The structural deck serves two functions:
a) For structural resistance to gravity, wind and
As substrate for the roof system.
Design Factors. Structural decks must be designed with
consideration of the following design factors:
Slope for drainage;
Anchorage (for wind-uplift resistance);
Deck surface and joints;
Drainage. In new construction, provide slope for
drainage in the structural deck, when practicable, with minimum
slope of 1/2 inch per foot (4 percent). For reroofing, provide a
minimum slope for drainage of 1/4 inch per foot (2 percent).
(Refer to Section 10.) Provide saddles or crickets in valleys
and other locations requiring additional drainage-promoting
techniques. Locate drains at low points, i.e., at center of
simple spans and other locations of maximum vertical deflection.
Where provision of slope in the structural deck is
impracticable specify tapered (sloped) insulation to provide
slope. The choice between interior or exterior drains depends
upon building size and configuration and local climate. Provide
interior drains in cold climates where subfreezing temperatures
may create drain-blocking ice in exterior drains.
Design the primary drainage system to accommodate the
rainfalls listed in DM-3.01, Plumbing Systems. Where the roof is
bounded with perimeter parapets, design a scupper system as
secondary drainage, with bottom scupper elevations designed to
limit ponding depth to a structurally safe depth in case the
primary drains are clogged. Design perimeter scupper drains by