Air and Vapour Barriers - Overview of Presentation Who ... Comfort Air Vapour barri… · • Use lower perm insulation (foam)?If moderate, use retarder, like paint?Insulated sheathing

© John Straube 20011

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

Dr John F. StraubeDr John F. StraubeAssistant ProfessorAssistant Professor

Dept of Civil Engineering & School of ArchitectureDept of Civil Engineering & School of Architecture

University of WaterlooUniversity of WaterlooOntario, CanadaOntario, Canada

www.civil.uwaterloo.cawww.civil.uwaterloo.ca/beg/[email protected] 519 888 [email protected] 519 888 4015


Overview of PresentationOverview of Presentation

? Why?? Vapor in air? Vapour barriers? Air Barriers? Understanding Driving Forces? Details of air barriers and airflow


Moisture PhasesMoisture Phases

? As for most materials? All four phases

occur commonly in buildings

? AB and VB are interested in vaporform only

GasGas(water vapour,

steam)

frost

sublimateevaporate

condense

freeze

thaw

desorbadsorb

Adsorbed

Liquid(water)

Solid(ice)


Wall Wetting MechanismsWall Wetting Mechanisms

1. Rain Absorptionsplash and drips

3. Built in Moisture3. Built in Moisture

2. Water 2. Water VapourVapouri) Diffusioni) Diffusionii) Convection ii) Convection

(air leaks)(air leaks)

4. Wicking 4. Wicking (from ground)(from ground)


Why use with AB or VBWhy use with AB or VB

? 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


Water Vapour PressureWater Vapour Pressure


Vapour PressureVapour 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

Warm surface


CondensationCondensation


Water Vapour in AirWater Vapour 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 thepsychrometric chart

© John Straube 200111 © John Straube 200112-10.0 -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

4000V

ap

ou

r P

res

su

re (

Pa

)

100% RH75% RH50% RH25% RH

Psych Chart: Air Vapour Content vs Temperature

Saturation

50%RH

25%RH

75%

RH

100%

RH

100%RH

Temperature

Air

Moi

stur

e C

onte

nt

= va

pour

pres

sure

(Pa,

in H

g),

hum

idity

rat

io (g

/kg,

gra

ins/

pd)

-10 ºC14 º F

0 ºC32 º F

10 ºC50 º F

20 ºC68 º F

30 ºC86 º F

40 ºC104º F


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

© John Straube 200115-10.0 -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

Vap

ou

r P

ressu

re (

Pa)

100% RH75% RH50% RH25% RH

Indoor Conditions

• 18 - 26°C / 65 – 78°F• 25 to 60%RH(Could be 20 to 70%)

Summer

Winter

-10 ºC14 º F

0 ºC32 º F

10 ºC50 º F

20 ºC68 º F

30 ºC86 º F

40 ºC104º F © John Straube 200116

-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

Vap

ou

r P

ressu

re (

Pa)

100% RH75% RH50% RH25% RH

Outdoor ConditionsBurlington, VT•January -10°C / 14°F & 80%•• July 20°C/July 20°C/ 68°F & 75%68°F & 75%

-10 ºC14 º F

0 ºC32 º F

10 ºC50 º F

20 ºC68 º F

30 ºC86 º F

40 ºC104º F

© John Straube 200117-10.0 -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

Vap

ou

r P

ressu

re (

Pa)

100% RH75% RH50% RH25% RH

Indoor vs Outdoor Conditions

Summer

Winter

VapourPressureDifference

Inward drive can be as big as outward

-10 ºC14 º F

0 ºC32 º F

10 ºC50 º F

20 ºC68 º F

30 ºC86 º F


Why use an AB or VB?Why use an AB or VB?

?? Code requirementCode requirement• NBCC -> OBC requires AB/VB if damage can occur• VB only required sometime, AB almost all times

?? VB VB only only helpshelps controlcontrol interstitialinterstitialcondensationcondensation

? AB about interstitial condensation and• comfort• energy• sound• odour/smoke


Diffusion and ConvectionDiffusion and Convection

?Water vapour moves by

1. vapour diffusionmore to less vapour

2. air convectionmore to less air pressure

vapour is along for the ride


In the beginningIn the beginning

• Find the vapour barrier


Old AssembliesOld Assemblies

? Integral vapour resistance? Massive moisture storage

MasonryMasonry

PlasterPlaster

No No vapourvapourbarrier of coursebarrier of course


Old Framed AssembliesOld Framed Assemblies

? Little to some vapour resistance? Little moisture storage? Little insulation / air leaky = dry!

tt

No No vapourvapourbarrier of coursebarrier of course


Changes . . .Changes . . .

