4.
Fluid-applied roofing systems
19.6
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:
1.
Use tapered insulation, sloped structural systems, or level
structural system with sloped fill to achieve the required
slope.
2.
Do not use NRCA defined "One-way slope" (Sloping to a level
valley). See NRCA - "Tapered Roof Insulation Systems."
3.
Use NRCA defined "Two-Way slope" (actually sloping in four
directions).
19.7
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.
19.8
Locate drains at points of maximum deck deflection; generally at
midspan of the deck between supports where possible.
19.9
Design single-ply ballasted roofing systems using Factory Mutual
Criteria for wind force resistance. The following are Factory
Mutual Criteria:
a.
Loss Prevention Data 1-7, "Wind Forces on Buildings and Other
Structures"
b.
Loss Prevention Data 1-28, "Insulated Steel Deck"
c.
Loss Prevention Data Technical Advisory Bulletin 1-29,
"Loose-Laid Ballasted Roof Coverings"
d.
Loss Prevention Data 1-49, "Perimeter Flashing".
19.10 Anchor insulation to deck. Loose laid insulation is not permitted
except for protective membrane roof insulation system.
19.11 Specify quality of ballast material in VA Guide Specifications.
19.12 Locate overflow scuppers in parapet walls at top of membrane so
that ponding does not exceed high point of slopes.
19.13 Where the roof deck is to become a future floor slab, design the
roof system as follows:
a.
Depress roof slab as required by VA Design and Construction
Procedure, "Future Vertical Expansion", paragraph 2d.
b.
Provide a separation between the roof system and the roof deck
(future floor slab).
c.
Design for easy removal of the roofing system down to the roof
deck.
d.
Detail connections for future columns and exterior walls to
prevent water infiltration into the roof system.
19.14 Use 200 mm (8 inch) high base flashing at walls and penetrations.
Do not use pitch pockets or similar penetration seals.
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