ASTM E3127-24

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: E3127 − 22 E3127 − 24
Standard Guide for
Specifying Water Vapor Transmission Material Properties of
Water-Resistive Barriers and Air Barriers
This standard is issued under the fixed designation E3127; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This document providescovers guidelines for specifying water vapor transmission (WVT) properties for above-grade
water-resistive barriers and air barriers (WRB/AB), typically installed between building structural components and cladding that
compose the exterior side of building envelopes in North America.
1.2 This guide applies to all types of water-resistive barrier and air barrier products, including multifunctional products, regardless
of the manufacturing process, type of material, or installation technique.
1.3 This guide provides general provisions for specifying and reporting the water vapor transmission properties of WRB/AB
determined by standardized test methods, in accordance with in-service conditions these products typically experience within
building envelopes.
1.4 It is beyond the scope of this guide to optimize the water vapor transmission characteristics of WRB/AB for specific conditions
of use. The specific conditions of use should account for variations in indoor and outdoor climates, cladding type, moisture storage
capacity of cladding materials, thermal insulating measures for wall and roof assemblies, air movement, and vapor diffusion control
strategies.
1.5 This guide does not address proper installation and integration of WRB/AB with other wall and roof components.
1.6 The values stated in inch-pound units are to be regarded separately as standard. Within the text, the SI units shown in
parentheses are provided for information only. The values stated in each system are not exact equivalents; therefore, each system
shall be used independently. Combining values from two systems may result in non-conformance with the standard. However,
derived results can be converted between systems using appropriate conversion factors (see Table 1).
1.7 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of
regulatory limitations prior to use.
1.8 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
This guide is under the jurisdiction of ASTM Committee E06 on Performance of Buildings and is the direct responsibility of Subcommittee E06.41 on Air Leakage and
Ventilation Performance.
Current edition approved May 1, 2022March 1, 2024. Published July 2022March 2024. Originally approved in 2022. Last previous edition approved in 2022 as E3127 – 22.
DOI: 10.1520/E3127-22.10.1520/E3127-24.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
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A, B
TABLE 1 Units and Conversion Factors
To Obtain (for the
Multiply By
same test condition)
C
WVT
2 2
g/h·m 1.43 grains/h·ft
2 2
grains/h·ft 0.697 g/h·m
Permeance
2 7
g/Pa·s·m 1.75 × 10 1 Perm (Inch-pound)
D -8 2
1 Perm (Inch-pound) 5.72 × 10 g/Pa·s·m
Permeability
g/Pa·s·m 6.88 × 10 1 Perm-inch
-9
1 Perm-inch 1.45 × 10 g/Pa·s·m
A
These units are used in the construction trade. Other units may be used in other
standards.
B
All conversions of mm Hg to Pa are made at a temperature of 0 °C.
C
WVT = water vapor transmission.
