Page 458 - 2018_IRC

ROOF ASSEMBLIES

TABLE R905.1.1(1)
UNDERLAYMENT TYPES
MAXIMUM ULTIMATE DESIGN MAXIMUM ULTIMATE DESIGN
ROOF COVERING SECTION
WIND SPEED, V ult < 140 MPH WIND SPEED, V ult  140 MPH
ASTM D226 Type I ASTM D226 Type II
Asphalt shingles R905.2 ASTM D4869 Type I, II, III or IV ASTM D4869 Type III or Type IV
ASTM D6757 ASTM D6757
ASTM D226 Type II ASTM D226 Type II
ASTM D2626 Type I ASTM D2626 Type I
Clay and concrete tile R905.3
ASTM D6380 Class M mineral- ASTM D6380 Class M mineral-
surfaced roll roofing surfaced roll roofing
ASTM D226 Type I or II ASTM D226 Type II
Metal roof shingles R905.4
ASTM D4869 Type I, II, III or IV ASTM D4869 Type III or Type IV
ASTM D226 Type I or II ASTM D226 Type II
Mineral-surfaced roll roofing R905.5
ASTM D4869 Type I, II, III or IV ASTM D4869 Type III or Type IV
ASTM D226 Type I ASTM D226 Type II
Slate and slate-type shingles R905.6
ASTM D4869 Type I, II, III or IV ASTM D4869 Type III or Type IV
ASTM D226 Type I or II ASTM D226 Type II
Wood shingles R905.7
ASTM D4869 Type I, II, III or IV ASTM D4869 Type III or Type IV
ASTM D226 Type I or II ASTM D226 Type II
Wood shakes R905.8
ASTM D4869 Type I, II, III or IV ASTM D4869 Type III or Type IV
ASTM D226 Type II
Metal panels R905.10 Manufacturer’s instructions
ASTM D4869 Type III or Type IV
ASTM D4869 Type I, II, III or IV ASTM D4869 Type III or Type IV
Photovoltaic shingles R905.16
ASTM D6757 ASTM D6757
For SI: 1 mile per hour = 0.447 m/s.

TABLE R905.1.1(2)
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 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 starting at the eaves. Starting at the eave, apply 36-inch-
wide sheets of underlayment, overlapping successive sheets
19 inches. Distortions in the underlayment shall not interfere
with the ability of the shingles to seal. End laps shall be 4 Same as Maximum Ultimate Design
Asphalt shingles R905.2 inches and shall be offset by 6 feet. Wind Speed, V < 140 mph except all
ult
For roof slopes of four units vertical in 12 units horizontal laps shall be not less than 4 inches.
(4:12) or greater, underlayment 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.

(continued)

2018 INTERNATIONAL RESIDENTIAL CODE ® 433
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