Air and Vapour Barriers - Who needs them, when, and where

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Air and Barriers - Who needs them, when, and where Dr John F. Straube Assistant Professor Dept of Civil Engineering & School of Architecture University of Waterloo Ontario, Canada www.civil.uwaterloo.

Vapor in air barriers Air Barriers Understanding Driving Forces Details of air barriers and airflow 1 2 Moisture Phases Wall Wetting Mechanisms As for most materials All four phases occur commonly in

1 Air and Barriers - Who needs them, when, and where Dr John F. Straube Assistant Professor Dept of Civil Engineering & School of Architecture University of Waterloo Ontario, Canada jfstraube@uwaterloo.ca Overview of Presentation Why? Vapor in air barriers Air Barriers Understanding Driving Forces Details of air barriers and airflow 1 2 Moisture Phases Wall Wetting Mechanisms As for most materials All four phases occur commonly in buildings AB and VB are interested in vapor form only evaporate 3 Liquid (water) condense thaw freeze frost Gas (water vapour, steam) adsorb desorb Solid (ice) sublimate Adsorbed 1. Rain Absorption splash and drips 2. Water i) Diffusion ii) Convection (air leaks) 3. Built in Moisture 4. Wicking (from ground) 4 Why use with AB or VB Water Pressure Code requirement Many codes requires VB Few require ABS! VB about controlling Moisture only helps control interstitial condensation AB about moisture condensation and comfort energy sound odour/smoke 5 6

Pressure For water vapour in a container Higher temperature = more energy higher velocity harder collisions with wall (higher pressure) Greater number of molecules = more collisions with walls

2 Pressure For water vapour in a container Higher temperature = more energy higher velocity harder collisions with wall (higher pressure) Greater number of molecules = more collisions with walls (higher pressure) pressure simply another measure for moisture content Surface must be cold Cold surface 7 8 Warm surface Condensation Water in Air Water vapour exists in all air Air has a maximum vapour holding capacity This capacity changes dramatically with temperature When the maximum holding capacity is exceeded, condensation occurs These facts are summarized by the psychrometric chart 9 10 Psych Chart: Air Content vstemperature Air Moisture Content = vapour pressure (Pa, in Hg), humidity ratio (g/kg, grains/pd) Temperature Saturation 100%RH 75%RH 50%RH 25%RH Pressure (Pa) 100%RH 100% RH 75% RH 50% RH 25% RH ºC ºC ºC ºC ºC ºC 14 º F 32 º F 50 º F Temperature 12( C) 68 º F 86 º F John Straube 104º 2001 F 500

3 Condensation: Cool air contains less vapor Condensation on Cold Surfaces Why? temp drops so RH rises to 100% molecules slow down and stick to surface Indoor Conditions C / F 25 to 60%RH (Could be 20 to 70%) Summer Pressure (Pa) Outdoor Conditions Burlington, VT January -10 C / 14 F & 80% July 20 C/ 68 F & 75% Pressure (Pa) Winter % RH 75% RH 50% RH 25% RH 25% RH ºC ºC ºC ºC ºC ºC ºC ºC ºC ºC ºC ºC 14 º F 32 º F 50 º F Temperature 15( C) 68 º F 86 º F John Straube 104º 2001 F 14 º F 32 º F 50 º F Temperature 16( C) 68 º F 86 º F John Straube 104º 2001 F 100% RH 75% RH 50% RH Indoor vs Outdoor Conditions Why use an AB or VB? Inward drive can be as big as outward Pressure Difference Summer Winter Pressure (Pa) Code requirement NBCC -> OBC requires AB/VB if damage can occur VB only required sometime, AB almost all times VB only helps control interstitial condensation AB about interstitial condensationand comfort energy sound odour/smoke 100% RH 75% RH 50% RH 25% RH ºC ºC ºC ºC ºC ºC 14 º F 32 º F 50 º F Temperature 17( C) 68 º F 86 º F John Straube 104º 2001 F 18

storage Masonry Little to some vapour resistance Little moisture storage Little insulation / air leaky = dry! No vapour barrier of course No vapour barrier of course t Plaster 21 22 Changes.

