MIL-HDBK-1011/1
7.8.2
Aluminum. Aluminum roofing is 18 gauge minimum and anodized
(0.7 mil)
or otherwise factory coated both sides. Separate the aluminum from
the steel
framework by applying a bituminous coating to either the aluminum or
the steel
at the bearing points. Use stainless steel fasteners.
7.9
Insulation and Vapor Barrier. Give special consideration to
particularly high humidity locales such as Guam, Philippines, and Diego Garcia
where the 1 percent outdoor ambient dewpoint temperatures in excess of 70
degrees F may be higher than the design indoor dry bulb temperature. Where
this situation exists, select the insulation to maintain its exterior surface
temperatures above the ambient dewpoint temperature. Install a continuous
vapor barrier at a location where its temperature will be above the ambient
dew-point temperature to prevent water vapor from infiltrating and condensing
within the walls.
(See Figures 2 and 3.)
7.9.1
Foam Glass. Foam glass rigid insulation board is a good insulating
material with a high heat resistance (R) value, is dense enough for foot
traffic, and will not absorb water. Foam glass is expensive, however, and is
therefore not often used as a roof insulation.
7.9.2
Fiberglass.
Fiberglass insulation is often used as a topside
insulation under a built-up roofing membrane. This insulation will readily
absorb, conduct, and hold water and is therefore often the cause of a roofing
failure. On the other hand, fiberglass is a very good insulating material
when placed inside the building on top of a suspended ceiling. Fiberglass is
not recommended as a topside insulation.
Figure 2
Moisture Migration and Dew Point
35
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