Basements are Changing. This presentation. University of Waterloo John Straube Presentation 1

Transcription

1 Building Better Basements, or How to Build Basements that Don t Stink Dr John Straube Assistant Professor Dupont Young Professor University of Waterloo BEG Building Engineering Group 2 /71 This presentation Basements are Changing Basements How are they changing What they do Performance Problems Causes Solutions 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! 3 /71 4 /71 John Straube Presentation 1

2 Basements Part of the Enclosure 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) 5 /71 6 /71 Functions of the building enclosure Support (Structural performance) Support Structural system Structure: wind, gravity, earthquake Does not work based on rational analysis 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) Don t ask for an engineers stamp Failure modes Poorly compacted subsoil Top-edge Bracing Raised bungalows Stairwells parallel to wall 7 /71 8 /71 John Straube Presentation 2

3 Basement Structural System Basement Structural System Similar for most basements Above Grade Raised Bungalows Stairs Foundation Wall Below Grade Above Grade Below Grade Floor slab Floor slab Footing Footing 9 /71 10 /71 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 11 /71 12 /71 John Straube Presentation 3

4 From: Lstiburek 2002 Exterior surface water Surface Drainage First step Common problem Overhang Eavestrough Downspouts Sloped grade Perimeter drain 13 /71 14 /71 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.) 15 /71 Exterior surface water Drainage wont help here Damage recovery 16 /71 Minimize by: Delay finishing internally Reduce water in concrete 1. & & 2. John Straube Presentation 4

5 Initial Drying Soil cold for first yr Excavation collects water Concrete is wet liters/m 2 Cannot dry to wet exterior Solutions = dry in No low perm interior Semi-permeable insulation Smart vapor barrier From: Lstiburek /71 18 /71 Basement in a Bag Tolerable north of Arctic Circle Moisture Sources: from Exterior Environment 1. Precipitation 2. Rainwater shedding 3. Surface water Run-off 4. Water vapor 5. Sub-surface Moisture - Groundwater - Vapor Minimize Rain loads Provide Good Shedding Provide Good Drainage Provide Capillary Breaks 19 /71 5. Sub-surface Moisture /71 A wet basement ground water John Straube Presentation 5

6 Controlling ground/rain water Many different acceptable methods Classification of Groundwater control 1. Drained Needs capillary break and gap/drain space 2. Perfect Barrier One layer of perfect water resistance Beware hydrostatic forces 3. Storage (mass) Exterior Moisture Safe storage capacity and drying Don t use vapor barriers, do insulate (carefully) Screened(1) Below-Grade Enclosure Wall System Drainage by specific backfill soil properties 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 Above Grade Level A. Screen (similar to cladding---shed and screen surface moisture-rain) B. Drainage crushed stone Below Grade Level B. Drainage draining backfill Interface with undisturbed below grade environment 21 /71 22 /71 1/31/2005 Collection and John Exit Straube Drain Screened(2) Below-Grade Enclosure Wall System Non-soil drainage layer 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 Above Grade Level A. Screen -optional (similar to cladding---shed and screen surface moisture-rain) Below Grade Level Backfill not necessarily free draining B. Drainage crushed stone Interface with undisturbed below-grade environment Screened(3) Below-Grade Enclosure Wall System Interior Drainage (often retrofit) 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 Above Grade Level Below Grade Level B. Backfill not necessarily free draining B. Drainage crushed stone A. Screen optional (similar to cladding---shed and screen liquid moisture-rain and groundwater) Interface with undisturbed below grade environment 23 /71 1/31/2005 Collection and John Removal Straube Drain 24 /71 1/31/2005 Collector and Removal John Straube Drain John Straube Presentation 6

7 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 needed to reduce hydrostatic pressure waterproofing layer resists mm head of water 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 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 25 /71 B. Drainage (opt) crushed stone Lowers water table, reduces Collector and 1/31/2005 hydrostatic pressure John Straube Removal Drain 26 /71 B. Drainage (opt) crushed stone 1/31/2005 Collector and Exit John Drain Straube 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 B. Drainage (opt) crushed stone A. Screen optional (similar to cladding---shed and screen surface moisture-rain) Interface with undisturbed below grade environment Damproofing Capillary break = drainage plane, but needs gap vapour barrier? NOT waterproofing 27 /71 1/31/2005 Collector and Removal John Straube Drain 28 /71 John Straube Presentation 7

8 Glassfiber Drainage Layer Rockwool Drainage Layer 29 /71 30 /71 R k l D i L Dimple Sheets Drainage gap act as vapor barrier So little water = maybe no capillary break needed Controlling ground/rain water 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) Exterior Moisture Safe storage capacity and drying Don t use vapor barriers, do insulate (carefully) Perimeter Drains 31 /71 32 /71 John Straube Presentation 8

9 Moisture Sources: Localized Flooding (Abnormal) Air and vapor from Interior 1. Water Vapor Control interior vapor levels by: winter ventilation summer dehumidcation Control flooding floor drains disaster pans at appliances Surface condensation Interstitial condensation Solar driven summer condensation Drying retarders 2. Localized Flooding (abnormal - Water & Vapor) Psychrometric Chart /71 34 /71 Special Exterior Conditions Moisture not ground water 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 35 /71 36 /71 John Straube Presentation 9

