ASTM C755-20
(Practice)Standard Practice for Selection of Water Vapor Retarders for Thermal Insulation
Standard Practice for Selection of Water Vapor Retarders for Thermal Insulation
SIGNIFICANCE AND USE
4.1 Experience has shown that uncontrolled water entry into thermal insulation is the most serious factor causing impaired performance. Several ways exist by which water enters into an insulation system, the primary ones being diffusion of water vapor, air leakage carrying water vapor, and leakage of surface water. Application specifications for insulation systems that operate below ambient dew-point temperatures necessarily include an adequate vapor retarder system. A vapor retarder system is separate and distinct from the insulation, or is provided by the insulation itself when it is has adequate vapor resistant properties and all joints are sealed against water vapor intrusion, in which case a separate vapor retarder system is not necessary. For selection of adequate retarder systems to control vapor diffusion, it is necessary to establish acceptable practices and standards.
4.2 Vapor Retarder Function—The primary function of a vapor retarder is to control movement of diffusing water vapor into or through a permeable insulation system. The vapor retarder system in some cases is designed to prevent entry of surface water. When properly functioning as a vapor retarder, it will also serve as a barrier to air leakage.
4.3 Vapor Retarder Performance—Design choice of retarders will be affected by thickness of retarder materials, substrate to which applied, the number of joints, available length and width of sheet materials, useful life of the system, and inspection procedures. Each of these factors will have an effect on the retarder system performance and each must be considered and evaluated by the designer.
4.3.1 Although this practice properly places major emphasis on selecting the best vapor retarders, it must be recognized that faulty installation is likely to impair vapor retarder performance. The effectiveness of installation or application techniques in obtaining design water vapor permeance (WVP) performance must be considered in the selection of ret...
SCOPE
1.1 This practice outlines factors to be considered, describes design principles and procedures for water vapor retarder selection, and defines water vapor transmission values appropriate for established criteria. It is intended for the guidance of design engineers in preparing vapor retarder application specifications for control of water vapor flow through thermal insulation. It covers commercial and residential building construction and industrial applications in the service temperature range from −40 to +150°F (−40 to +66°C). Emphasis is placed on the control of moisture penetration by choice of the most suitable components of the system.
1.2 The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical conversions to SI units that are provided for information only and are not considered standard.
1.3 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.
1.4 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.
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Standards Content (Sample)
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.
Designation: C755 − 20
Standard Practice for
1
Selection of Water Vapor Retarders for Thermal Insulation
This standard is issued under the fixed designation C755; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope C921Practice for Determining the Properties of Jacketing
Materials for Thermal Insulation
1.1 Thispracticeoutlinesfactorstobeconsidered,describes
C1136Specification for Flexible, Low Permeance Vapor
design principles and procedures for water vapor retarder
Retarders for Thermal Insulation
selection, and defines water vapor transmission values appro-
E96/E96MTest Methods for Water Vapor Transmission of
priate for established criteria. It is intended for the guidance of
Materials
design engineers in preparing vapor retarder application speci-
fications for control of water vapor flow through thermal
3. Terminology
insulation. It covers commercial and residential building con-
struction and industrial applications in the service temperature
3.1 For definitions of terms used in this practice, refer to
range from−40 to+150°F (−40 to+66°C). Emphasis is placed
Terminology C168.
on the control of moisture penetration by choice of the most
suitable components of the system.
4. Significance and Use
1.2 The values stated in inch-pound units are to be regarded
4.1 Experiencehasshownthatuncontrolledwaterentryinto
as standard. The values given in parentheses are mathematical
thermal insulation is the most serious factor causing impaired
conversions to SI units that are provided for information only
performance. Several ways exist by which water enters into an
and are not considered standard.
insulation system, the primary ones being diffusion of water
1.3 This standard does not purport to address all of the
vapor, air leakage carrying water vapor, and leakage of surface
safety concerns, if any, associated with its use. It is the
water. Application specifications for insulation systems that
responsibility of the user of this standard to establish appro-
operate below ambient dew-point temperatures necessarily
priate safety, health, and environmental practices and deter-
include an adequate vapor retarder system. A vapor retarder
mine the applicability of regulatory limitations prior to use.
system is separate and distinct from the insulation, or is
1.4 This international standard was developed in accor-
provided by the insulation itself when it is has adequate vapor
dance with internationally recognized principles on standard-
resistantpropertiesandalljointsaresealedagainstwatervapor
ization established in the Decision on Principles for the
intrusion, in which case a separate vapor retarder system is not
Development of International Standards, Guides and Recom-
necessary.Forselectionofadequateretardersystemstocontrol
mendations issued by the World Trade Organization Technical
vapordiffusion,itisnecessarytoestablishacceptablepractices
Barriers to Trade (TBT) Committee.
and standards.
