June 99
9.5
Design low-slope roof systems with a positive slope a
minimum of 1:50 (0.25 inch per foot) up to a maximum of
1:12 (1.0 inch per foot) 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).
9.6
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.
9.7
Locate drains at points of maximum deck deflection;
generally at midspan of the deck between supports where
possible.
9.8
Design single-ply ballasted roofing systems using Factory
Mutual Criteria for wind force resistance. The following are
Factory Mutual Criteria:
a. Loss Prevention Data 1-28, "Insulated Steel Deck"
b. Loss Prevention Data Technical Advisory Bulletin 1-29,
"Loose-Laid Ballasted Roof Coverings"
c. Loss Prevention Data 1-49, "Perimeter Flashing".
9.9
Anchor insulation to deck. Loose laid insulation is not
permitted except for protective membrane roof insulation
system.
9.10
Specify quality of ballast material in VA Guide
Specifications.
9.11
Locate overflow scuppers in parapet walls at top of
membrane so that ponding does not exceed high point of
slopes.
9.12
Use 200 mm (8 inch) high base flashing at walls and
penetrations. Do not use pitch pockets or similar
penetration seals.
VA Design Guide -- National Cemetery Administration
Page 5 -7
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