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 MIL-HDBK-1001/5A
Section 8: PROTECTED MEMBRANE ROOF SYSTEM
8.1
Description. The protected membrane roof system (PMR),
also known as the "IRMA" roof, or inverted roof membrane
assembly, reverses the positions of membrane and insulation in
the conventional built-up membrane roofing system. Instead of
its conventional exposed position atop the insulation, a PMR
membrane is sandwiched between the insulation above and the deck
below. A PMR, from bottom up, may include the following
components:
a)
Deck;
b)
Suitable underlayment leveling board (steel decks
only);
c) Additional layer of insulation (optional; for
energy savings; may be tapered to improve slope to drain);
d)
Membrane;
e)
Percolation course (optional);
f)
Insulation;
g)
Filter fabric;
h)
Ballast (aggregate or pavers).
8.2
General Design Recommendations
8.2.1
Structural Capacity. First consider the structure's
load-carrying capacity. There must be structural capacity to
carry the additional ballast or paver dead load required by this
system.
8.2.2
Slope. Slope deck and membrane a minimum 1/2 inch per
foot (4 percent) for new construction.
8.2.3
Water-Test. When practical, require that roofer water-
test completed membrane before installing insulation and
surfacing with special attention to expansion joints and
flashings. Leaks generally occur under expansion joints,
flashings, and at embedded edge metal.
8.2.4
Climate. PMR's are well-suited to cold climates, as
the membrane doubles as a vapor retarder. The best location for
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