D 2
1 Perm = 1 US Perm = 1 grains/h·ft ·in. Hg.
2. Referenced Documents
2.1 ASTM Standards:
C168 Terminology Relating to Thermal Insulation
C578 Specification for Rigid, Cellular Polystyrene Thermal Insulation
C1289 Specification for Faced Rigid Cellular Polyisocyanurate Thermal Insulation Board
D226/D226M Specification for Asphalt-Saturated Organic Felt Used in Roofing and Waterproofing
D779 Test Method for Determining the Water Vapor Resistance of Sheet Materials in Contact with Liquid Water by the Dry
Indicator Method
D1079 Terminology Relating to Roofing and Waterproofing
D1653 Test Methods for Water Vapor Transmission of Organic Coating Films
D3833/D3833M Test Method for Water Vapor Transmission of Pressure-Sensitive Tapes
E96/E96M Test Methods for Gravimetric Determination of Water Vapor Transmission Rate of Materials
E398 Test Method for Water Vapor Transmission Rate of Sheet Materials Using Dynamic Relative Humidity Measurement
E631 Terminology of Building Constructions
E2556/E2556M Specification for Vapor Permeable Flexible Sheet Water-Resistive Barriers Intended for Mechanical Attachment
E3054/E3054M Guide for Characterization and Use of Hygrothermal Models for Moisture Control Design in Building
Envelopes
F1249 Test Method for Water Vapor Transmission Rate Through Plastic Film and Sheeting Using a Modulated Infrared Sensor
2.2 ANSI/ASHRAE Standard:
ANSI/ASHRAE 160 Criteria for Moisture-Control Design Analysis in Buildings (ANSI Approved)
2.3 Other Informative References:
ICC-ES Acceptance Criteria AC38 Water-resistive Barriers
ICC-ES Acceptance Criteria AC71 Foam Plastic Sheathing Panels Used as Water-resistive Barriers
ICC-ES Acceptance Criteria AC212 Water-resistive Coatings Used as Water-resistive Barriers over Exterior Sheathing
ICC-ES Acceptance Criteria AC310 Water-resistive Membranes Factory-bonded to Wood-based Structural Sheathing, Used as
Water-resistive Barriers
5 5
IBC ICC International Building Code
5 5
IRC ICC International Residential Code
3. Terminology
3.1 Definitions—For possible variation in definitions of terms used in this guide, refer to corresponding Terminology section in
Terminologies C168, D1079, and E631.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Available from American Society of Heating, Refrigerating, and Air-Conditioning Engineers, Inc. (ASHRAE), 1791 Tullie Circle, NE, Atlanta, GA 30329,
http://www.ashrae.org.
Available from ICC Evaluation Service (a registered trademark) (ICC-ES), 3060 Saturn Street, Suite 100, Brea, Ca 92821, https://icc-es.org.
Available from and a registered trademark of International Code Council (ICC), 500 New Jersey Ave., NW, 6th Floor, Washington, DC 20001, http://www.iccsafe.org.
E3127 − 24
3.2 Definitions of Terms Specific to This Standard:
3.2.1 air barrier (AB), n—a material or assembly installed as a system in a building envelope and designed to resist uncontrolled
air movement into or through the opaque wall or roof assembly. An air barrier can be specified as a control layer on the inside,
outside, or middle sections of exterior wall and roof assemblies, or as an entire assembly.
3.2.1.1 Discussion—
A given material may serve multiple functions within a wall or roof assembly if it meets the requirements for each function. For
example, it is possible to specify and install a single product that functions both as a water-resistive and air barrier on the exterior
side of the assembly. Some products can also provide additional structural support and thermal insulating capability.
3.2.2 air leakage, n—in buildings, the passage of uncontrolled air through cracks or openings in the building envelope or its
components, such as ducts, because of air pressure or temperature difference.
3.2.3 building envelope, n—a boundary that encloses and separates conditioned space from the outdoor environment or other
environments with different conditions (for example, semi-conditioned spaces, cold storage spaces, manufacturing or industrial
processing environments).
3.2.3.1 Discussion—
A building’s interior is typically the enclosed conditioned space that, in general, does not include vented attics, unconditioned
basements, vented crawl spaces, or attached spaces (for example, unconditioned garages or other utility spaces that are connected
to the main structure but are not conditioned). In commercial buildings, these interior environments may include designated spaces
for storage, manufacturing, or industrial processing.
3.2.4 responsive water vapor transmission properties, n—water vapor transmission properties that vary as a function of
temperature and relative humidity.
3.2.4.1 Discussion—
The water vapor permeance (WVP) of many WRB/AB materials increases with increasing temperature and relative humidity, often
in a nonlinear fashion.
3.2.5 water vapor diffusion, n—the process by which water vapor moves through a vapor permeable material by molecular
diffusion due to a difference (gradient) in water vapor pressure across the material.
3.2.6 water-resistive barrier (WRB), n—a protective material installed on the exterior surface or behind the exterior building
covering (for example, wall cladding or roof covering) that is intended to resist further intrusion of liquid water that has penetrated
the exterior covering and prevent it from reaching interior components of the building envelope.
