CEMP-ET
TI 809-53
01 May 1999
(1)
Uninsulated Decks.
(a) For adhered membrane systems, non-combustible/non-nailable decks such as poured
and precast concrete must be cured and dry. If moisture collects on the underside of a piece of glass
or loose membrane placed on the deck, the deck is too wet. The deck must be free of grit or sharp
edges, which could cut the membrane. The adhesive may require a special primer.
(b) If insulation is not used, non-combustible/nailable decks such as precast lightweight
planks and poured gypsum require a slip-sheet and a mechanically fastened system using fasteners
designed for that deck type.
(c) Combustible/nailable decks such as wood, plywood, and OSB require adhered or
mechanically fastened systems as the decks are unlikely to support the weight of ballast.
(2) Insulated Roofing Systems.
(a) For adhered membrane systems insulation may be attached to the deck with bitumen,
special adhesives, or more typically with mechanical fasteners.
(b) For mechanically attached systems each insulation board should receive a minimum
of two preliminary fasteners in addition to those used to secure the membrane.
j. Vapor Retarders. Two plies of bituminous felt mopped to the substrate and each other provide
an excellent vapor retarder for non-combustible decks. Where bitumen is to be avoided, metal foil,
kraft paper laminates, or plastic films (i.e., polyethylene sheeting meeting ASTM D4397) with taped
laps may be suitable following the recommendations of the manufacturer. When a roof system is used
as the cover of a freezer or cooler building a severe reverse vapor drive occurs. Vapor pressure is
higher outside the building and the primary vapor drive is towards the colder interior. EPDM is only a
fair vapor retarder. A foil layer with taped seams placed directly beneath the EPDM sheet reduces
permeance. Vented edges and roof vents should be avoided. The EPDM membrane or underlying
foil film needs to be completely sealed to the wall vapor retarder system. It may be better to separate
the cooler or freezer from the roof system by at least a 600 mm (2 ft.) air space. The vapor retarder
for the cooler or freezer is then placed on the exterior of the freezer box facing the air space. Bare,
black EPDM (or any other bare membrane) should not be used in coolers or freezers due to the high
solar load.
k.
Thermal Insulation and Heat Flow.
(1) Polyisocyanurate Insulation. For adhered systems the facers must be well adhered to the
isoboard and compatible with the bonding adhesive used. The EPDM membrane manufacturer should
specifically approve the faced insulation.
(2) Wood Fiber and Perlite Board. For adhered membranes wood fiber may be an
acceptable substrate. Perlite board is generally unacceptable due to its lower peel strength.
(3) Thermoplastic Foams. For ballasted membrane systems polystyrene foam (MEPS or
XEPS) with a minimum density of 16 kg/m2 (1 pcf) should be used.
(4) Thermal Bridging. When mechanical fasteners are used to secure the membrane there is
some conductive heat flow through the fasteners. This is obvious on a roof with frost or light snow, and
in a colder climate can lead to condensation, corrosion, or wind blow-off problems. Such systems
should not be used for high humidity buildings in cold regions.
l.
Membranes and Surfacings.
6-3
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