? Increase in wood frame, esp. post WW1? Began to add insulation

• comfort

• wood scarcity, coal

? Moisture problems in cold climatesnoted in 1930’s

? Paint peeling of siding

tt


Dr Frank RowleyDr Frank Rowley

? 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


The One US PermThe One US Perm

? “Test house” inside climate chamber

--29 C/29 C/--20 F20 F

21 C/ 70 F40% RH

No VB:No VB:21.5 g/m21.5 g/m22/day /day (0.07 ounce/ft(0.07 ounce/ft22/day) /day)

This research resulted in 1 perm / 60 ng/Pa s m2 or less vapor barriers

ASH&VE Transactions No 44, “Condensation Within Walls” 1938 © John Straube 200126

The Sales Job 1940The Sales Job 1940--19601960

? 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”


Vapour BarriersVapour Barriers

? Vapour barriers in Code: <1 US perm• 1942 first reference

? Canadian codes – as of 1975 ? Vapour retarder approx 2-5 US perm? Measurement Units

• Metric perms ng /(s·m2·Pa)

• US perm grain/(hr·in Hg· ft2)• WVT grams/(sq ft/24 hours)


Air barriers discoveredAir 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? Why poly?

? Poly is cheap and easy? Cliff Shirtcliff

• Insulation shortage

• Paper-facings hide insulation


When and whereWhen and where

? 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


Some rules: When and WhereSome 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


Cold

Severe Cold

Hot-Dry

Mixed-Humid

Joe Lstiburek’s Builders Guides


Climate and VBClimate 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



? 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 designVB and Wall design

? 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


Water Water VapourVapour DiffusionDiffusion

More More VapourVapour

LessLessVapourVapour

Cold weatherCold weather

VapourVapourDiffusionDiffusion

Warm humid weatherWarm humid weather


CondensationCondensation

Cold Surface


Vapour DiffusionVapour 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


Vapour DiffusionVapour 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

© John Straube 20013950 F 68 F32 F © John Straube 200140

Air leakage Air leakage vsvs DiffusionDiffusion

? Air leakage is much more critical

? Walls sensitive to diffusion-related condensation will be more sensitive to air leakage

© John Straube 200141 © John Straube 200142-10.0 -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

Vap

ou

r P

ressu

re (

Pa)

100% RH75% RH50% RH25% RH

Air Leakage vs Diffusion

Summer

Winter

Air LeakageCondensation

Diffusion

50%RH

25%RH

75%

RH

100%

RH


Solution to Interstitial CondensationSolution to Interstitial Condensation

? Air leakage – install air barriers and insulated sheathing

? Vapor diffusion – choose materials, insulated sheathing, and/or install vapor barrier


Wall with Insulated SheathingWall with Insulated Sheathing


Warm = No Warm = No CondensationCondensation

Sheathing Air Permeable Insulation










CalculationsCalculations

? Simple calculations can used to understand the issue

? Computer models are useful for complex situations


Vapour BarriersVapour Barriers

? Vapour barriers in Code: <1 US perm• based on Rowley 1937 • no good science

? Vapour retarder approx 2-5 US perm? Measurement Units

• Metric perms ng /(s·m2·Pa)

• US perm grain/(hr·in Hg· ft2)• WVT grams/(sq ft/24 hours)


LowLow--perm Materialsperm 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)


MidMid--perm Materialsperm Materials

? Plywood 0.5 to 20 (dry to wet)? Expanded foam 2.5 - 5 perms for 1 inch? Spray PUR about 2 perms? Drywall with latex paint (2-5 perms)


HighHigh--perm Materialsperm Materials

? Fibreboard over 20? Plywood 0.5 to 20 (dry to wet)? Icynene open cell spray foam 10 - 13? Tyvek other housewraps 20 to 50 perms? Building paper over 10 to 30