4 Diffusion and Convection Water vapour moves by 1. vapour diffusion more to less vapour 2. air convection more to less air pressure vapour is along for the ride Find the vapour barrier In the beginning Old Assemblies Old Framed Assemblies Integral vapour resistance Massive moisture storage Masonry Little to some vapour resistance Little moisture storage Little insulation / air leaky = dry! No vapour barrier of course No vapour barrier of course t Plaster Changes... Dr Frank Rowley Increase in wood frame, esp. post WW1 Began to add insulation comfort wood scarcity, coal Moisture problems in cold climates noted in 1930 s Paint peeling of siding t Professor of Mechanical Engineering at University of Minnesota ASH&VE 1932 president Proponent of using heat flow analogy for vapor flow in calculations Conducted full scale house in climate chamber studies paid for by insulation companies 23 24

5 The One US Perm The Sales Job This Test research house inside resulted climate in 1 chamber perm / 60 ng/pa s m 2 or less vapor barriers 21 C/ 70 F 40% RH -29 C/-20 F No VB: 21.5 g/m 2 /day (0.07 ounce/ft 2 /day) ASH&VE Transactions No 44, Condensation Within Walls 25 Paint manufacturers Stop peeling due to insulation aluminum foil manufacturers Open up a new market On the recent aluminum foil for cooking: in a period of less than 12 months, through national advertising, through local advertising and through point of purchase advertising, a product was created that it will take a lot of promotional work to kill Barriers barriers in Code: <1 US perm 1942 first reference Canadian codes as of 1975 retarder approx 2-5 US perm Measurement Units Metric perms ng /(s m 2 Pa) US perm grain/(hr in Hg ft 2 ) WVT grams/(sq ft/24 hours) Air barriers discovered Air leakage identified by Neal Hutcheon, 1950: The rate of condensation is about ten times that at which vapour might be expected to diffuse through It seems necessary to assume some other mechanism the leakage of warm moist air outward.. Solution suggested by many: Why not use the vapour barrier Add sealed or continuous to codes language Air barriers spelled out in 1985 NBCC Why poly? When and where Poly is cheap and easy Cliff Shirtcliff Insulation shortage Paper-facings hide insulation Choice of vapour permeance and location of vapor barrier depends on Exterior Climate Interior Climate Wall Assembly Any rule that does not consider these factors cannot provide correct guidance 29 30

6 Some rules: When and Where Old rule: Place on warm side of enclosure summer and winter balance If you use a VB on cold side of wall - ventilate! If extreme temps/rh use VB (beware air leakage) Use lower perm insulation (foam) If moderate, use retarder, like paint Insulated sheathing changes everything If in doubt - figure it out 31 Severe Cold Cold Mixed-Humid Hot-Dry Joe Lstiburek s Builders Guides 32 Climate and VB Florida is hot and humid moisture is outdoors place VB near outside allow vapour to flow INWARD Winnipeg/Bismark is cold/dry bitterly cold winters summers are hot and dry place VB near inside allow vapour to flow outward Climate and VB Vancouver/Seattle moisture is both indoors outdoors allow vapour to flow inward and outward use VR near inside (paint) Toronto/Detroit summers are hot and humid, winters cold if rain-wetted cladding, inward is important! allow vapour to flow inward and outward use VR near inside (paint) or exterior insulation VB and Wall design Water Diffusion Need vapour barriers low integral vapour resistance framed walls with batt Rarely need VB: Integral vapour resistance SIPS spray foam Built in VB concrete Kept warm insulating sheathing 35 More Warm humid weather Less Condensation Diffusion Cold Surface 36 Cold weather More

Diffusion Movement from more vapour to less Slow process Many materials slow this process concrete, brick, stone Some stop, or pratically stop

stone Some materials stop, or practically stop it many plastics (poly), steel, glass Some materials resist very little Housewraps, batt,

sensitive to air leakage 32 F 50 F 39 68 F 40 4000 Air Leakage vs Diffusion Air Leakage Condensation 100%RH 75%RH 50%RH Summer 25%RH 3500 3000

7 Diffusion Movement from more vapour to less Slow process Many materials slow this process concrete, brick, stone Some stop, or pratically stop it many plastics (poly), steel, glass Diffusion Movement from more vapour to less Slow process Many materials slow this process concrete, brick, stone Some materials stop, or practically stop it many plastics (poly), steel, glass Some materials resist very little Housewraps, batt, fibreboard Air leakage vs Diffusion Air leakage is much more critical Walls sensitive to diffusionrelated condensation will be more sensitive to air leakage 32 F 50 F F Air Leakage vs Diffusion Air Leakage Condensation 100%RH 75%RH 50%RH Summer 25%RH Pressure (Pa) Winter % RH 75% RH 50% RH 25% RH Diffusion Temperature 42( C) 0

