John Straube, Ph.D., P.Eng Basements: New & Retrofit Energy Efficient, Durable, Healthy Building Science Corporation presented by www.buildingscience.com
This presentation Basement functions Basement Performance Problems Causes Solutions Crawlspaces & Slabs next session 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 Basements No. 3/73
Basements Part of the Enclosure Basements No. 4/73
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 Control Finish (usually) Basements No. 5/73
Building Enclosure Functions 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 optional Distribute (sometimes) Basements No. 6/73
Moisture: Old ideas CBD#161-1974 Drainage layer Moisture barrier Exterior insulation Air barrier Exterior insulation Drainage layer Capillary break Air tightness Basements No. 7/73
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 Basements No. 8/73
1. Exterior Environment Moisture Sources 1. Precipitation 2. Rainwater shedding 3. Surface water Run-off 4. Water vapor 5. Sub-surface Moisture - Groundwater - Vapor Solutions: Minimize Rain loads Provide Good Shedding Provide Good Drainage Provide Capillary Breaks 5. Sub-surface Moisture 5. Basements No. 9/73
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 Basements No. 10/73
Control Exterior surface water Basements No. 11/73
Surface Drainage First step Common problem Overhang Gutters Downspouts Sloped grade Perimeter drain Basements No. 12/73
Solution Basements No. 13/73
Problem Basements No. 14/73
Exterior surface water Drainage wont help here Damage recovery Basements No. 15/73
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) Basements No. 16/73
Basement Ground Water Control Basements No. 17/73
Screened(1) Below-Grade Enclosure Wall System Drained type: drainage system with drainage plane, and capillary break Above Grade Level A. Screen (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 Below Grade Level B. Drainage draining backfill Drainage by specific backfill soil properties Interface with undisturbed below grade environment B. Drainage crushed stone Collection and Exit Drain Basements No. 18/73
Screened(2) Below-Grade Enclosure Wall System Drained type: drainage system with drainage layer& plane, capillary break Above 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 Below Grade Level Backfill not necessarily free draining Non-soil drainage layer Interface with undisturbed below-grade environment B. Drainage crushed stone Collection and Removal Drain Basements No. 19/73
Screened(3) Below-Grade Enclosure Wall System Interior Drainage (often retrofit) Drained type: drainage system with drainage plane, and capillary break Above 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 Below Grade Level B. Backfill not necessarily free draining Interface with undisturbed below grade environment B. Drainage crushed stone Drain can be gutter or new draintile Collector and Removal Drain Basements No. 20/73
Barrier (1) Below-Grade Enclosure Wall System No Drainage hydrostatic pressure developed 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 Above Grade Level Below Grade Level Backfill not necessarily free draining B. Drainage (opt) crushed stone Collector and Removal Drain A. Screen optional (similar to cladding---shed and screen surface moisture-rain) Interface with undisturbed below grade environment Must use waterproofing below water table! Slab? Connection? Lowers water table, reduces hydrostatic pressure Basements No. 21/73
Barrier (2) Below-Grade Enclosure Wall System No Drainage hydrostatic pressure developed 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 Above Grade Level Below Grade Level Backfill not necessarily free draining A. Screen optional (similar to cladding---shed and screen surface moisture-rain) Interface with undisturbed below grade environment B. Drainage (opt) crushed stone Collector and Exit Drain Basements No. 22/73
Storage (1) Below-Grade Enclosure Wall System Limited ability to resist moisture loads 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 Above Grade Level Below Grade Level Backfill not necessarily free draining A. Screen optional (similar to cladding---shed and screen surface moisture-rain) Interface with undisturbed below grade environment B. Drainage (opt) crushed stone Collector and Removal Drain Basements No. 23/73
Damproofing Capillary break = drainage plane, but needs gap vapour barrier? NOT waterproofing Waterproofing resists standing head of water Basements No. 24/73
Air gap membranes aka Dimple Sheets provide drainage gap act as vapor barrier Basements No. 25/73
Glassfiber Drainage Gap Basements No. 26/73
Rockwool Drainage Gap Rockwool Drainage Layer Basements No. 27/73
Controlling ground/rain water Review: Exterior Moisture Deflection: Roof and Surface Drainage Classification of Groundwater control 1. Drained Needs capillary break & gap/drain space 2. Perfect Barrier 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) Drying to Inside and Perimeter Drains Basements No. 28/73
2. Built-in Moisture 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 Reduce water in concrete 1. & 2. 1. & 2. Basements No. 29/73
Initial Drying Soil cold for first yr Excavation collects water Concrete is wet! to 1 gal/ft 2 25-50 liters/m 2 Cannot dry to wet exterior Solutions = dry in No low perm interior Semi-permeable insulation Smart vapor barrier From: Lstiburek 2002 Basements No. 30/73
3. Interior Moisture Sources 2. Localized Flooding 2. Solutions 1. Water Vapor in contact with cold surfaces: air movement, and diffusion 2. Localized Flooding (abnormal - Water & Vapor) 2. 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 Basements No. 31/73