VapourVapour Permeance: SheathingPermeance: Sheathing

0

500

1000

1500

2000

2500

0 0.2 0.4 0.6 0.8 1

Relative Humidity

Per

mea

nce

(n

g/P

a s

m2) 11.1 mm OSB

12.7 mm Plywood

Dry

Cu

p

Wet

Cu

p


When and WhereWhen and Where

? 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


Cold

Severe Cold

Hot-Dry

Mixed-Humid

Joe Lstiburek’s Builders Guides© John Straube 200154


? 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



? 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










Wall w/o Insulated SheathingWall w/o Insulated Sheathing


Cold = Cold = CondensationCondensation





Warm = No Warm = No CondensationCondensation



DryingDrying

? Vapour barriers stop wetting and drying? Overkill (e.g. poly) can cause problems!? Inward drying is useful in many climates


Vapor flows in both directionsVapor flows in both directions

? Vapour 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


Inward DrivesInward Drives

? Long understood by researchers“When a vapour barrier is used, the wall can loose “When a vapour barrier is used, the wall can loose

moisture only to the outside. In summer, hot sun moisture only to the outside. In summer, hot sun following a rain drives moisture as vapour to the inside following a rain drives moisture as vapour to the inside of the wall, and condensation behind the vapour barrier of the wall, and condensation behind the vapour barrier can occur.” Hutcheon can occur.” Hutcheon 19531953

? 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”


Inward DiffusionInward Diffusion

2.Vapour drives inward

3.Condensation on “cold” surfaces

1. Temperature and solar heating warms

wet material

WettingWettingIf If imimpermeablepermeable

DryingDryingIf permeableIf permeable3.Vapour dries to inside

© John Straube 200163-10.0 -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

Vap

ou

r P

ressu

re (

Pa)

100% RH75% RH50% RH25% RH

Indoor Conditions

• 18 - 26°C / 65 – 78°F• 25 to 60%RH(Could be 20 to 70%)

Summer

Winter

-10 ºC14 º F

0 ºC32 º F

10 ºC50 º F

20 ºC68 º F

30 ºC86 º F


© John Straube 200165 © John Straube 200166

VapourVapour Control StrategiesControl 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


Air movementAir movement

? 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


ChannelChannel


DiffuseDiffuse


TortuousTortuous


Glass is a perfect VB



Airflow Control: WhatAirflow 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: WhyAirflow Control: Why

? Condensation wetting ? Drafts (= comfort)? Energy ? Pollutant transport - smell, particles, gas? Sound

? NOT just energy!!


Airflow Control: WhereAirflow 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 LeakageAir 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


Air leakage Air leakage (Convection)(Convection)

More More PressurePressure

LessLessPressurePressure

Cold WeatherCold Weather


Warm WeatherWarm Weather

More More PressurePressure

CondensationCondensationif more if more vapourvapour

Cold Surface© John Straube 200178

Air Barrier SystemsAir 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 continuousThey leak at joints, interfaces, penetrations

? multiple air barrier planes are useful for redundancy


Air Barrier SystemsAir Barrier Systems

? Continuous• primary need

? Strong• designed for full wind load

? Durable• critical component - repair, replacement

? Stiff• control billowing, pumping

? Air Impermeable • (may be vapour permeable)


Stapled Paper is not an air barrier


Control Air Leakage CondensationControl 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 Leaks1. Stop Leaks

“Find the holes and plug them”This requires finicky attention to 3-D

details.

© John Straube 200183Typical Air Leakage Points



Air sealing around windows andotheropenings


A small hole in the air barrier


Poly can be (?) an air and vapour barrier

© John Straube 200189 © John Straube 200190Beware: poly is a VB Beware: poly is a VB ---- keep on warm sidekeep on warm side


Use drywall, framing members• Seal with sealant, gaskets, etc.•Is stiff, strong•Often easier to get better

Drawing From: Dr. Joe LstiburekBuilders Guide

The Airtight Drywall Approach



ADA Detail ADA Detail WindowWindow

From NRCan Super-E


ADA Detail ADA Detail Rim JoistRim Joist

From NRCan Super-E


2. Control Temperatures2. Control Temperatures

A potent cold-climate strategy for framed enclosure systems


Insulated Sheathing 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 vapourdrives, e.g., they have permeances of M<200

? Some sheathings are vapour impermeable --they reduce drying outward!