Solution to Interstitial Condensation Wall with Insulated Sheathing Air leakage install air barriers and insulated sheathing Vapor diffusion choose materials, insulated sheathing, and/or install

8 Solution to Interstitial Condensation Wall with Insulated Sheathing Air leakage install air barriers and insulated sheathing Vapor diffusion choose materials, insulated sheathing, and/or install vapor barrier Sheathing Air Permeable Insulation Warm = No Condensation Diffusion VB and Wall design Calculations Need vapour barriers low integral vapour resistance framed walls with batt Rarely need VB: Integral vapour resistance SIPS spray foam Built in VB concrete Kept warm insulating sheathing 45 Simple calculations can used to understand the issue Computer models are useful for complex situations 46 Barriers barriers in Code: <1 US perm based on Rowley 1937 no good science retarder approx 2-5 US perm Measurement Units Metric perms ng /(s m 2 Pa) US perm grain/(hr in Hg ft 2 ) WVT grams/(sq ft/24 hours) Low-perm Materials 6 mil Poly 0.1 US perm Vinyl wall paper 0.3 perm Concrete 1/2 perm for 8 foundation wall Drywall with a VB paint 0.1 to 1 perm Brick veneer 1/2-2 perms Extruded foam 1/2-1 for 1.5 Plywood 0.5 to 20 (dry to wet) Kraft paper 0.3 to 2 (dry and wet) 47 48

Mid-perm Materials High-perm Materials Plywood 0.5 to 20 (dry to wet) Fibreboard over 20 Expanded foam 2.5-5 perms for 1 inch Plywood 0.

9 Mid-perm Materials High-perm Materials Plywood 0.5 to 20 (dry to wet) Fibreboard over 20 Expanded foam perms for 1 inch Plywood 0.5 to 20 (dry to wet) Spray PUR about 2 perms Icynene open cell spray foam Drywall with latex paint (2-5 perms) Tyvek other housewraps 20 to 50 perms Building paper over 10 to Permeance: Sheathing When and Where Permeance (ng/pa s m2) Dry Cup 11.1 mm OSB 12.7 mm Plywood Wet Cup Place on warm side of enclosure summer and winter balance If you use a VB on cold side of wall - ventilate! If extreme temps/rh, use VB If moderate, use VR If in doubt - figure it out Climate is one simple rule Relative Humidity Climate and VB Severe Cold Cold Mixed-Humid Hot-Dry Florida is hot and humid moisture is outdoors place VB near outside allow vapour to flow INWARD Winnipeg/Bismark is cold/dry bitterly cold winters summers are hot and dry place VB near inside allow vapour to flow outward Joe Lstiburek s Builders Guides 53 54

10 Climate and VB VB and Wall design Vancouver/Seattle moisture is both indoors outdoors allow vapour to flow inward and outward use VR near inside (paint) Toronto/Detroit summers are hot and humid, winters cold if rain-wetted cladding, inward is important! allow vapour to flow inward and outward use VR near inside (paint) or exterior insulation 55 Need vapour barriers low integral vapour resistance framed walls with batt Rarely need VB: Integral vapour resistance SIPS spray foam Built in VB concrete Kept warm insulating sheathing 56 Wall w/o Insulated Sheathing Wall with Insulated Sheathing Sheathing Air Permeable Insulation Sheathing Air Permeable Insulation Cold = Condensation Diffusion Warm = No Condensation Diffusion Drying barriers stop wetting and drying Overkill (e.g. poly) can cause problems! Inward drying is useful in many climates Vapor flows in both directions diffuses from more to less Hence, indoors to outdoors in cold weather Outdoors to indoors in hot humid weather From wet materials to in and outdoors Locating low permeance materials within assemblies must respect these facts 59 60

Inward Drives Inward Diffusion Long understood by researchers When a vapour barrier is used, the wall can loose moisture only to the outside.

Hutcheon 1953 Most published work from cold climates Canada, Sweden, Denmark, Belgium, Germany Rarely considered by practioners If you don t know, you don t see it 1.

