Moisture and Buildings Joseph Lstiburek, Ph.D., P.Eng John Straube, Ph.D., P.Eng Building Science Moisture Moisture is involved in almost all building envelope performance problems In-service... Durability Examples: rot, corrosion, mould (IAQ) termites, (!), staining etc. presented by www.buildingscience.com No.2/78 Moisture Damage RH>80%, surface wet warmer= better Damage caused by Very high humidity for a long time Wet (100%RH) for a shorter time Time required depends on material Temperature Higher temperature accelerates process No.3/78 No.4/78
Near saturation combined with hard freeze No.5/78 No.6/78 Moisture Control RH>80%, surface wet warmer= better No.7/78 Moisture-related Problems 1. Moisture must be available 2. There must be a route or path 3. There must be a force to cause movement 4. The material must be susceptible to damage Theory: eliminate any one for complete control Practice: control as many as possible No.8/78
Moisture Balance Moisture Balance: Accumulation Wetting Wetting Wetting Wetting kg Safe Storage Capacity Drying kg Safe Storage Capacity! Drying No.9/78 No.10/78 Moisture Balance Wall + Roof Wetting Sources/ Mechanisms kg Safe Storage Capacity Wetting Wetting Drying Drainage Air convection Evaporation-Diffusion No.11/78 1. Rain absorption penetration splash and drips 2. Water Vapor Movement Diffusion Convection (air leaks) 3. Built in 4. Ground Capillary (wicking) Gravity Diffusion No.12/78 www.buildingscience.com 3
Wall + Roof Drying Sinks and Mechanisms 1. Surface Evaporation Wicking to surface 2. Vapor Movement i) Diffusion ii) Convection 3. Drainage 4. Intentional Convection = Ventilation Drying Note above and below grade Ventilation Drying Ventilation provides drying to the exterior Can be important for: 1. vapor impermeable cladding metal panels most roofing 2. systems which retain rainwater Improves survivability of small rain leaks and condensation Clear Air Spaces Vent Holes Above & Below Window Vent Holes at Top & Bottom of Wall Vented roofs soffit to ridge/gable No.13/78 No.14/78 Storage Bridges gap in time between wetting and drying How much moisture for how long before damage Safe storage: safe against what? mold, rot, freeze-thaw, corrosion Basic mechanisms Absorbed into materials= capillary pores (bound liquid) Adsorbed to materials = sorption (vapor) pools and puddles (free liquid) Moisture Storage in Assemblies 1. Trapped / undrained 2. Surface tension Liquid or solid 3. Adsorbed 4. Absorbed 5. Vapor small 3,4 No.15/78 No.16/78
Design Choices Either avoid wetting Or, provide enough drying to accommodate wetting Depending on the storage provided The balance has shifted over time Amount of storage has changed over last 100 yrs e.g. steel stud, vs wood stud vs concrete block 1: 10 : 100+ Wetting is usually less Drying is often much less Design Solutions Balance wetting, drying, and storage Practical Rules Provide a continuous plane of rain control including each enclosure detail Provide continuous air barriers and insulation to control condensation problems Allow drying of built-in and accidental moisture beware drying retarders No.17/78 No.18/78 The Water Molecule The Polar Molecule Asymmetrical = polar Small: one billion = one foot + Hydrogen end is more positive Oxygen end is more negative 0.28 n 3 Å H + + - Heat Air and Moisture No.19/78 O 2- H + O 2- H + H + _ + _ No.20/78
