Page 461 - 2018_IRC

ROOF ASSEMBLIES

3.3. Underlayment shall be attached using R905.2.1 Sheathing requirements. Asphalt shingles shall
metal or plastic cap nails with a nominal be fastened to solidly sheathed decks.
cap diameter of not less than 1 inch (25 R905.2.2 Slope. Asphalt shingles shall be used only on
mm). Metal caps shall have a thickness roof slopes of two units vertical in 12 units horizontal (17-
of not less than 32-gage sheet metal. percent slope) or greater. For roof slopes from two units
Power-driven metal caps shall have a vertical in 12 units horizontal (17-percent slope) up to four
thickness of not less than 0.010 inch units vertical in 12 units horizontal (33-percent slope),
(0.25 mm). Minimum thickness of the double underlayment application is required in accordance
outside edge of plastic caps shall be with Section R905.1.1.
0.035 inch (0.89 mm).
R905.2.3 Underlayment. Underlayment shall comply
3.4. The cap nail shank shall be not less than with Section R905.1.1.
0.083 inch (2.11 mm) for ring shank cap
nails and 0.091 inch (2.31 mm) for R905.2.4 Asphalt shingles. Asphalt shingles shall comply
smooth shank cap nails. Cap nail shank with ASTM D3462.
shall have a length sufficient to penetrate R905.2.4.1 Wind resistance of asphalt shingles.
through the roof sheathing or not less Asphalt shingles shall be tested in accordance with
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than / inch (19 mm) into the roof ASTM D7158. Asphalt shingles shall meet the classifi-
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sheathing. cation requirements of Table R905.2.4.1 for the appro-
R905.1.2 Ice barriers. In areas where there has been a his- priate ultimate design wind speed. Asphalt shingle
tory of ice forming along the eaves causing a backup of packaging shall bear a label to indicate compliance
water as designated in Table R301.2(1), an ice barrier shall with ASTM D7158 and the required classification in
be installed for asphalt shingles, metal roof shingles, min- Table R905.2.4.1.
eral-surfaced roll roofing, slate and slate-type shingles, Exception: Asphalt shingles not included in the
wood shingles and wood shakes. The ice barrier shall con- scope of ASTM D7158 shall be tested and labeled in
sist of not fewer than two layers of underlayment cemented accordance with ASTM D3161. Asphalt shingle
together, or a self-adhering polymer-modified bitumen packaging shall bear a label to indicate compliance
sheet shall be used in place of normal underlayment and with ASTM D3161 and the required classification in
extend from the lowest edges of all roof surfaces to a point Table R905.2.4.1.
not less than 24 inches (610 mm) inside the exterior wall R905.2.5 Fasteners. Fasteners for asphalt shingles shall
line of the building. On roofs with slope equal to or greater be galvanized steel, stainless steel, aluminum or copper
than eight units vertical in 12 units horizontal (67-percent roofing nails, minimum 12-gage [0.105 inch (3 mm)]
slope), the ice barrier shall also be applied not less than 36 shank with a minimum / -inch-diameter (9.5 mm) head,
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inches (914 mm) measured along the roof slope from the complying with ASTM F1667, of a length to penetrate
eave edge of the building. through the roofing materials and not less than / inch
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Exception: Detached accessory structures not contain- (19.1 mm) into the roof sheathing. Where the roof sheath-
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ing conditioned floor area. ing is less than / inch (19.1 mm) thick, the fasteners shall
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R905.2 Asphalt shingles. The installation of asphalt shingles penetrate through the sheathing.
shall comply with the provisions of this section. R905.2.6 Attachment. Asphalt shingles shall have the
minimum number of fasteners required by the manufac-
turer’s approved installation instructions, but not less than
TABLE R905.2.4.1
CLASSIFICATION OF ASPHALT ROOF SHINGLES
MAXIMUM ULTIMATE DESIGN MAXIMUM BASIC WIND SPEED, a
V ASD FROM TABLE R301.2.1.3 ASTM D7158 ASTM D3161
WIND SPEED, V ult SHINGLE CLASSIFICATION SHINGLE CLASSIFICATION
FROM FIGURE R301.2(5)A (mph) (mph)
110 85 D, G or H A, D or F
116 90 D, G or H A, D or F
129 100 G or H A, D or F
142 110 G or H F
155 120 G or H F
168 130 H F
181 140 H F
194 150 H F
For SI: 1 foot = 304.8 mm; 1 mile per hour = 0.447 m/s.
a. The standard calculations contained in ASTM D7158 assume Exposure Category B or C and a building height of 60 feet or less. Additional calculations are
required for conditions outside of these assumptions.

436 2018 INTERNATIONAL RESIDENTIAL CODE ®
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