Condensation on cold surfaces 61 62 Indoor Conditions 4000 3500 18-26 C / 65 78 F 25 to 60%RH (Could be 20 to 70%) Summer Winter 3000 2500 2000 1500 1000 500 Pressure (Pa) 100% RH 75% RH 50% RH 25%

11 Inward Drives Inward Diffusion Long understood by researchers When a vapour barrier is used, the wall can loose moisture only to the outside. In summer, hot sun following a rain drives moisture as vapour to the inside of the wall, and condensation behind the vapour barrier can occur. Hutcheon 1953 Most published work from cold climates Canada, Sweden, Denmark, Belgium, Germany Rarely considered by practioners If you don t know, you don t see it 1. Temperature and solar heating warms wet material 2. drives inward Drying If permeable 3. dries to inside Wetting If impermeable 3.Condensation on cold surfaces Indoor Conditions C / F 25 to 60%RH (Could be 20 to 70%) Summer Winter Pressure (Pa) 100% RH 75% RH 50% RH 25% RH ºC ºC 10 ºC 20 ºC 30 ºC 40 ºC Temperature 63( C) 14 º F 32 º F 50 º F 68 º F 86 º F John Straube 104º 2001 F 64 Control Strategies Low-perm vapor barriers limited interior drying, warm weather condensation Storage systems safely store moisture in absorbent materials, e.g. masonry Highly permeable walls high flow in, high flow out Insulated sheathing shift condensation to exterior, ventilate away Integral heat and vapor resistance e.g., many foams and natural insulating materials 65 66

12 Air movement Channel Movement of air (and its heat, moisture, pollutants) from high air pressure to low Delivers vapour directly to cold surface Air movement causes other problems Diffuse Tortuous Glass is a perfect VB 71 72

13 Airflow Control: What Air flow through enclosure Air flow within enclosure Design Goal: Eliminate air flow Air Flow is driven by Air Pressure Differences Airflow Control: Why Condensation wetting Drafts (= comfort) Energy Pollutant transport - smell, particles, gas Sound NOT just energy!! Airflow Control: Where Stop airflow = stop most problems Can locate anywhere in enclosure should be protected if possible multiple layers are good important in all climates Air Leakage Difficult to predict direction of air pressures and unintentional flow paths Damaging airflow direction is: cold weather inside to outside warm weather outside to inside Condensation can ONLY occur if both: air contacts a cold surface, and air flow is in the direction of more to less vapour Many materials stop airflow, most systems do not More Pressure Air leakage (Convection) Warm Weather Less Pressure Condensation if more vapour Diffusion Cold Surface 77 Cold Weather More Pressure Air Barrier Systems Air barrier systems are required to stop airflow through enclosure ABS can be placed anywhere in the enclosure Must be strong enough to take wind gusts Air barrier systems must be continuous They leak at joints, interfaces, penetrations multiple air barrier planes are useful for redundancy 78

Air Barrier Systems Continuous primary need Strong designed for full

Paper is not an air barrier Stiff control billowing, pumping Air

Condensation Stop all airflow Control driving forces (HVAC/ air

moisture load (only useful for cold weather) 1.

14 Air Barrier Systems Continuous primary need Strong designed for full wind load Durable critical component - repair, replacement Stapled Paper is not an air barrier Stiff control billowing, pumping Air Impermeable (may be vapour permeable) Control Air Leakage Condensation Stop all airflow Control driving forces (HVAC/ air pressures) Control Temperature of condensing surface Reduce interior moisture load (only useful for cold weather) 1. Stop Leaks Find the holes and plug them This requires finicky attention to 3-D details Typical Air Leakage Points 83 84

15 Air sealing around windows and other openings A small hole in the air barrier Poly can be (?) an air and vapour barrier Beware: poly is a VB -- keep on warm side 90

Joe Lstiburek Builders Guide 91 92 ADA Detail Window From NRCan Super-E 93 94 ADA Detail

16 The Airtight Drywall Approach Use drywall, framing members Seal with sealant, gaskets, etc. Is stiff, strong Often easier to get better Drawing From: Dr. Joe Lstiburek Builders Guide ADA Detail Window From NRCan Super-E ADA Detail Rim Joist 2. Control Temperatures A potent cold-climate strategy for framed enclosure systems 95 From NRCan Super-E 96

