Let's Get Real:
A Practical Approach to Water Vapor Transmission Measurement on Air Barriers
Rick LeFevre
Senior R&D Chemist
Dryvit Systems, Inc.
West Warwick, RI
2013 ABAA Technical Conference
R. LeFevre Dryvit Systems, Inc.
2013 ABAA Technical Conference
R. LeFevre Dryvit Systems, Inc.
Q: What is Perm?
1 US Perm = 1 grain of water vapor per hour, per square foot, per inch of mercury.
mass
time
area
pressure
A measure of water vapor movement through a material
2013 ABAA Technical Conference
R. LeFevre Dryvit Systems, Inc.
Q: At what Perm is a Material a Vapor Retarder?
Early 1990's USDA Forest Products Laboratory Testing
A: less than or equal to 1.0 Perm!
Inside
Outside
2013 ABAA Technical Conference
R. LeFevre Dryvit Systems, Inc.
Water/ Water Vapor Drive
Vapor Retarder (1.0 Perm or less)
Vapor Retarder (1.0 Perm or less)
Water/ Water Vapor Drive
Q: Why was/is Barrier Perm an Important Property to Test for?
2013 ABAA Technical Conference
R. LeFevre Dryvit Systems, Inc.
abaa
air barrier
association of
america
avpbaa
air & vapor permeable barrier
association of
america
Name | Air aka N2, O2 |
Crime | Building Damage |
Charge | Accessory to Crime |
Sentence | Air Barrier |
Name | Water Vapor aka H2O |
Crime | Building Damage |
Charge | Perpetrator of Crime |
Sentence | Air Barrier |
Sentence 2 | Vapor Permeable Barrier |
2013 ABAA Technical Conference
R. LeFevre Dryvit Systems, Inc.
Document Name: ASTM E96: Standard
Test Methods for Water
Vapor Transmission of
Materials
CFR Section(s): 24CFR 3280.504(a)
Standards Body: American Society for
Testing and Materials
2013 ABAA Technical Conference
R. LeFevre Dryvit Systems, Inc.
Q: What materials are/were normally tested to E96 as originally written?
Paper
Plastic Films
Other Sheet Materials
Fiberboards
Gypsum and Plaster Products
Wood Products
Plastics
2013 ABAA Technical Conference
R. LeFevre Dryvit Systems, Inc.
Q: What does the sample test assembly look like?
Thick Barriers: PUR Foam, Rigid Cellular Boardstock
Thin Barriers: Building Wraps, Self-Adhered Sheet
Thin Barriers: Fluid Applied Membranes
2013 ABAA Technical Conference
R. LeFevre Dryvit Systems, Inc.
2013 ABAA Technical Conference
R. LeFevre Dryvit Systems, Inc.
A Simple and Reproducible Method to Fairly Measure E96 "B" Perms on any Air Barrier
2013 ABAA Technical Conference
R. LeFevre Dryvit Systems, Inc.
2013 ABAA Technical Conference
R. LeFevre Dryvit Systems, Inc.
2013 ABAA Technical Conference
R. LeFevre Dryvit Systems, Inc.
2013 ABAA Technical Conference
R. LeFevre Dryvit Systems, Inc.
2013 ABAA Technical Conference
R. LeFevre Dryvit Systems, Inc.
mass
time
area
pressure
PROCEED TO PERM CALCULATION.........
2013 ABAA Technical Conference
R. LeFevre Dryvit Systems, Inc.
vapor pressure differential drives moisture vapor transmission (MVT)
72F
100% RH
72F
50% RH
Perm is the inverse resistance to MVT
2013 ABAA Technical Conference
R. LeFevre Dryvit Systems, Inc.
Perm =
MVT
time
mass
area
p
S x (R1-R2)
72F
100% RH
72F
50% RH
saturation vapor pressure
=
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R. LeFevre Dryvit Systems, Inc.
Sheathing (DensGlass Gold)
area
pressure
mass
time
Perm = 31.5
2013 ABAA Technical Conference
R. LeFevre Dryvit Systems, Inc.
Sheathing (DensGlass Gold) with Fluid Applied Membrane
Perm = 1.5
2013 ABAA Technical Conference
R. LeFevre Dryvit Systems, Inc.
Sheathing Perm
Fluid Applied Membrane Perm
Use a "Fox Equation" to Calculate the Membrane Layer Perm!
Fluid Applied Membrane and Sheathing Assembly Perm
1
1
1
1.5
31.5
Fluid Applied Membrane Perm
1.6
2013 ABAA Technical Conference
R. LeFevre Dryvit Systems, Inc.