2.11
VAPOR RETARDER
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NOTE: The term vapor retarder has been selected to
describe the membrane used to reduce moisture vapor
transmission. The location of the vapor retarder is
determined by the climate and the building type.
The vapor retarder goes on the side of the
insulation with the greatest vapor pressure during
the course of the year; therefore, it goes on the
outside in a climate predominately warm, and on the
inside in a climate predominately cool. The
designer should determine the most appropriate
application/installation of the vapor retarder based
on project circumstances and the intended use of the
facility. See TM 5-810-1 for humid climate
definition.
Detail the use of insulation on the drawings.
The
four systems are as follows:
a. Cool climate, no roof deck. The vapor retarder
will be a facing on the bottom of blanket insulation.
b. Warm climate, no roof deck. The vapor retarder
will be a facing on the top of blanket insulation
with a separate insulation support system. A slip
sheet is required. If the integral facing is used
to support the insulation, a separate polyethylene
vapor retarder must be laid over the insulation.
c. Cool climate, with a roof deck. The vapor
retarder will be a separate membrane directly on top
of the roof deck with board insulation over the
vapor retarder and an unfaced blanket cushioning
between the board insulation and the roofing.
d. Warm climate, with a roof deck. The vapor
retarder will be a facing on the top of a blanket
insulation above board insulation. The board
insulation sits on the roof deck. A slip sheet is
required.
Unreinforced foil as the facing in conditions b. and
d. above, should not be used.
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2.11.1
Vapor Retarders as Integral Facing
Insulation facing shall have a permeability of [1.15] [_____] ng per
Pa-second-square meter [0.02] [_____] perm or less when tested in
accordance with ASTM E 96. Facing shall be [white] [black] reinforced
polypropylene kraft laminate (PSK). Facings and finishes shall be factory
applied.
2.11.2
Vapor Retarders Separate from Insulation
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SECTION 07416A
Page 24
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