17 Insulated Sheathing Wall w/o Insulated Sheathing Increases temperature of first condensation surface in winter adding R5 to R7 on exterior of R12 batt practically eliminates possibility of condensation Many foam sheathings reduce summer vapour drives, e.g., they have permeances of M<200 Some sheathings are vapour impermeable -- they reduce drying outward! Remember Insulated Sheathing = Moisture Control Strategy 97 Cold = Condensation 98 Air leakage Diffusion Wall with Insulated Sheathing Warm = no condensation Air leakage Diffusion 3. Control Driving Pressures Wind+stack: understand them. Control HVAC pressures! Control stack by compartmentalization Reduce interior vapor content Driving Forces Wind Major driving force Codes - Extensive data for Structural Design Loads Average pressures much lower Wind Pressure Increases with Height Exposure Conditions Matter! Beware Corner and Suction pressures Wind Effect Stack Effect Combustion and Ventilation

18 30% 25% Wind Speed Distribution Avg. 3.6 m/s = 8 mph Windspeed Varies with Height and Exposure Relative Frequency 20% 15% 10% 5% 1/10 yr cladding: 1 sec/10 yr 1/30 yr structure: 3 sec/ 30 yr For Waterloo, Canada 0% Wind 103 Speed (m/s) 104 Wind speed to Pressure Flow Patterns Wind Velocity to Pressure: P stag = 0.647? V 2 [in Pa and m/s] Lowrise 10 m= 4 m/s Highrise 50 m=8 m/s 10 Pa 40 Pa Velocity 105 Stagnation Pressure 106 Pressure Distribution on Face Wind Pressures / Flow Patterns Pressure on windward side Suction on lee and sidewalls + Peak Suctions at Sides

Plane at mid-height + Cold weather example Pressures at a specific height Stack Effect Pressures NPP 111 112

19 Wind Pressure Distribution Stack Effect Hot air rises Tall Building in Winter = Heavy Balloon Plan View +? P Stack Effect Stack Pressure Distribution Perfect Building equally leaky everywhere Neutral Pressure Plane at mid-height + Cold weather example Pressures at a specific height Stack Effect Pressures NPP Wind Stack Rain Pressurization More airflow forced into building than sucked out of building = Pressurization + Fan

20 De-Pressurization Pressure Distribution More airflow forced out of building than forced into building = De-Pressurization Combined Pressures Stack Pressure + HVAC Pressures Wind Pressures Fan Control HVAC Effects Can be reduced by controlling fan operation In many houses, exhaust-only fans depressurize less air leaks outward good for cold weather Commercial buildings often pressureize to reduce drafts don t do this in cold weather -- plug holes! Airflow Within Enclosures Pressure Distribution Pressure Distribution Plan View Plan View? P? P

21 Lateral Airflows Internal Stack Effect & Insulation Condensation inside (cold) Condensation backside (hot) Punched Steel Studs Gaps in batt insulation on both sides Stapled paper! Inside Batt Hot air = light Air gaps 121 Cold air = heavy Outside Common performance problem 122 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 Weather Hot air = light Result: Air Flow Cold air = heavy Cold air = heavy More Air movement (Stack Effect) Warm Weather Condensation if more vapour Air Flow Cold Surface 125 Cold Weather More Airflow within enclosures Provide lateral airflow resistance as required allow easy lateral flow batt insulation open cell foam slow lateral flow very high-density fibrous insulation dense packed cellulose stop lateral flow closed cell foam solid materials 126

Windwashing Control lateral flow Need some

housewrap, attached building paper Sheathing

high density MI High density cavity insulation

128 Suction on sides Using Exterior Sheathing as

22 Windwashing Control lateral flow Need some airtightness outside permeable insulation Sealed housewrap, attached building paper Sheathing sealed with tape both OSB and insulated sheathing high density MI High density cavity insulation some foams, maybe dense cellulose Pressure Profile Airflow behind cladding causes cooling or "wind washing" of air permeable insulations Suction on sides Pressure Profile Framing members and compartment seperators control air flow Suction on sides Using Exterior Sheathing as air Barrier Not Not How long will the tape last? HVAC Interaction