Vapor failure not ground water Basements No. 32/73
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 Basements No. 33/73
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 Basements No. 34/73
Typical Soil Temperatures 25 For 7500 F HDD climate 68 20 0.1 4 m 0.5 20 m 60 Temperature (C) 15 50 10 40 32 5 0 2.0 m 1.0 36 m 3110 m Note: open field values. No house to add heat Jan Feb Mar Apr May Jun Jul Aug Sept Oct Nov Dec 25-5 Date Basements No. 35/73
Soil Temperatures 5 10 15 20 25 Basements No. 36/73
68 Waterloo Measured Soil 30 Temperatures 25 30 20 25 Waterloo Measured Soil / Air Temperatures Soil Temperatures at University of Waterloo Weather Station (1999) Outdoor Air 7500 F HDD Climate 36 in deep 12 in deep soil temp (50 mm) 6 in Deep soil temp (200 mm) 15 Temperature (F) 50 32 Temperature (C) 10 Temperature (C) 5 20 15 10 0 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 5-5 15-10 0 0 4 8 12 16 20 24 28 32 36 40 44 48 52-5 -15 Time (weeks from January) Daily Average temperatures smooths air temperature, reduces peaks Basements No. 37/73
Exterior Temperature & Moisture Conditions Above-grade design Soil Relative Humidity almost always =100% Liquid water may be present Summer July Winter Jan. 0 10 20 32 50 70 Temperature Basements No. 38/73
Basement Psychrometrics Since soil is at nearly 100%RH, the vapor drive is almost always inward except at very top (& rim) during winter in humid houses 4000 3500 3000 top footing January footing top July Flow in Flow out Flow in Winter Summer 2500 2000 1500 1000 500 100% RH 75% RH 50% RH 25% RH -10 ºC 14 º F 0 ºC 32 º F -10.0-5.0 0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0 10 ºC 50 º F Temperature ( C) 20 ºC 68 º F 30 ºC 86 º F 0 40 ºC 104º F Basements No. 39/73
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 Basements No. 40/73
Air & Vapor Wetting Sources Problems with fibrous insulation & vapor barrier Diffusion of Construction Moisture Air Leakage of Interior / Exterior Air Capillary Wicking of Soil Moisture Basements No. 41/73
No drying to the interior possible Basement in a Bag The Diaper Tolerable north of Arctic Circle Basements No. 42/73
Typical basement ( normal practice ) 1. Start dry 2. No leaks 3. No poly 4. Be lucky Basements No. 43/73
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 Basements No. 44/73
Air leakage Basements No. 45/73
Internal Stack Effect & Insulation Gaps in batt insulation on both sides Wrinkles inevitable Inside Hot air = light Batt Air gaps Outside Common basement problem Cold air = heavy Basements No. 46/73
Internal Stack Effect Gaps in batt insulation on both sides closed circuit energy cost condensation cold cool Cold Weather Hot air = light Cold air = heavy Result: Air Flow Basements No. 47/73
Problems w/ air permeable insulation Cold Weather Cold Condensation Air permeable insulation Air leakage Crack Basements No. 48/73
Solution w/ Insulated Sheathing Warmer Air permeable insulation Air leakage Crack Basements No. 49/73
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? Basements No. 50/73
Insulation Location Choices Builders like to insulate the interior Basements No. 51/73
Basements No. 52/73
Hybrid Add layer of: foam or spray foam To allow inward drying about 1 perm Basements No. 53/73
Basements No. 54/73
Best? No summer thermal lag Sub-slab insulation a plus Free Draining backfill or drainage membrane Basements No. 55/73
Foam only Vertical or horizontal furring Basements No. 56/73
Spray foam basement insulation Open cell Climate specific Closed cell Basements No. 57/73
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) Basements No. 58/73
Insulated Concrete Forms (ICF) If you afford it, use them cap break, insulation, vapor retarder, above grade Basements No. 59/73
Basements No. 60/73
Basements No. 61/73
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 Basements No. 62/73
Inward Diffusion @ grade 1. Temperature and solar heating warms wet material 2.Vapour drives inward (& out) Drying If permeable 3.Vapour dries to inside Wetting If impermeable 3.Condensation on cold surfaces Basements No. 63/73
Hot Wet materials 4000 3500 30-60 C 90-100% RH VERY high vapour pressure 3000 2500 2000 Summer Winter 1500 1000 500 100% RH 75% RH 50% RH 25% RH -10 ºC 14 º F 0 ºC 32 º F 10 ºC 50 º F -10.0-5.0 0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0 Temperature ( C) 20 ºC 68 º F 30 ºC 86 º F 0 40 ºC 104º F Basements No. 64/73
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 Basements No. 65/73
Basement New or retrofit Solves slab wetness & cold Basements No. 66/73
Slabs Keep warm (comfort & condensation) Control wicking and diffusion Make softer Consider floods Basements No. 67/73
OSB over heavy poly dimple sheet vapor barrier and some insulation Air seal joints/edge Beware Joints Basements No. 68/73
Slabs Basements No. 69/73
Retrofit Slab, drainage and sump before wall insulated Basements No. 70/73
Retrofit Drainage of peel and stick or dimple sheet provide superior drainage and leak resistance Repair Wall leaks groundwater Retrofit/Reno Risk reduction Min 1 XPS Energy: 3 +EPS Dimple sheet Basements No. 71/73
Summary Control surface water by drainage Drainage layer on exterior of walls Poly interior stop drying and often result in problems Painted stud with foam OK Care needed at rim joist What happens if there is a flood, leak, etc. Basements No. 72/73
Conclusions Building in a hole in the ground is hard Don t forget about built-in moisture and remember summer Moisture comes in liquid AND vapor Insulation and drainage are the best tools, not vapor barriers and waterproofing Basements No. 73/73