? RememberInsulated Sheathing = Moisture Control Strategy


Wall w/o Insulated SheathingWall w/o Insulated Sheathing

Air Air leakageleakage


Cold = Cold = CondensationCondensation



Air Air leakageleakage


Warm = no Warm = no condensationcondensation


3. Control Driving Pressures3. Control Driving Pressures

Wind+stack: understand them.Control HVAC pressures!

Control stack by compartmentalizationReduce interior vapor content


Driving ForcesDriving Forces

Wind Effect Stack Effect Combustion and Ventilation


WindWind

? 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 Speed DistributionWind Speed Distribution

0%

5%

10%

15%

20%

25%

30%

00 22 44 66 88 1010

Wind Speed (m/s)Wind Speed (m/s)

Rel

ativ

e Fr

eque

ncy

Rel

ativ

e Fr

eque

ncy

Avg. 3.6 m/s = 8 mphAvg. 3.6 m/s = 8 mph

1/10 yr cladding: 1 sec/10 yr1/10 yr cladding: 1 sec/10 yr1/30 yr structure: 3 sec/ 30 yr1/30 yr structure: 3 sec/ 30 yr

For Waterloo, CanadaFor Waterloo, Canada


WindspeedWindspeedVaries with Height and ExposureVaries with Height and Exposure


Wind speed to PressureWind speed to Pressure? Wind Velocity to Pressure:

• Pstag = 0.647 ? V2 [in Pa and m/s]• Lowrise Velocity @ 10 m= 4 m/s 10 Pa

• Highrise Velocity @ 50 m=8 m/s 40 Pa

VelocityVelocityStagnation PressureStagnation Pressure


Flow PatternsFlow Patterns


Pressure Distribution on FacePressure Distribution on Face

PeakSuctions at Sides+


Wind Pressures / Flow PatternsWind Pressures / Flow Patterns

•• Pressure on windward sidePressure on windward side•• Suction on lee and sidewallsSuction on lee and sidewalls


Wind Pressure DistributionWind Pressure Distribution

Plan View

?? PP


Stack EffectStack Effect

? Hot air rises? Tall Building in Winter = Heavy Balloon

+


Stack EffectStack Effect

? “Perfect” Building equally leaky everywhere? Neutral Pressure Plane at mid-height

+

NPPNPP

Cold weather exampleCold weather example


Stack Pressure DistributionStack Pressure Distribution

Pressures at a Pressures at a specific heightspecific height

Stack EffectStack EffectPressuresPressures


WindStackRain


PressurizationPressurization

? More airflow forced into building than sucked out of building = Pressurization

+

Fan


DeDe--PressurizationPressurization

? More airflow forced out of building than forced into building = De-Pressurization

Fan


Pressure DistributionPressure Distribution

Wind Pressures

Stack Pressure +Stack Pressure +HVACHVAC

PressuresPressures

Combined Combined PressuresPressures


Control HVAC EffectsControl 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 EnclosuresAirflow Within Enclosures



Plan View

?? PP



Plan View

?? PP


Lateral AirflowsLateral Airflows

Punched Steel Studs

Condensation inside (cold)Condensation backside (hot)


Internal Internal Stack Effect & InsulationStack Effect & Insulation

Hot air = lightHot air = light

Cold air = heavyCold air = heavy

•• Gaps in batt Gaps in batt insulation on insulation on both sidesboth sides

••Stapled paper!Stapled paper!

Air gapsBatt

Inside

Outside

Common performance problem


Internal Internal Stack EffectStack Effect




Result: Air Result: Air FlowFlow

•• Gaps in batt Gaps in batt insulation on insulation on both sidesboth sides

•• closed circuitclosed circuit

•• energy costenergy cost

•• cold surfacescold surfaces


Air movement Air movement (Stack Effect)(Stack Effect)


Result: Air Result: Air FlowFlow




Air movement Air movement (Stack Effect)(Stack Effect)



Air FlowAir Flow

Warm WeatherWarm Weather



Cold Surface© John Straube 2001126

Airflow within enclosuresAirflow 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


WindwashingWindwashing

? Need some airtightness outside permeableinsulation

? 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


Control lateral flowControl lateral flow

Airflow behind cladding causes cooling or "wind washing" of air permeable insulations

Pressure Profile

Suction on sides

Framing members and compartment seperators control air flow

Pressure Profile

Suction on sides


Using ExteriorUsing ExteriorSheathing as airSheathing as airBarrierBarrier

Not

Not


How long will the tape last?