23 HVAC: The Way it is Designed HVAC : The Way it Works Air Handler Perfect ducts Air Handler 20 cfm leakage + + Warm Moist Air 100 cfm 100 cfm The Air+ Thermal Barrier Warm 20 cfm Moist Air 100 cfm The Air+ Thermal Barrier 80 cfm More Pressure Warm Humid Depressurization = Air leakage Warm Climate Condensation if more vapour Less Pressure Cool HVAC Solutions Hot-humid climates pressurize with conditioned outdoor air Cold climates depressurize by exhausting air properly sized transfer grilles (small? P) keep ducts inside! (or seal ducts) Good air barrier systems for the enclosure Cold Surface Internal Moisture Loads Critically important for cold climate!! Primary load for vapour diffusion and air leakage condensation More unknown (!) than exterior Temperature 8 to 76 F (21 to 26 ) Relative Humidity 20 to 75%? 137 Air Mositure Content = Pressure Air Content vs Temperature Reduce moisture loads = reduced condensation Air Leakage Condensation Saturation 80%RH 60%RH Temperature 138 (F) Summer Winter

24 Control Interior RH! Cold Climate Air-to-Air Heat exchanger Exhaust ventilation Interior Air Moisture Ventilation and Diffusion Remove Moisture 100%RH Outdoor Air Plus Moisture Production 20-60%RH Moisture Removal (ventilation, leakage, diffusion?) Sources of Moisture Within Buildings Source Strength kg per day People - evaporation per person 0.9 to 1.25 * Humidifier Hot tub, Whirlpool Firewood, per cord 1-3 Washing floors, counters, etc. 0.2 Dishwashing 0.5* Cooking for four 0.9 to 2 (3 with gas range)* Defrosting (frost free) Fridge 0.5* Typical bathing/washing per person 0.2 to 0.4* Shower (ea) 0.5 Bath (ea) 0.1+ Uncovered Crawlspace 0.5 / m 2 Unvented Gas Appliance (ea) 1 Seasonal Desorption 3-8 depends on the type of construction Plants/Pets (five small plants or one dog) Total (Typical Family of 4) About 10, but potential ranges 3 to Internal Moisture Total for Family of 4: 10 to 14 kg/day CMHC Study Of Detached Homes 90%> 3 kg/day and <21 kg/day Also drying out of rain wetting 142 Indoor RH For Outdoor Conditions of +5 C/80%RH 100% 80% 60% 40% 20% 0.1 ACH For 775 sf Apartment Moisture Production Rate (kg/day) 0% Air Changes per Hour Mechanical Ventilation Old houses had 3 or more ACH hence, moisture production rate had little effect on interior humidity New houses have 0.25 to 1 ACH hence, moisture production dominates interior humidity Mechanical ventilation ensures proper fresh air supply reduces energy consumption controls interior humidty 144

25 Interior Moisture Hot or Humid climates must remove interior moisture by dehumidification / A.C. Must size AC for latent load Must still provide guaranteed fresh air Airtight controls amount of exterior moisture brought in Wetting and Drying Air leakage and Diffusion can cause Wetting AND Drying Depends on Weather Conditions! barriers and air barriers reduce or slow flow in BOTH directions all vapour barriers slow inward drying all vapour resistant claddings and sheathings slow outward drying Conclusions Review Air Barrier Systems Air barriers and vapour barriers are different can be combined in same materials barriers control diffusion use only when needed place near WARM side only Air barriers control air flow can be placed any where Air barriers usually more important continuity is key! 147 Continuous primary need Strong designed for full wind load Durable critical component - repair, replacement Stiff control billowing, pumping Air Impermeable (may be vapour permeable) 148 Review Air Barrier or Barrier? When? Tyvek Concrete wall Steel roof Poly Drywall Peel and stick membrane Blue Extruded Styrofoam Review Where to place the VB in Miami Minnespolis Where to place the ABS Miami Minneapolis

Air Barriers & Vapour Barriers. Water Vapour Pressure. The 4 phases of Water. Water Vapour in Air. Water Vapour Pressure

Air Barriers & Vapour Barriers. Water Vapour Pressure. The 4 phases of Water. Water Vapour in Air. Water Vapour Pressure Building Science Air & Barriers Air Barriers & Barriers Air Barriers Control Air Leakage Heat (for comfort & energy considerations) Smoke & odours Sound Moisture Barriers Control Diffusion Moisture The