete from rain, grade, built-in • Sun shines on wall and heats it • Water evaporates and diffuses in & out • Can condense inside if cold and
impermeable
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2.Vapour drives inward (& out)
3.Condensation on “cold” surfaces
1. Temperature and solar heating
warms wet lairetam
Wetting If impermeable
Drying If permeable
3.Vapour dries to inside
Inward Diffusion @ grade
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-10.0 -5.0 0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0
Temperature (°C)
0
500
1000
1500
2000
2500
3000
3500
4000
100% RH75% RH50% RH25% RH
Hot Wet materials
• 30-60 C • 90-100% RH •VERY high vapour pressure
Summer Winter
-10 ºC 14 º F
0 ºC 32 º F
10 ºC 50 º F
20 ºC 68 º F
30 ºC 86 º F
40 ºC 104º F
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