roofing problem resulting from water-vapor
infiltration.
Delete contractor's option for single-layer vapor
retarder for roofs over areas having excessively
high interior humidity such as swimming pools and
laundries. Generally, vapor retarder should be in
direct contact with deck. However, compute dewpoint
temperature and location and locate vapor retarder
below dewpoint location. Avoid use of vapor
retarder over steel decks unless vapor retarder is
determined to be absolutely necessary. Do not
specify wood fiberboard or any type of insulation
that is highly sensitive to moisture for layer
directly on steel deck. Specify installation of
insulation over vapor retarder using hot asphalt to
avoid puncturing vapor retarder. Combination of two
or more layers of insulation should be of such
thickness that dewpoint temperature will occur above
vapor retarder located directly over first layer of
insulation. Topside venting should always be
provided by insulation vents and perimeter edge
vents when vapor retarder is used. Specify venting
requirements in roofing membrane specification
section.
Unless otherwise directed, do not specify vapor
retarder for projects in the SOUTHNAVFACENGCOM area.
**************************************************************************
[2.5.1
Vapor Retarder]
[2.5.1.1
Asphalt-Saturated Felt Base Sheet for Single Layer Application
ASTM D 4601, weighing not less than 17.5 kilograms per 10 square meters 35
pounds per 100 square feet.]
[2.5.1.2
Asphalt-Coated Glass Felt
ASTM D 2178, Type [IV] [VI].]
[2.5.2
Ventilating Felt for [Poured] [Precast] Concrete Decks
**************************************************************************
NOTE: Specify ventilating felt for new and existing
concrete decks suspected of having retained moisture
to aid in dissipation of any moisture retained in
concrete. This felt shall not be considered to be a
vapor retarder.
**************************************************************************
ASTM D 4897, Type II, non-perforated, with spot mopping holes where
specified.]
2.5.3
Organic Roofing
ASTM D 226, Type I.
SECTION 07220
Page 16
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