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ROOF DECKS |
If units are out of level by more than 1/4 " (6 mm), joints must be grouted to a smooth even finish. A layer of approved JM roof insulation solid
mopped in hot steep asphalt to the primed deck is required prior to installation of any JM built-up or modified bitumen system. The individual
pieces of roof insulation are restricted to a maximum size of 4' x 4' (1.22 m x 1.22 m). Mechanical attachment of roof insulation or membrane
systems directly to this deck type is not acceptable to JM under any condition.
4.9 Pre-Cast Gypsum
4.9.1 These are factory-formed units, usually tongue-and-groove, and metal bound. The manufacturer’s recommendations should be followed
carefully in design of the supporting structure and in placement and attachment. Pre-cast gypsum provides a satisfactory base for nailing.
Fasteners to be considered should be approved by the fastener manufacturer, the deck manufacturer, and JM for suitability. Certain fasteners
may require predrilled holes. Contact the fastener manufacturer for detailed installation instructions.
4.9.2 A layer of approved JM roof insulation, solid mopped in hot steep asphalt to a nailed base sheet is required prior to installation of any JM
built-up or modified bitumen system.
4.10 Application of Pre-Cast Units
A. |
All units should be installed in accordance with approved erection drawings and details based on
architectural drawings. |
B. |
Planks should be clipped or mechanically secured to joists or beams as required by the deck
manufacturer. |
C. |
Planks should be neatly cut to fit around all openings and projections through the roof. Openings larger
than 8" x 8" (203 mm x 203 mm) should be framed with wood curbs. |
D. |
Care should be taken not to overload deck units by placing any superimposed loads on the deck. This
overloading could include rooftop mounted equipment, excessive construction loads, and units
suspended from the underside of the deck which could cause deflection resulting in ponding of water. |
E. |
Protect deck units from the weather and install roofing and/or insulation to dry decks only. |
4.11 Wood Tongue-and-Groove Boards, Planks, and Plywood
4.11.1 Wood was one of the original materials used in roof deck construction and is still widely used because of its economy, ease of
application, and appearance. When properly installed, it makes an excellent substrate for a roofing system. Wood roof decks tend to expand
and contract with changes in humidity conditions. For this reason, it is unacceptable to attach roof insulation, built-up roofing or modified
bitumen roofing directly to a wood deck with hot asphalt or by heat welding.
4.11.2 Wood board decks should have the following characteristics:
A. |
Boards should be kiln-dried and either tongue-and-grooved, ship-lapped or splined. Tongue-and-grooved
or splined lumber is preferred to square-edge materials, as possible shrinkage of the boards may open
joints and affect the roof system by causing buckling or splitting of the membrane. |
B. |
Boards should not be warped and should have a minimum of knot holes and cracks. Knot holes, and
cracks greater in width than 1/4 " (6 mm), should be filled or covered with sheet metal, nailed in place,
being careful that the metal is smoothly installed so the roofing membrane will not be damaged. |
C. |
Boards should have a minimum nominal width of 4" (102 mm), a maximum nominal width of 6" (152 mm)
and a minimum nominal thickness of 1" (25 mm). |
D. |
Boards should be securely fastened to the purlins for adequate strength and rigidity. |
E. |
Nailing must be done with long enough nails to secure the deck material to the joists or purlins without
backing out of supporting members. |
F. |
Any preservative treatments must be of a non-oil, non-creosote type. The preservative should be one
employing a water-borne salt treatment. Refer to Paragraph 4.2.2 for additional information. |
G. |
For BUR, SBS and PAO modified bitumen membranes, a dry sheathing paper (red rosin paper is
commonly used) must be laid over the deck to divorce the roof membrane from possible movement of the
boards, to prevent free resins in the deck from adhering the base sheet to the wood, and to prevent
asphalt from dripping through openings between the boards. Sheathing paper is not required over
plywood. |
4.11.3 Structural Sheathing is a manmade wood product used in the construction of roof decks. Today the common types are plywood and
oriented strand board (OSB). The American Plywood Association defines these products as follows:
A. |
Plywood: All veneer panels consist of an odd number of cross-laminated layers, each layer consisting of
one or more plies. Panels should meet all of the prescriptive or performance provisions of U.S. Product
Standard PS-1 81/ANSI A199.1 for construction and industrial plywood. Fire-retardant treated plywood is
unacceptable without certification from the manufacturer that the product will not be structurally damaged
over the life of the roof due to the treatment process. |
B. |
Oriented Strand Board: Panels of compressed strand-like particles arranged in layers (usually three to
five) oriented in right angles to one another. Panels should meet all of the prescriptive or performance
provisions of U.S. Product Standard PS-1 81/ANSI A199.1 for construction and industrial plywood. |
