vapor barriers & vapor retarders - sprayfoam.org barriers vapor retarders.pdf · vapor barriers...

29
Vapor Barriers & Vapor Retarders Presented by Roger V. Morrison, PE, RRC Deer Ridge Consulting, Inc.

Upload: vudieu

Post on 28-Aug-2018

247 views

Category:

Documents


0 download

TRANSCRIPT

Page 1: Vapor Barriers & Vapor Retarders - sprayfoam.org Barriers Vapor Retarders.pdf · Vapor Barriers & Vapor Retarders Presented by ... Psychrometrics 3. Vapor barriers and vapor retarders

Vapor Barriers & Vapor

Retarders

Presented by

Roger V. Morrison, PE, RRC

Deer Ridge Consulting, Inc.

Page 2: Vapor Barriers & Vapor Retarders - sprayfoam.org Barriers Vapor Retarders.pdf · Vapor Barriers & Vapor Retarders Presented by ... Psychrometrics 3. Vapor barriers and vapor retarders

What we’re gonna talk about

1. Water vapor drive and transmission

2. Psychrometrics

3. Vapor barriers and vapor retarders

4. SPF vapor transmission properties

5. Best practices

6. Analytical techniques

Page 3: Vapor Barriers & Vapor Retarders - sprayfoam.org Barriers Vapor Retarders.pdf · Vapor Barriers & Vapor Retarders Presented by ... Psychrometrics 3. Vapor barriers and vapor retarders

Water Vapor Transmission

Fundamentals

• Basic flow equation

• Flow = drive / resistance= drive x permeance

• D = P x M

– D = water vapor diffusion

– P = water vapor pressure (absolute humidity)

– M = permeance

Page 4: Vapor Barriers & Vapor Retarders - sprayfoam.org Barriers Vapor Retarders.pdf · Vapor Barriers & Vapor Retarders Presented by ... Psychrometrics 3. Vapor barriers and vapor retarders

Fundamentals (cont)

• Diffusion

– Water vapor molecules wending their

way through solid or porous materials

• Drive

– Water vapor moves from regions of high

humidity to regions of lower humidity

– Absolute humidity is the driving force

Page 5: Vapor Barriers & Vapor Retarders - sprayfoam.org Barriers Vapor Retarders.pdf · Vapor Barriers & Vapor Retarders Presented by ... Psychrometrics 3. Vapor barriers and vapor retarders

Fundamentals (cont)

• Permeance

– Tendency of a material to allow water

vapor to diffuse through it

– Dependent on:

• Physical properties of the material

(permeability)

• Thickness

Page 6: Vapor Barriers & Vapor Retarders - sprayfoam.org Barriers Vapor Retarders.pdf · Vapor Barriers & Vapor Retarders Presented by ... Psychrometrics 3. Vapor barriers and vapor retarders

Fundamentals (cont)

• Permeance

– The tendency of a material to allow the

passage of water vapor at a specified

thickness

– Permeance values MUST report the thickness

Grains H O

ft hr in HgPerm2

2

Note: 1 pound = 7000 grains

Page 7: Vapor Barriers & Vapor Retarders - sprayfoam.org Barriers Vapor Retarders.pdf · Vapor Barriers & Vapor Retarders Presented by ... Psychrometrics 3. Vapor barriers and vapor retarders

Fundamentals (cont)

• Permeability

– The tendency of a material to allow the

passage of water vapor

– NOT thickness dependent; thicknesses are

NOT reported

– Divide by the actual thickness to determine the

Permeance

Grains H O in

ft hr in HgPerm inch2

2

Page 8: Vapor Barriers & Vapor Retarders - sprayfoam.org Barriers Vapor Retarders.pdf · Vapor Barriers & Vapor Retarders Presented by ... Psychrometrics 3. Vapor barriers and vapor retarders

Fundamentals (cont)

• Permeance (perm)

• Specify the

thickness when

reporting this

value

Grains H O

ft hr in Hg

2

2

• Permeability

(perm-inch)

• Divide by the

thickness to get

permeance

Grains H O in

ft hr in Hg

2

2

Page 9: Vapor Barriers & Vapor Retarders - sprayfoam.org Barriers Vapor Retarders.pdf · Vapor Barriers & Vapor Retarders Presented by ... Psychrometrics 3. Vapor barriers and vapor retarders

Psychrometrics

• Warm air can hold more water vapor

than cold air

• Air can become saturated with water

vapor (Condensation)

