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missiles. SPF roofs performed well in hurricane Andrew, especially when they were spray-applied
directly to concrete roof decks.
(9) Resistance to Ponding Water. Membrane roof systems rely upon sealed seams to
resist hydrostatic pressure. Water absorption may result in root or algae growth or cause rot. H
infers highly resistant to these conditions.
(10) Traffic Wear Resistance. Roofs that have a lot of rooftop equipment will have foot
traffic that can cause punctures or abrasion. Most roof systems are available with traffic protective
overlayers, such as walkways. H indicates highly resistant to abuse assuming protective courses
have been used.
(11) Resistance to Chemicals (resistance to oils, fats, grease, metal ions). Some roof
surfaces are vulnerable to exhausted fumes or liquids. Thermoplastic polyolefins (TPO's) and
Hypalon (CSPE) may be better than bituminous materials in resistance to oils, greases, and
solvents. Copper-containing runoff water from condensate coils or flashings will corrode zinc and
zinc-aluminum SSSMR roofing. H indicates better than average resistance to attack.
c. Weight Factor. Consider the total number of roofs already installed, the weight of the
proposed roof system possible, and construction loads. The unit weight of membrane systems
vary dramatically, ranging from less than 2.4 kg/sq. m (0.5 psf) for a 50 mm (2 in.) thickness of
SPF, to more than 100 kg/sq. m (20 psf) for ballasted single-ply systems. Typical roof system
weights and construction loads are shown in Table 2-6.
d. Compliance with Fire & Wind Requirements. Roofing systems are rated as entire
systems, including the roof deck, method of attachment to the deck (e.g., fasteners, hot bitumen,
cold adhesives), vapor retarder (if used), thermal insulation, roof membrane, and surfacing.
Typical External Fire Ratings (ASTM E-108, Class A, B or C) are shown in Tables 2-7 and 2-8.
Combustible decks (wood/plywood/OSB) require selected combinations of underlayments,
insulation, roofing, and surfacing to resist burning brands and intermittent flame as described in
ASTM E108. (See Additional discussion in 10.h. Fire Considerations.) Also refer to MIL
e. Roof Decking. Principle roof decks for membrane roofing include steel, cast-in-place
concrete, precast concrete, wood, plywood, OSB, and structural wood fiber. Variations of cast-in-
place concrete include lightweight structural concrete (typically 1680 kg/m )(105 psf) and
lightweight insulating concrete(480 kg/m3)(30 psf). In new design, the roof deck is generally
selected based upon construction considerations and materials. Steel is by far the most popular,
followed by concrete and plywood/OSB. Table 2-9 lists some criteria for deck selection for new
construction. Table 2-9 lists methods of attachment to the roof deck. Attachment options include
full adhesion, mechanical fastening, and loose-laid/ballasted roofing. Steel decking requires a
bridging course typically mechanically fastened roof insulation. For steep roofing, plywood and
OSB roof decks are most common. They generally utilize flexible batts as underdeck roof
insulation although architectural metal and cathedral ceiling constructions may use rigid insulation
above the deck.
f. Suitability of the Membrane for the Substrate. Table 2-10 lists some