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 MIL-HDBK-1001/5A
d)
Vapor retarder (if required);
e)
Membrane coating (refer to par. 7.3.3);
f) Fire resistance ratings. Class A when tested by UL
790, Tests for Fire Resistance of Roof Covering Materials and FM
Class 1 for most applications;
g)
Flashing details.
7.3.1
Foam Thickness and Slope. Whenever possible, slope the
deck rather than varying foam thickness to provide surface slope.
Slope may also be provided by installation of compatible, tapered
roof insulation as a substrate before spray application of
uniformly thick foam. Uniform thickness is more apt to produce
uniform quality because varying thickness requires varying spray
rate to maintain uniform chemical reaction rate. If slope is
provided by foam, use tapered boards to indicate proper surface
contours of foam.
7.3.2
Control Joints. Provide control joints at all re-entry
corners, with roof divided into sections of 10,000 square feet
(929 square meters) or less.
7.3.3
Membrane Coatings. Polyurethane foam requires a
protective membrane covering. A good membrane coating must have
these properties:
a)
Good adhesion;
b) Temperature stability (i.e., viscous at high
temperature, but not brittle at low temperature);
c)
Abrasion resistance;
d)
Weather resistance (to solar radiation, rain);
e) Maintainability (ease of repair when damaged,
integration of repaired section with original material);
f)
Durability;
g)
Strength and elasticity;
h)
Low permeability in humid climates.
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