• The saturation threshold increases

with temperature

Page 10: Vapor Barriers & Vapor Retarders - sprayfoam.org Barriers Vapor Retarders.pdf · Vapor Barriers & Vapor Retarders Presented by ... Psychrometrics 3. Vapor barriers and vapor retarders

Psychrometric Chart

TEMPERATURE

ABSOLUTE HUMIDITY

SATURATION

100% REL HUMIDITY

50% REL HUMIDITY

Page 11: Vapor Barriers & Vapor Retarders - sprayfoam.org Barriers Vapor Retarders.pdf · Vapor Barriers & Vapor Retarders Presented by ... Psychrometrics 3. Vapor barriers and vapor retarders

Psychrometric Chart

Page 12: Vapor Barriers & Vapor Retarders - sprayfoam.org Barriers Vapor Retarders.pdf · Vapor Barriers & Vapor Retarders Presented by ... Psychrometrics 3. Vapor barriers and vapor retarders

SPF is a very useful material

to control temperature and

humidity profiles in building

assemblies

Page 13: Vapor Barriers & Vapor Retarders - sprayfoam.org Barriers Vapor Retarders.pdf · Vapor Barriers & Vapor Retarders Presented by ... Psychrometrics 3. Vapor barriers and vapor retarders

More Fundamentals

• Water vapor concentration (absolute

humidity) can build up within

building assemblies due to water

vapor drive

• Condensation occurs when the

temperature within the assembly

drops below the dew point

Page 14: Vapor Barriers & Vapor Retarders - sprayfoam.org Barriers Vapor Retarders.pdf · Vapor Barriers & Vapor Retarders Presented by ... Psychrometrics 3. Vapor barriers and vapor retarders

More Fundamentals (cont)

• AVOID condensation by:

– Preventing building components from

dropping below the dew point

– Reducing water vapor entering the

building component

– Increasing water vapor leaving the

building component

Page 15: Vapor Barriers & Vapor Retarders - sprayfoam.org Barriers Vapor Retarders.pdf · Vapor Barriers & Vapor Retarders Presented by ... Psychrometrics 3. Vapor barriers and vapor retarders

More Fundamentals (cont)

• Preventing building components from dropping below the dew point

• Reducing water vapor entering the building component

• Increasing water vapor leaving the building component

• Placing INSULATION on the cold side of vapor retardant materials

• Installing vapor RETARDANT materials on the warm side of the assembly

• Installing BREATHABLE materials on the cold side of the assembly

Avoid condensation by:

Page 16: Vapor Barriers & Vapor Retarders - sprayfoam.org Barriers Vapor Retarders.pdf · Vapor Barriers & Vapor Retarders Presented by ... Psychrometrics 3. Vapor barriers and vapor retarders

Barriers & Retarders

• The definition keeps changing

• “Vapor Retarder” is the preferred

term but you’ll commonly hear the

term “Vapor Barrier”

• Common definition:

Vapor retarder ≤ 1 perm

• Not a very good definition

Page 17: Vapor Barriers & Vapor Retarders - sprayfoam.org Barriers Vapor Retarders.pdf · Vapor Barriers & Vapor Retarders Presented by ... Psychrometrics 3. Vapor barriers and vapor retarders

Vapor Barriers & Retarders

Impermeable Class I VR < 0.1 perm

Semi-

Impermeable

Class II VR 0.1 – 1.0 perm

Semi-Permeable Class III VR 1.0 – 10.0 perm

Permeable > 10.0 perm

Page 18: Vapor Barriers & Vapor Retarders - sprayfoam.org Barriers Vapor Retarders.pdf · Vapor Barriers & Vapor Retarders Presented by ... Psychrometrics 3. Vapor barriers and vapor retarders

Vapor Barriers & Retarders

0.1

1.0

10

Polyethylene

Metal Foils

Butyl Coatings

Roof Membranes

SPF (closed-cell) > 2”

Kraft Paper Laminate

Plywood

Vinyl Coverings

SPF (closed-cell) < 2”

SPF (open-cell) > 2”

Polystyrene Foam

Acrylic/Silicone Coatings

SPF (open-cell) < 2”

Sheetrock

Fiberglass

Page 19: Vapor Barriers & Vapor Retarders - sprayfoam.org Barriers Vapor Retarders.pdf · Vapor Barriers & Vapor Retarders Presented by ... Psychrometrics 3. Vapor barriers and vapor retarders

Spray Foam Properties

• Closed-cell, 2 pcf SPF

– Permeability = 1.8 perm-in

– Permeance = 0.9 perm @ 2”

• Open-cell, ½ pcf SPF

– Permeability = 15 perm-in

– Permeance = 4.3 perm @ 3.5”

Page 20: Vapor Barriers & Vapor Retarders - sprayfoam.org Barriers Vapor Retarders.pdf · Vapor Barriers & Vapor Retarders Presented by ... Psychrometrics 3. Vapor barriers and vapor retarders

SPF: Retarder or Not?