HVAC InteractionHVAC Interaction


WarmWarmMoistMoistAirAir The Air+ The Air+

Thermal BarrierThermal Barrier

HVAC: The Way it is DesignedHVAC: The Way it is Designed

+

Air Handler

100 100 cfmcfm100 100 cfmcfm

Perfect ductsPerfect ducts


WarmWarm

MoistMoistAirAir

The Air+ The Air+ Thermal BarrierThermal Barrier

HVAC : The Way it “Works”HVAC : The Way it “Works”

+

Air Handler

100 100 cfmcfm80 80 cfmcfm

20 20 cfmcfm leakageleakage

20 20 cfmcfm


DepressurizationDepressurization = Air leakage= Air leakageWarm ClimateWarm Climate

More More PressurePressureWarmWarmHumidHumid

Cold Surface

LessLessPressurePressureCoolCool



HVAC SolutionsHVAC Solutions

? Hot-humid climates •• pressurizepressurize with conditioned outdoor air

? Cold climates •• depressurizedepressurize by exhausting air

? properly sized transfer grilles (small ? P) ? keep ducts inside! (or seal ducts)? Good air barrier systems for the enclosure


Internal Moisture LoadsInternal 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% ?


Air Vapour Content vs Temperature

0

2000

4000

0 20 40 60 80 100

Temperature (F)

Air

Mos

itur

e C

onte

nt =

Vap

our

Pre

ssur

e

Saturation

80%RH

60%RH

Winter

Summer

Air LeakageCondensation

Reduce moisture loads= reduced condensation


Control Interior RH!Control Interior RH!

Cold Climate? Air-to-Air Heat exchanger? Exhaust ventilation


Interior Air MoistureInterior Air Moisture

Moisture Removal (ventilation, leakage, diffusion?)

Outdoor Air PlusMoisture Production

? Ventilation and Diffusion Remove Moisture

2020--60%RH60%RH

100%RH100%RH


Sources of Moisture Within Buildings

Source Strength kg per day

People - evaporation per person 0.9 to 1.25 *

Humidifier 2-20+

Hot tub, Whirlpool 2-20+

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 / m2

Unvented Gas Appliance (ea) 1

Seasonal Desorption 3-8 depends on the type of construction

Plants/Pets 0.2 - 0.5 (five small plants or one dog)

Total (Typical Family of 4) About 10 , but potential ranges 3 to 40© John Straube 2001142

Internal MoistureInternal 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


0%

20%

40%

60%

80%

100%

0 1 2 3 4Air Changes per Hour

Ind

oo

r R

H

5102040

Moisture Production Rate (kg/day)

For Outdoor Conditions of +5 C/80%RH

0.1 ACH

For 775 sf Apartment


Mechanical VentilationMechanical 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


Interior MoistureInterior 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 DryingWetting and Drying

?? Air leakageAir leakage and DiffusionDiffusion can cause • Wetting AND

• Drying•• DependsDepends on Weather Conditions!

? Vapour barriers and air barriers reduce or slow flow in BOTH directions

?? allall vapourvapour barriers slow inward dryingbarriers slow inward drying?? allall vapourvapour resistant claddings and sheathings slow resistant claddings and sheathings slow

outward dryingoutward drying


ConclusionsConclusions

? Air barriers and vapour barriers are different• can be combined in same materials

? Vapour 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!


Review Air Barrier SystemsReview Air Barrier Systems

? Continuous• primary need

? Strong• designed for full wind load

? Durable• critical component - repair, replacement

? Stiff• control billowing, pumping

? Air Impermeable • (may be vapour permeable)


ReviewReview

? Air Barrier or Vapour Barrier? When?• Tyvek

• Concrete wall• Steel roof• Poly• Drywall• Peel and stick membrane• Blue Extruded Styrofoam


ReviewReview

? Where to place the VB in• Miami

• Minnespolis

? Where to place the ABS• Miami• Minneapolis

Documents

Air and Vapour Barriers - Overview of Presentation Who ... Comfort Air Vapour barri… · • Use lower perm insulation (foam)?If moderate, use retarder, like paint?Insulated sheathing