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ROOF DECKS |
4.5.4 Roof insulation of the proper thickness to afford adequate support for the roofing system and typical construction traffic, must be installed
over all steel decks. To prevent damage to the first or bottom layer of insulation, JM requires that the thickness of this layer of roof insulation be
in accordance with the chart below:
4.5.5 Roof insulation must be uniformly secured to the steel deck with approved mechanical fasteners. Fasteners must penetrate at least 3/4 "
(19 mm) through the steel deck. Hot asphalt or cold adhesive is not acceptable. JM will not issue a roof guarantee for any roof system in which
the insulation is applied directly over a steel deck with only a cold or hot adhesive.
4.5.6 JM requires attachment of the base layer of insulation to steel decks by mechanical fasteners in bituminous systems. Insulation installed
in two layers should preferably have the first layer mechanically fastened and the second layer secured in hot steep asphalt. When done in this
fashion, the individual pieces of roof insulation in the second and succeeding layers must be restricted to a maximum size of 4' x 4' (1.22 m x
1.22 m).
4.5.7 Insulation that is loose from the deck or not uniformly adhered not only adds to blow-off potential, but also can contribute to premature
failure of the roof membrane.
4.5.8 To reduce attachment problems with insulation to steel decks, Factory Mutual requires the use of mechanical fasteners. The approved
number and types of fasteners for the field of the roof for the insulation board being used is given in the current Factory Mutual Approval Guide.
Additional fasteners are required by Factory Mutual Loss Prevention Data Sheet 1-28 at the corners and perimeters. The size of the corners
and perimeters are calculated by:
1. 0.1 times the building’s lesser plan dimension.
2. 0.4 times the eave height.
3. In no case shall the corners and perimeters be less than 4 ft.
Factory Mutual also requires increasing the number of fasteners in the roof perimeter to a rate of 150% of that in the field, and the number of
fasteners in the roof corners to a rate of 175% of that in the field.
See the current Factory Mutual Loss Prevention Data Sheet 1-28 and 1-29 for more details.
4.6 Poured Concrete Decks
4.6.1 Properly placed poured structural concrete decks of good mix can provide a satisfactory deck for application of most roof systems.
Control joints properly installed, and a relatively smooth surface, are primary considerations. Concrete decks must be dry. Decks must be
primed with Concrete Primer and the primer allowed to dry thoroughly before asphalt is applied. The quantity of mopping bitumen used to
attach insulation or membrane to a poured concrete deck will be affected by the smoothness of the deck. The individual pieces of roof
insulation are restricted to a maximum size of 4' x 4' (1.22 m x 1.22 m). 4.6.2 In Regions 1 and 2 when thermal roof insulation is not required,
all built-up or modified bitumen roofing components are to be solidly mopped in hot asphalt to the primed surface of the deck. In cases where
there is a concern about residual pour moisture, a base sheet may be spot mopped using 12" (305 mm) diameter, machine applied spots,
24" (610 mm) o.c. This technique must be approved in writing by a JM Technical Services Specialist prior to application.
4.6.3 In Region 3, base felts may be spot mopped in hot asphalt to primed concrete decks. If insulation is to be installed directly to a poured
concrete deck, it should be solidly mopped in hot asphalt to the primed deck.
