ASTM C755-97
(Practice)Standard Practice for Selection of Vapor Retarders for Thermal Insulation
Standard Practice for Selection of Vapor Retarders for Thermal Insulation
SCOPE
1.1 This practice outlines factors to be considered, describes design principles and procedures for 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 temperature range from -40 to +80°F (-40 to +27°C) within the structure. Emphasis is placed on the control of moisture penetration by choice of the most suitable components of the system.
1.2 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 and health practices and determine the applicability of regulatory limitations prior to use.
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Designation: C 755 – 97
AMERICAN SOCIETY FOR TESTING AND MATERIALS
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Reprinted from the Annual Book of ASTM Standards. Copyright ASTM
Standard Practice for
1
Selection of Vapor Retarders for Thermal Insulation
This standard is issued under the fixed designation C 755; 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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope which a specific atmosphere is saturated with water vapor.
(Cooling below the dew point will cause release of water vapor
1.1 This practice outlines factors to be considered, describes
in the form of condensation. In problem analysis for vapor
design principles and procedures for vapor retarder selection,
barrier selection it is the dew-point temperature, not the
and defines water vapor transmission values appropriate for
relative humidity, that is pertinent. Dew-point temperature is
established criteria. It is intended for the guidance of design
directly related to saturation water vapor pressure and may be
engineers in preparing vapor retarder application specifications
obtained from tables.)
for control of water vapor flow through thermal insulation. It
3.1.2 thermal insulation system, n—thermal insulation for
covers commercial and residential building construction and
resistance to heat flow combined with means for attachment to
industrial applications in the temperature range from − 40
the surface to be insulated, and with facings, vapor retarders,
to + 80°F (−40 to + 27°C) within the structure. Emphasis is
joint sealants, or protective coatings as installed.
placed on the control of moisture penetration by choice of the
3.1.3 vapor retarders, n—those materials or systems which
most suitable components of the system.
adequately retard the transmission of water vapor under
1.2 This standard does not purport to address all of the
specified conditions. (For practical purposes it is assumed that
safety concerns, if any, associated with its use. It is the
the permeance of an adequate retarder will not exceed 1 perm,
responsibility of the user of this standard to establish appro-
although at present this value may be adequate only for
priate safety and health practices and determine the applica-
2
residential construction. For certain other types of construction
bility of regulatory limitations prior to use.
the permeance must be very low.)
2. Referenced Documents
3.1.4 water vapor diffusion, n—the process by which water
vapor spreads or moves through permeable materials caused by
2.1 ASTM Standards:
a difference in water vapor pressure.
D 828 Test Method for Tensile Properties of Paper and
3.1.5 water vapor permeability (permeability), n—the water
Paperboard Using Constant-Rate-of-Elongation Appara-
3
vapor transmission of a homogeneous material under unit
tus
vapor pressure difference between two specific surfaces, per
E 84 Test Method for Surface Burning Characteristics of
4
unit thickness. An acceptable unit of permeability is the
Building Materials
2
perm-inch: grain-in./h·ft ·in. Hg (the metric perm-cm 5 1
E 96 Test Methods for Water Vapor Transmission of Mate-
2
5
g·cm/24 h·m ·mm Hg).
rials
3.1.6 water vapor permeance (permeance), n—the water
F 372 Test Method for Water Vapor Rate Transmission of
vapor transmission of a material under unit vapor pressure
Flexible Barrier Materials Using an Infrared Detection
3
difference between two specific surfaces. An acceptable unit of
Technique
2
permeance is the perm: grain/h·ft in. Hg (1 metric perm 5 1
2.2 TAPPI Standard:
2
6
g/24 h·m mm Hg).
T803, Puncture Test of Containerboard
3.1.7 water vapor transmission (WVT), n—the steady-state
3. Terminology
time rate of water vapor diffusion or flow through unit area of
a material, normal to specific parallel surfaces under specific
3.1 Definitions:
conditions of temperature and humidity at each surface. An
3.1.1 dew-point temperature (Dp), n—the temperature at
2 2
acceptable unit of WVT is grain/h·ft (1 g/24 h·m ).
1
This practice is under the jurisdiction of ASTM Committee C-16 on Thermal
4. Significance and Use
Insulation and is the direct responsibility of Subcommittee C16.33 on Thermal
Insulation Finishes and Vapor Transmission. 4.1 Experience has shown that uncontrolled water entry into
Current edition approved May 10, 1997. Published August 1997. Originally
thermal insulation is the most serious factor causing impaired
published as C 755 – 73. Last previous edition C 755 – 85 (1990).
performance. Water entry into an insulation system may be
2
Discontinued; see 1983 Annual Book of ASTM Standards, Vol 15.09.
3
through diffusion of water vapor,
...
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