10 Measured Soil Temperatures 25 Measured Soil Temperatures m m m 3 m Temperature (C) m 5 Note: open field values. No house to add heat 0 Jan Feb Mar April May June July Aug Sept Oct Nov Dec 37 /71-5 Date 38 /71 Waterloo Measured Soil Temperatures Soil Temperatures at University of Waterloo Weather Station (1999) Exterior Temperature and Moisture Conditions soil temp (50 mm) soil temp (200 mm) Temperature (C) Winter Jan. Summer July Soil Relative Humidity almost always =100% Liquid water may be present /71-5 Time (weeks from January) 40 /71 Temperature 1/31/ John Straube John Straube Presentation 10

11 Psych Chart: Air Vapour Content vs Temperature Air Moisture Content = vapour pressure (Pa, in Hg), humidity ratio (g/kg, grains/pd) Temperature Saturation 100%RH 75%RH 50%RH 25%RH Vapour Pressure (Pa) 25% RH ºC ºC ºC ºC ºC ºC 41 /71 42 /71 14 º F 32 º 1/31/2005 F 50 º F Tem perat ure ( C) 68 º F John Straube 86 º F 104º F 100% RH 75% RH 50% RH 100%RH /71 Basement Vapour Movement Vapor moves by Diffusion & Air movement Diffusion Water vapor moves from more to less Common rule: place vapor retarding layers on moist (i.e. high vapor pressure) side to control vapor diffusion Air Leakage Vapor moves with air flow (high to low pressure) Stop air flow or flow from dry side 100% RH 75% RH 50% RH top footing Below Grade Basement Psychrometrics Since soil is at nearly 100%RH, the vapor drive is almost always inward except at very top during winter in humid houses January footing top July Flow in Flow out Flow in Winter Summer 25% RH ºC ºC ºC ºC ºC ºC 44 /71 14 º F 32 º 1/31/2005 F 50 º F Tem perat ure ( C) 68 º F John Straube 86 º F 104º F Vapour Pressure (Pa) John Straube Presentation 11

12 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 outside But we put it on the inside! Moisture moving by diffusion from drying concrete and soil is trapped by interior vapor barriers Air Moisture Content Air Moisture Content Temperature 45 /71 46 /71 Basement Air Movement Water vapor moves along with airflow If moist air touches a cold surface, condensation occurs Control? Include an air barrer Avoid air loops Avoid pressures Condensation: Cool air contains less vapor Cool air increase RH Heat air decrease RH 47 /71 48 /71 John Straube Presentation 12

13 Air leakage 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 49 /71 50 /71 Internal Stack Effect Air movement (Stack Effect) Gaps in batt insulation on both sides closed circuit energy cost cold surfaces Cold Weather Hot air = light Result: Air Flow Cold concrete = summer & winter Hot air = light Result: Air Flow Cold air = heavy Cold air = heavy 51 /71 52 /71 John Straube Presentation 13

14 Wall w/ only Batt Insulation Wall w/ Insulated Sheathing Winter Cold Condensation Air permeable insulation Warmer Air permeable insulation Air leakage Air leakage Crack Crack 53 /71 54 /71 Materials to use? ICFs 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) If you afford it, use them cap break, insulation, vapor retarder 55 /71 56 /71 John Straube Presentation 14

15 Sill gasket air seal Urethane foam airseal Site sloped away from building Better Add layer of: foam or spray foam Sealant airseal Gypsum wallboard Insulation & service distribution space 2x framing Keep bottom of drywall ¾" off of finished floor Install capillary break or ½" plastic wood spacer under bottom plate Continuous sealant joint over bond break Plastic baseboard pre-manufactured drainage layer (shown) or free draining material Damproofing Poly vapor barrier 57 /71 58 /71 Sill gasket air seal Urethane foam airseal Site sloped away from building Best? 1x2 horizontal strapping Gypsum wallboard Insulation & service distribution space Keep bottom of drywall ¾" off of finished floor pre-manufactured drainage layer (shown) or free draining material Foam only Vertical strapping Continuous sealant joint over bond break Plastic baseboard Damproofing Poly vapor barrier 59 /71 Draintile in crushed stone 1/31/2005 wrapped John in geotextile Straube 60 /71 John Straube Presentation 15

16 Solar Drives at Grade Inward grade Wet concrete from rain, grade, built-in Sun shines on wall and heats it Water evaporates and diffuses in & out Can condense inside of cold and impermeable 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 61 /71 62 /71 Hot Wet materials Rim joists 100% RH 75% RH 50% RH 25% RH C % RH VERY high vapour pressure Summer Winter ºC ºC ºC 20 ºC 30 ºC 40 ºC 63 /71 1/31/2005 Tem perat ure ( C) 14 º F John Straube 32 º F 50 º F 68 º F 86 º F 104º F Vapour Pressure (Pa) 64 /71 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 John Straube Presentation 16

17 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 65 /71 66 /71 Slabs Summary Tolerable Risky Be perfect..& lucky 67 /71 68 /71 John Straube Presentation 17

18 Sill gasket air seal Urethane foam airseal Site sloped away from building Summary good Summary-best best 1x2 horizontal strapping Gypsum wallboard Insulation & service distribution space Keep bottom of drywall ¾" off of finished floor pre-manufactured drainage layer (shown) or free draining material Continuous sealant joint over bond break Plastic baseboard Damproofing From: Lstiburek 2002 Poly vapor barrier 69 /71 70 /71 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 Conclusions Addition 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 Repair Wall leaks groundwater Retrofit/Reno Risk reduction publications 71 /71 72 /71 John Straube Presentation 18