0.1

1.0

10

1” ocSPF (15)

2” ocSPF (7.5)

3.5” ocSPF (4.3)

6” ocSPF (2.5)

1” ccSPF (1.8)

2” ccSPF (0.90)

3.5” ccSPF (0.51)

6” ccSPF (0.30)

Page 21: Vapor Barriers & Vapor Retarders - sprayfoam.org Barriers Vapor Retarders.pdf · Vapor Barriers & Vapor Retarders Presented by ... Psychrometrics 3. Vapor barriers and vapor retarders

Theory of Relativity

• Water vapor retardance is relative:

When determining the need for and

type of vapor retarder, consideration

must be given to all the other

materials with which it is assembled.

• What may be a retarder in one case

may be considered a breather in

another.

Page 22: Vapor Barriers & Vapor Retarders - sprayfoam.org Barriers Vapor Retarders.pdf · Vapor Barriers & Vapor Retarders Presented by ... Psychrometrics 3. Vapor barriers and vapor retarders

Best Practices

When this cannot be done, install a vapor

retarder such that the vapor retarder is

positioned as close to the side with the

highest absolute humidity as possible and

the vapor retarder has an installed perm

rating substantially less than that of the

next lowest component.

Install the building materials such that relative

vapor retardance increases toward the side

with the higher absolute humidity (usually the

warm side).

Page 23: Vapor Barriers & Vapor Retarders - sprayfoam.org Barriers Vapor Retarders.pdf · Vapor Barriers & Vapor Retarders Presented by ... Psychrometrics 3. Vapor barriers and vapor retarders

Analytical Techniques

• Dew Point Analysis

• WUFI Simulation

Page 24: Vapor Barriers & Vapor Retarders - sprayfoam.org Barriers Vapor Retarders.pdf · Vapor Barriers & Vapor Retarders Presented by ... Psychrometrics 3. Vapor barriers and vapor retarders

Dew Point AnalysisRoof ProfileTemperature ProfileHumidity ProfileDesign ConditionsExterior

10o F

50 % RH

Interior

70o F

40 % RH

Dew Point

Condensation

Saturation

Line

Calculated

Humidity

Line

T TR

RT Tx i

x

i elog logP AB

TC TP P

M

MP Px i

x

i e

( / )

( / )

1

1

Page 25: Vapor Barriers & Vapor Retarders - sprayfoam.org Barriers Vapor Retarders.pdf · Vapor Barriers & Vapor Retarders Presented by ... Psychrometrics 3. Vapor barriers and vapor retarders

WUFI Simulation

Page 26: Vapor Barriers & Vapor Retarders - sprayfoam.org Barriers Vapor Retarders.pdf · Vapor Barriers & Vapor Retarders Presented by ... Psychrometrics 3. Vapor barriers and vapor retarders

Review

• Water vapor moves from regions of

high absolute humidity to regions of

lower absolute humidity

• Rate of vapor movement is

determined by the permeance of the

building assembly components

Page 27: Vapor Barriers & Vapor Retarders - sprayfoam.org Barriers Vapor Retarders.pdf · Vapor Barriers & Vapor Retarders Presented by ... Psychrometrics 3. Vapor barriers and vapor retarders

Review (cont)

• Problems are likely to occur if

condensation occurs

• Condensation can be avoided by the

judicious use and placement of

insulation and breathable and

retardant materials

Page 28: Vapor Barriers & Vapor Retarders - sprayfoam.org Barriers Vapor Retarders.pdf · Vapor Barriers & Vapor Retarders Presented by ... Psychrometrics 3. Vapor barriers and vapor retarders

Review (cont)

• SPF can be used to control both

thermal and humidity profiles in

building assemblies to avoid

condensation

• Analytical techniques may be used to

predict condensation potential in

building assemblies

Page 29: Vapor Barriers & Vapor Retarders - sprayfoam.org Barriers Vapor Retarders.pdf · Vapor Barriers & Vapor Retarders Presented by ... Psychrometrics 3. Vapor barriers and vapor retarders