4.2 Vapor Retarder Function—The primary function of a
2. Referenced Documents
vapor retarder is to control movement of diffusing water vapor
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2.1 ASTM Standards:
into or through a permeable insulation system. The vapor
C168Terminology Relating to Thermal Insulation
retarder system in some cases is designed to prevent entry of
C647Guide to Properties and Tests of Mastics and Coating
surface water. When properly functioning as a vapor retarder,
Finishes for Thermal Insulation
it will also serve as a barrier to air leakage.
4.3 Vapor Retarder Performance—Design choice of retard-
1
erswillbeaffectedbythicknessofretardermaterials,substrate
This practice is under the jurisdiction of ASTM Committee C16 on Thermal
Insulation and is the direct responsibility of Subcommittee C16.33 on Insulation
to which applied, the number of joints, available length and
Finishes and Moisture.
width of sheet materials, useful life of the system, and
Current edition approved March 1, 2020. Published March 2020. Originally
inspectionprocedures.Eachofthesefactorswillhaveaneffect
approved in 1973. Last previous edition approved in 2019 as C755–19b. DOI:
10.1520/C0755-20. on the retarder system performance and each must be consid-
2
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
ered and evaluated by the designer.
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
4.3.1 Althoughthispracticeproperlyplacesmajoremphasis
Standards volume information, refer to
...
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: C755 − 19b C755 − 20
Standard Practice for
1
Selection of Water Vapor Retarders for Thermal Insulation
This standard is issued under the fixed designation C755; 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 practice outlines factors to be considered, describes design principles and procedures for water vapor retarder selection,
and defines water vapor transmission values appropriate for established criteria. It is intended for the guidance of design engineers
in preparing vapor retarder application specifications for control of water vapor flow through thermal insulation. It covers
commercial and residential building construction and industrial applications in the service temperature range from −40 to +150°F
(−40 to +66°C). Emphasis is placed on the control of moisture penetration by choice of the most suitable components of the
system.
1.2 The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical
conversions to SI units that are provided for information only and are not considered standard.
1.3 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.
1.4 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.
2. Referenced Documents
2
2.1 ASTM Standards:
C168 Terminology Relating to Thermal Insulation
C647 Guide to Properties and Tests of Mastics and Coating Finishes for Thermal Insulation
C921 Practice for Determining the Properties of Jacketing Materials for Thermal Insulation
C1136 Specification for Flexible, Low Permeance Vapor Retarders for Thermal Insulation
E96/E96M Test Methods for Water Vapor Transmission of Materials
3. Terminology
3.1 For definitions of terms used in this practice, refer to Terminology C168.
4. Significance and Use
4.1 Experience has shown that uncontrolled water entry into thermal insulation is the most serious factor causing impaired
performance. Several ways exist by which water enters into an insulation system, the primary ones being diffusion of water vapor,
air leakage carrying water vapor, and leakage of surface water. Application specifications for insulation systems that operate below
ambient dew-point temperatures necessarily include an adequate vapor retarder system. A vapor retarder system is separate and
distinct from the insulation itself, insulation, or is provided by the insulation itself when it is has adequate vapor resistant properties
and all joints are properly sealed against water vapor intrusion, in which case a separate vapor retarder system is not necessary.
For selection of adequate retarder systems to control vapor diffusion, it is necessary to establish acceptable practices and standards.
4.2 Vapor Retarder Function—The primary function of a vapor retarder is to control movement of diffusing water vapor into
or through a permeable insulation system. The vapor retarder system in some cases is designed to prevent entry of surface water.
When properly functioning as a vapor retarder, it will also serve as a barrier to air leakage.
1
This practice is under the jurisdiction of ASTM Committee C16 on Thermal Insulation and is the direct responsibility of Subcommittee C16.33 on Insulation Finishes
and Moisture.
Current edition approved Oct. 15, 2019March 1, 2020. Published November 2019March 2020. Originally approved in 1973. Last previous edition approved in 2019 as
C755 – 19a.C755 – 19b. DOI: 10.1520/C0755-19B.10.1520/C0755-20.
2
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.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
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