Appendix 2-1. Roof Slopes and Fire Ratings for Various Materials
01 May 1999
Low Slope (Hydrostatic)
Membrane Roofing (cont'd)
17 25 33
TPO - ballasted
Minimum slope on new roofs is 2%
Ballast provides Class A rating on non-
(1/4 in./ft). Ballast movement limits
combustible and combustible decks when used
in excess of 39 Kg/m2 (8 lb/ft2).
slope to 17% (2:12).
Including Structural Standing Seam
Standing seams with factory applied seal- eptance is primarily based upon uplift
Metal, Architectural Standing Seam,
ant have greatly reduced the seam leaks nsiderations. Architectural metal roofing over
and Lap Seam Metal Roofing
experienced by older lap seam metal a combustible deck requires an approved
roofing. A minimum slope of 4% (1/2 in./fterlayment.
is required to provide positive drainage,
reduce leak potential, and to prevent
Steep (Hydrokinetic) Roofing
Shingles require minimum 33% (4 in./fClass A rating on all slopes above 17% (2:12).
slope to prevent leakage unless an under-
layment is used. No upper limit on slope
except that field applied tab seal wind
protection must be provided on slopes
over 175% (21 in./ft).
Asphalt - Organic
Same as Asphalt--Fiberglass above Class C rating on all slopes above 17% (2:12)
suitable for watershed protection.
Shakes - Wood
Materials require minimum 4 in./ft slopNoo e have Class A. Several manufacturers have
Class B using special fire resistant treatments
for the wood in conjunction with a special