3.2.6.1 Discussion—
Wall and roof assemblies designed to function as a drainage system include two layers of resistance against rainwater penetration;
the exterior covering provides the initial resistance to rainwater penetration, and the WRB provides the ultimate resistance against
any water that bypasses the exterior covering or drains down from upper levels.
3.2.7 water vapor permeability, n—a material property that represents the time rate of water vapor transmission by diffusion
through unit area of a flat material of unit thickness induced by a unit vapor pressure difference between two specific surfaces,
under specified temperature and relative humidity conditions.
3.2.8 water vapor permeance, n—a material layer property that represents the time rate of water vapor transmission by diffusion
through unit area of a flat material or assembly induced by a unit vapor pressure difference between two specific surfaces, under
specified temperature and humidity conditions.
3.2.8.1 Discussion—
Permeance is an extrinsic material property for the specific thickness of the material. Permeability is an intrinsic material property
that must be divided by the thickness to determine the permeance of the material. Water vapor permeance has been traditionally
reported in “perms,” and material classes are established based on this perm rating for sheet- and fluid-applied materials.
3.2.9 water vapor transmission rate (WVTR), n—the steady water vapor flow by diffusion in unit time through unit area of a
material, normal to specific parallel surface, under specific temperature and relative humidity conditions on each surface.
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3.2.9.1 Discussion—
Water vapor transmission rate is sometimes reported as the amount of water vapor flow over a 24 h time interval, for example,
2 2
g/24 h·m or grains/24 h·ft . It is required that the units are reported with the numerical value when stating the WVTR or water
vapor permeance of a material.
3.2.9.2 Discussion—
Although some technical documents report WVTR values as a measure of water vapor permeance of building materials instead
of traditionally reported “perm” rating, the WVTR is not a complete performance measure of water vapor transmission. If water
vapor pressure differentials across tested specimens are not reported, estimation of water vapor transmission properties cannot be
accomplished without making assumptions about the water vapor pressures on each side of tested specimens.
3.3 Symbols:
2 2
q = mass flux rate of vapor flow, grains/h·ft , (kg/s·m )
v
μ = water vapor permeability, grains/h·ft·in. Hg, (kg/Pa·s·m)
p
2 2
M = water vapor permeance, grains/h·ft ·in. Hg, (kg/Pa·s·m )
P = water vapor pressure, in. Hg (Pa)
v
P = saturation water vapor pressure, in. Hg, (Pa)
v,sat
2 2
WVTR = water vapor transmission rate, grains/h·ft , (g/h·m )
4. Significance and Use
4.1 As the building industry shifts towards performance-based design, specification of material properties consistent with
anticipated in-service conditions becomes paramount to the design process. When specifying water vapor transmission properties,
it is important to identify water vapor transmission properties for WRB/AB products that are measured under test conditions
relevant to anticipated in-service conditions. This guide provides a performance-based framework for characterizing the water
vapor transmission properties of WRB/AB.
4.2 When specifying WRB/AB, water vapor permeance is an important attribute to consider for proper moisture management and
functioning of wall and roof assemblies in service. In North America, water vapor transmission properties of water-resistive and
air barrier materials are traditionally tested in accordance with Test Methods E96/E96M. This guide adopts the ASTM E96/E96M
test methods as a primary source of information for water vapor transmission properties of WRB/AB unless otherwise instructed
by the design professional.
4.3 Most standard test methods rely on a limited set of steady-state testing conditions for evaluating the water vapor transmission
properties of materials. Test conditions used to measure and report water vapor transmission values of WRB/AB should represent
the in-service conditions of the tested material as closely as possible (that is, should cover the range of temperature and relative
humidity conditions the products will experience when installed in wall and roof assemblies). The water vapor permeance of many
WRB/AB materials can vary by more than an order of magnitude when tested for ranges of temperatures and relative humidity
expected in service. For this reason, WVT properties over the full range of environmental conditions that the material will most
likely experience in service should be used or evaluated when specifying a material or assembly design for a specific project.