Water: Liquid vs Vapor Moisture as a Gas (water vapor) Vapor is a single molecule Liquid is molecular clumps, 60 or more Tyvek vs asphalt Vapor Liquid No.21/78 No.22/78 Psych Chart: Air Vapour Content vs Temperature Temperature 100%RH 4000 3500 Air Moisture Content = vapour pressure (Pa, in Hg), humidity ratio (g/kg, grains/pd) Saturation 75%RH 50%RH 25%RH 3000 2500 2000 1500 1000 100%RH 500 No.23/78 100% RH 75% RH 50% RH 25% RH -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 -10.0-5.0 0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0 Temperature ( C) No.24/78 0 40 ºC 104º F
Water vapor in Air Water vapor in Air 35 C 1 22 C 1 2 4 8 1 2 4 8 No.25/78 Building Science No.26/78 Water vapor in Air 35 C RH is relative 1 22 C 50%RH 50%RH 25%RH = = Building Science No.27/78 No.28/78
Condensation Methods to get Condensation 100%RH 50%RH 25%RH 1/2 = = = No.29/78 No.30/78 Definition of dewpoint 35 C Definition of dewpoint 35 C 1 22 C 50%RH 1 22 C 25%RH Building Science No.31/78 Building Science No.32/78
Indoor Conditions 68 78 F (20-26 C) 25 to 60%RH (Could be 20 to 70%) Dewpoint: 30-60F 4000 3500 3000 2500 Outdoor Conditions Summer / Winter January 35-50F / 0-1 &80-100% July 75-95F /24-35 C & 50-90% Dewpoint 60-85 F 4000 3500 3000 2500 2000 2000 Summer Winter 1500 1000 500 1500 1000 500 100% RH 75% RH 50% RH 25% RH -10 ºC 0 ºC 32 º F 10 ºC 50 º F 20 ºC 68 º F 30 ºC 86 º F -10.0-5.0 0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0 14 º F Temperature ( C) No.33/78 0 40 ºC 104º F 100% RH 75% RH 50% RH 25% RH -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 -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 40 ºC 104º F Warm weather condensation Dehumidification 1 22 C 35 C 1 50%RH 22 C 35 C 100% 75 % = = 75 % No.35/78 No.36/78
Cooling to get Condensation Cold weather condensation 100%RH 50%RH 25%RH 1 22 C 1/2 = = = No.37/78 Building Science No.38/78 Powerful means of controlling condensation in cold climate buildings Control interior RH 100%RH 1 21 C 70 F 50%RH 25%RH 12%RH Indoor vs Outdoor Conditions Inward drive bigger than outward Tighter control of T/RH increases drive Vapour Pressure Difference Summer 4000 3500 3000 2500 2000 1500 = = = Winter 1000 500 Building Science No.39/78 100% RH 75% RH 50% RH 25% RH -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 -10.0-5.0 0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0 Temperature ( C) No.40/78 0 40 ºC 104º F
Building Science No.41/78 No.42/78 Water Vapour Transport Vapour Diffusion Vapour Diffusion (like heat conduction) more to less vapour Air Convection (like heat convection) more to less air pressure flow through cracks and holes vapour is along for the ride Slow process through open pores Some materials allow easy diffusion Many, very open pores e.g. batt, gypsum, cellulose, etc. Many materials slow/retard diffusion small pored materials e.g., concrete, brick, stone Some stop, or practically stop it crystals, or micropore e.g., many plastics (poly), metals, glass No.43/78 No.44/78
No.45/78 No.46/78 Outdoor Conditions Summer / Winter January 35-50F / 0-1 &80-100% July 75-95F /24-35 C & 50-90% Dewpoint 60-85 F 4000 3500 3000 2500 Indoor vs Outdoor Conditions Inward drive bigger than outward Tighter control of T/RH increases drive 4000 3500 3000 2500 2000 1500 Vapour Pressure Difference Summer 2000 1500 1000 Winter 1000 500 500 100% RH 75% RH 50% RH 25% RH -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 -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 40 ºC 104º F 100% RH 75% RH 50% RH 25% RH -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 -10.0-5.0 0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0 Temperature ( C) No.48/78 0 40 ºC 104º F
No.49/78 No.50/78 Cold-weather air leakage condensation Air leakage pathways No.51/78 No.52/78
Building Science Water Vapor in Walls Enclosures No. 53 /