TI 809-53
CEMP-ET
Appendix 2-1. Roof Slopes and Fire Ratings for Various Materials
01 May 1999
Slope (Inches/Foot)
Comments
Ratings
1/4
1
2
3
4
5
6
7
8
9
Low Slope (Hydrostatic)
Slope %
Membrane Roofing
2
8
17 25 33
50
Built-Up
Asphalt - 4 ply/gravel
Minimum slope on new roofs is 2%
Class A on both combustible and non-combustible
(1/4 in./ft). Aggregate surfacing is not decks.
suitable for slopes over 25% (3 in./ft).
The maximum slope for ASTM D312 Type I
asphalt is 2% (1/4 in./ft), for Type II--8.3%
(1:12), for Type III--25% (3:12) limits
except in very hot climate where Type IV
is needed.
Asphalt - 4 ply/cap sheet
Class A or B rating can be achieved on slopes
Minimum slope on new roofs is 4%
(1/2 in./ft). Slippage limits slope to
of 3 in./ft, or less for noncombustible deck
3 in./ft. Capsheet can be used for
construction. Class A or B rating can be
vertical flashing with adequate top
achieved on slopes of 1 in./ft, for combustible
nailing.
deck construction.
Coal tar pitch - 4 ply/gravel
Current Air Force criteria limit the use ofggregate surfacing permits Class A rating
A
coal tar to roofs with slopes of 1/8 in./fton both combustible and non-combustible
,
or less. Cold flow and slippage limit sldecks.
ope
to 1/4 in./ft, with fiberglass reinforcement
and 1/2 in./ft, with organic felt reinforce-
ment in most climes. Slopes over 1/4 in./ft
are not recommended.
Modified Bitumen
Modified bitumen - smooth coated
Minimum slope on new roofs is 2%
With field applied fire resistant coatings,
(1/4 in./ft). Torched and adhesively
Class A or B rating can be achieved for use
bonded systems required at slopes above r noncombustible decks generally up to 8.3%
ove
8.3% (1:12).
(1 in./ft) maximum slope. Class A or B rating
can be achieved for use over combustible
decks with additional ply sheets and/or
insulations generally up to 4% (1/2 in./ft).
2-28
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