5. Classification
5.1 This guide addresses selection and reporting of water vapor transmission properties for WRB/AB in accordance with their
in-service conditions regardless of the manufacturing process and physical characteristics of the products.
5.2 The International Building Code (IBC) and International Residential Code (IRC) adopt the following vapor retarder classes
for materials as defined using the Desiccant Method (“Procedure A”) of Test Methods E96/E96M:
(1) Class I: 0.1 perm or less,
(2) Class II: 0.1 < perm ≤ 1.0 perm, and
(3) Class III: 1.0 < perm ≤ 10 perm.
The vapor retarder classes listed above have been primarily developed for classification of vapor retarders installed typically on
the interior side of frame walls to better characterize potential of vapor retarders to control the magnitude of water vapor diffusion
from inside to outside in winter time. The vapor retarder classes in 5.2 may not be sufficient to provide complete metrics needed
to characterize the performance of WRB/AB.
5.2.1 For proper characterization of water vapor retarding properties for WRB/AB in service, selected test methods and test
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conditions should reproduce the full range of temperatures and relative humidity encountered in service. It is strongly
recommended that technical data sheets for WRB/AB report water vapor transmission properties for at least three mean relative
humidity levels:
(1) 25 % (matches the Desiccant Method or Procedure “A” test conditions in accordance with Test Methods E96/E96M),
(2) 75 % (matches the Water Method or Procedure “B” test conditions in accordance with Test Methods E96/E96M), and
(3) 95 % (evaluates performance in “wet” conditions and assesses potential for drying after incidental water intrusion events).
5.2.1.1 The reported values for each recommended average relative humidity level should be assessed at three different
temperatures covering the most typical range of temperatures expected in service: 40 °F, 73.4 °F, and 90 °F.
5.2.1.2 It is recommended that test results be presented in graphical form by using a water vapor permeance performance chart
as shown in Fig. 1, which provides a summary of test data for three different products “A,” “B,” and “C” represented by green,
blue, and red boxes, respectively. Numeric labels next to the green boxes indicate mean relative humidity for each tested
temperature, and width of the boxes corresponds to tested permeance values to be reported. For clarity, relative humidity labels
were omitted for products “B” and “C.” It is possible that certain WRB/AB products demonstrate a wider range of water vapor
permeance values at different humidity and temperature conditions than others.
5.2.2 The Desiccant Method (“Procedure A”) of ASTM E96/E96M test methods is conducted at a single environmental condition,
73 °F (23 °C) and average relative humidity (RH) of 25 % and may be used as a baseline to characterize vapor retarding properties
for WRB/AB.
5.2.3 In addition to the Desiccant Method (“Procedure A”), Test Methods E96/E96M specifiesspecify five other standard test
conditions and permits the use of additional temperature and RH conditions with the requirement that test conditions shall be stated
in the test report.
6. Test Methods and Practices
6.1 Regardless of the test method used for evaluation of water vapor transmission properties of WRB/AB, it is highly
recommended that selected test conditions represent the anticipated range of in-service conditions.
6.2 ASTM Test Methods E96/E96M isare recommended as a primary test method for determining the WVT properties of both
WRB/AB, unless the nature of the tested material, test method conditions, or the range and dynamics of in-service conditions
suggest an alternative test method would be more appropriate.
NOTE 1—Perm ratings on top of the chart expressed in US perms on logarithmic scale.
FIG. 1 Proposed WVP Performance Chart for WRB/AB
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6.3 Test Methods E96/E96M provide a limited number of recommended standard test conditions (temperature and relative
humidity). The test chamber conditions for the two most widely reported test methods, Desiccant Method (“Procedure A”) and
Water Method (“Procedure B”), are 73.4 °F (23 °C) and 50 % 6 2 % relative humidity. The test dishes are filled either with dried
desiccant to maintain 0 % relative humidity (“Procedure A”), or with distilled water (“Procedure B”) to maintain 100 % relative
humidity on one side of the tested material. These standard conditions, however, provide only limited information and may not
reflect the actual conditions that tested barrier materials may experience in service.
