3.9.1.2 Low-slope roof systems include but are not limited to the following
roofing membranes with roof insulation:
A. Bituminous built-up roofing systems
B. Modified bituminous roofing systems
C. Single-ply sheet roofing system
D. Fluid-applied roofing systems
3.9.1.3 Re-roofed areas shall conform to this Article.
3.9.1.4 Where alterations or repairs are required to over 40 percent of flat
roof, consider entire re-roofing.
3.9.2 POLICY
No roofs shall be dead flat; design all roofs with slope to roof drains or
gutters.
3.9.3 DESIGN LAYOUT OF LOW-SLOPE ROOFS
3.9.3.1 Design low-slope roof systems with a positive slope: a minimum of
1:50 (0.25 in. per ft.) up to a maximum of 1:12 (1.0 in. per ft.) to drains:
A. Use tapered insulation, sloped structural systems, or level structural
system with sloped fill to achieve the required slope.
B. Do not use NRCA defined "One-way slope" (Sloping to a level valley). See
NRCA "Tapered Roof Insulation Systems."
C. Use NRCA defined "Two-Way slope" (actually sloping in four directions).
3.9.3.2 Use a uniform square grid to lay out roof slopes to drains. Roofs
shall not slope to level valleys, but may have one-way slopes to gutters at
gravel-stop edges.
3.9.3.3 Locate drains at points of maximum deck deflection; generally at mid
span of the deck between supports where possible.
3.9.4 ROOFING SELECTION
It is very important to select the right roofing system. Some of the factors
that may influence the roofing choice are:
A. The shape of the building and roof
B. The location of the drains, whether exterior or interior
C. Aesthetic considerations
D. Roof and insulation attachment methods that are dictated by the deck type
E. The insulating values desired for energy conservation and HVAC sizing
F. The type of building use and operations. For example, the water vapor
generated from a swimming pool, or emissions from a boiler plant, may dictate
the choice of roofing
G. Thermal insulation versus storm water management
3.9.5 ANCHORAGE OF INSULATION
Anchor insulation to deck. Loose laid insulation is not permitted except for
protective membrane roof insulation system.
ARCHITECTURAL DESIGN MANUAL
3-8
BUILDING ENVELOPE
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