Page 459 - 2018_IRC

ROOF ASSEMBLIES

TABLE R905.1.1(2)—continued
UNDERLAYMENT APPLICATION
MAXIMUM ULTIMATE DESIGN MAXIMUM ULTIMATE DESIGN
ROOF COVERING SECTION
WIND SPEED, V ult < 140 MPH WIND SPEED, V ult  140 MPH
For roof slopes from two and one-half units verti-
1
cal in 12 units horizontal (2 / :12), up to four units
2
vertical in 12 units horizontal (4:12), underlay-
ment shall be not fewer than two layers applied as
follows: starting at the eave, apply a 19-inch strip
of underlayment parallel with the eave. Starting at
the eave, apply 36-inch-wide strips of underlay-
Clay and R905.3 ment felt, overlapping successive sheets 19 Same as Maximum Ultimate Design Wind Speed,
V < 140 mph, except all laps shall be not less
ult
concrete tile inches. End laps shall be 4 inches and shall be off- than 4 inches.
set by 6 feet.
For roof slopes of four units vertical in 12 units
horizontal (4:12) or greater, underlayment shall be
not fewer than one layer of underlayment felt
applied shingle fashion, parallel to and starting
from the eaves and lapped 2 inches. End laps shall
be 4 inches and shall be offset by 6 feet.
For roof slopes from two units vertical in 12 units
Metal roof shingles R905.4
horizontal (2:12), up to four units vertical in 12
units horizontal (4:12), underlayment shall be two
Mineral-surfaced R905.5 layers applied in the following manner: apply a
roll roofing 19-inch strip of underlayment felt parallel to and
starting at the eaves. Starting at the eave, apply
Slate and slate-type R905.6 36-inch-wide sheets of underlayment, overlapping
shingles
Apply in accordance with the manufacturer’s successive sheets 19 inches. End laps shall be 4
installation instructions. inches and shall be offset by 6 feet.
Wood shingles R905.7 For roof slopes of four units vertical in 12 units
horizontal (4:12) or greater, underlayment shall be
one layer applied in the following manner: under-
Wood shakes R905.8 layment shall be applied shingle fashion, parallel
to and starting from the eave and lapped 4 inches.
End laps shall be 4 inches and shall be offset by 6
Metal panels R905.10 feet.
For roof slopes from two units vertical in 12 units
horizontal (2:12), up to four units vertical in 12
units horizontal (4:12), underlayment shall be two
layers applied in the following manner: apply a 19-
inch strip of underlayment felt parallel to and start-
ing at the eaves. Starting at the eave, apply 36-inch-
wide sheets of underlayment, overlapping succes-
sive sheets 19 inches. Distortions in the underlay-
ment shall not interfere with the ability of the Same as Maximum Ultimate Design Wind Speed,
Photovoltaic R905.16 shingles to seal. End laps shall be 4 inches and shall V < 140 mph, except all laps shall be not less
shingles ult
be offset by 6 feet. For roof slopes of four units ver- than 4 inches.
tical in 12 units horizontal (4:12) or greater, under-
layment shall be one layer applied in the following
manner: underlayment shall be applied shingle
fashion, parallel to and starting from the eave and
lapped 2 inches. Distortions in the underlayment
shall not interfere with the ability of the shingles to
seal. End laps shall be 4 inches and shall be offset
by 6 feet.
For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 mile per hour = 0.447 m/s.

434 2018 INTERNATIONAL RESIDENTIAL CODE ®
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