6.4 It is strongly recommended that, at a minimum, manufacturers of WRB/AB materials report the results for at least the two most
common test methods used in industry; that is, to test the material to both the ASTM Test Methods E96/E96M Desiccant Method
(“Procedure A”) and Water Method (“Procedure B”) to facilitate better the specification of water vapor transmission properties
based on project-specific conditions.
6.5 Test Methods E96/E96M isare a simple, straightforward, and relatively inexpensive testing protocol commonly used in the
industry to evaluate water vapor transmission properties of building materials. Variations in test results typically occur due to
inhomogeneity of tested material, fluctuations in environmental conditions, a lack of detailed specifications for shape and size of
test dishes, absence of detailed instructions for sealing methods, reliance on operator skill to adequately seal the test specimen, and
difficulties in test specimen preparation for certain categories of WRB/AB products. Typically, these test methods provide reliable
and repeatable values for water vapor transmission properties of building materials by means of simple apparatus; however,
interlaboratory studies conducted on several materials revealed that percent coefficient of variation could be up to 20 % for some
materials as reported in Precision and Bias section of the ASTM E96/E96M test standard.
6.6 Test reports should follow the Test Methods E96/E96M reporting requirements and include the test procedure or method, or
both, along with test temperature and relative humidity in the test chamber. If non-standard test conditions are selected, report
temperature and relative humidity on each side of the tested specimen. When testing multilayered and composite materials, report
the specimen side that was exposed to the environment with higher water vapor pressure and higher relative humidity, keeping in
mind that orientation may change with selected procedure (Desiccant Method versus Water Method).
6.7 Water vapor transmission properties obtained in accordance with alternative test methods such as ASTM Test Methods E398,
D1653, D3833/D3833M, or F1249 are also acceptable provided that reported water vapor transmission properties reflect in-service
conditions of the tested materials or conditions similar to “Procedure A” and “Procedure B” of ASTM E96/E96M test methods.
The test results generated using alternative test methods may not be equal to the test results produced using Test Methods
E96/E96M testing protocol for the same testing conditions. It is the design professional’s responsibility to interpret and use the
alternative test data accordingly in the design process. Some alternative test methods for measuring water vapor transmission allow
for material property testing under dynamic conditions. Test data generated under such conditions may be preferable when tested
materials will be subjected to similar conditions in service.
6.7.1 The benefits of using alternative test methods over Test Methods E96/E96M may include speed and ease in specifying of
variable test conditions. A limitation of some alternative test methods is the allowable specimen thickness that can be tested. As
most alternative test methods are designed for sheet and membrane materials, they may not be suitable for testing thick WRB/AB
products or composite materials.
6.8 Evaluation of interaction between barrier material and the exterior sheathing substrate and assessing the actual or effective
permeability is critical for performance assessment of barrier products that require full adhesion to the substrate (for example,
self-adhered membranes, fluid-applied, factory-laminated, or bonded products). Due to limitations imposed on specimen thickness,
use of certain test methods for evaluation of interaction between barrier material and exterior sheathing substrate may not be
appropriate.
6.9 In general, most standard test methods specify a limited set of conditions for evaluating the water vapor transmission
characteristics of tested material, and selection of alternative test methods, along with evaluation of reported test results using
alternative test methods, requires professional expertise and assessment.
7. In-Service Conditions and Water Vapor Permeance Reporting Requirements for Water-Resistive Barriers and Air
Barriers
7.1 In-service conditions impact the performance of WRB/AB and should be carefully considered when selecting conditions for
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measuring, reporting, and specifying water vapor transmission properties of barrier products for project-specific in-service
conditions. Factors governing the in-service conditions of WRB/AB as installed on the exterior side of building envelopes include,
but are not limited to:
(1) localLocal climate (for example, temperature, relative humidity, solar radiation, wind direction and wind speed,
precipitation);
(2) exposureExposure to liquid water in service (for example, cladding type and installation method, local site and building
exposure conditions such as wall orientation in relation to predominant wind-driven rain direction, location relative to protective
features such as overhangs and porches, and flashing practices employed for redirecting water);
(3) exposureExposure to indirect and intermittent ultraviolet (UV) radiation from sunlight in open joint rainscreen applications;
(4) interiorInterior ambient conditions (temperature and relative humidity);
(5) locationLocation of barrier material within the wall and roof assembly;
(6) characteristicsCharacteristics of other layers in the wall and roof assembly with regards to heat, air, and moisture transport
(for example, water vapor transmission and air leakage properties, moisture absorption, moisture storage characteristics, and
thermal insulating properties), as they all affect wetting and drying potential of a particular assembly; and
(7) propertiesProperties of the substrate to which the barrier is applied, and interaction between barrier, substrate material, and
flashing for proper installation (for example, chemical compatibility and use of adhesives, primers, and other means to adhere the
barrier material to the substrate and flashing).
7.1.1 Most severe wind-driven rain conditions, magnitude of water vapor drive, and corresponding thermal gradients throughout
the year in relation to moisture storage capacities and water vapor transmission properties of adjacent layers should be carefully
considered in selecting and reporting water vapor transmission characteristics of WRB (1). These factors can impact product
in-service performance due to variation in water vapor transmission characteristics with change in relative humidity and
temperature. Therefore, using test conditions that are consistent with the in-service environment of the barrier product is necessary
when providing water vapor transmission data to support the specification process.
7.2 Some WRB/AB products rely on either mechanical attachment or physical bonding (for example, fluid-applied and
self-adhered products) to the substrate for proper installation; others are manufactured with the WRB/AB laminated directly to the
exterior sheathing. Physical interaction between the barrier material and the substrate can affect the water vapor transmission
characteristics of multilayered composites. To achieve a minimum required bond strength to a particular substrate, some WRB/AB
products specify the use of primers, which also may affect the water vapor transmission characteristics of the composite product.
Therefore, in addition to evaluating the water vapor transmission characteristics of individual layers in a multilayered system,
evaluation of the water vapor transmission properties of composite products that include substrate, surface treatments, and coatings
or facers is recommended.
7.3 Water vapor permeability measured under test conditions representative of the in-service conditions should be used when
choosing a material for a particular building application (2).
7.3.1 For WRB/AB materials with vapor transmission properties not significantly impacted by changes in temperature and relative
humidity, specifying testing conditions and reporting water vapor transmission properties in accordance with in-service conditions
is less relevant.
7.3.2 For WRB/AB materials with responsive water vapor transmission characteristics, that is, water vapor transmission properties
that vary with temperature and relative humidity, it is essential to select and report the water vapor transmission values measured
under conditions that are similar to expected in-service conditions. The specification and reporting documents for these products
should acknowledge that variability can exist in water vapor transmission properties and take fluctuating in-service conditions into
consideration. It is recommended to report test results in graphic form that reflect a range of varying hygrothermal conditions
representative of in-service conditions (3), and reporting metrics as described in 5.2.1 should be used. Though the limited set of
testing conditions does not fully represent actual conditions these materials may encounter in service, testing to these standard test
conditions provides adequate performance metrics for comparison of water vapor transmission material properties of water-
resistive and air barriers.
7.4 It is the design professional’s responsibility to select and specify The selection and specification of the water vapor
permeability and water vapor permeance values transmission properties for WRB/AB appropriate for the given application.
application should be included in the design process. Ideally, the WVT characteristics should be defined across the whole range
of relative humidity and temperature values expected in service. Complete evaluation of water vapor transmission characteristics
The boldface numbers in parentheses refer to the list of references at the end of this standard.
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for WRB/AB can be time consuming, and current industry standards do not prescribe such comprehensive test condition
requirements for these barrier products. The intent of the subsequent sections
...