Roof coverings shall be applied in accordance with the applicable provisions of this section and the manufacturer's installation instructions. Unless otherwise specified in this section, roof coverings shall be installed to resist the component and cladding loads specified in Table R301.2(2), adjusted for height and exposure in accordance with Table R301.2(3).
Underlayment for asphalt shingles, clay and concrete tile, metal roof shingles, mineral-surfaced roll roofing, slate and slate-type shingles, wood shingles, wood shakes and metal roof panels shall conform to the applicable standards listed in this chapter. Underlayment materials required to comply with ASTM D 226, D 1970, D 4869 and D 6757 shall bear a label indicating compliance to the standard designation and, if applicable, type classification indicated in Table R905.1.1(1). Underlayment shall be applied in accordance with Table R905.1.1(2). Underlayment shall be attached in accordance with Table R905.1.1(3).
Exceptions:
1. As an alternative, self-adhering polymer-modified bitumen underlayment complying with ASTM D 1970 installed in accordance with both the underlayment manufacturer's and roof covering manufacturer's instructions for the deck material, roof ventilation configuration and climate exposure for the roof covering to be installed, shall be permitted.
2. As an alternative, a minimum 4-inch-wide (102 mm) strip of self-adhering polymer-modified bitumen membrane complying with ASTM D 1970, installed in accordance with the manufacturer's instructions for the deck material, shall be applied over all joints in the roof decking. An approved underlayment for the applicable roof covering for maximum ultimate design wind speeds, Vult, less than 140 miles per hour shall be applied over the entire roof over the 4-inch-wide (102 mm) membrane strips.
TABLE R905.1.1(1) UNDERLAYMENT TYPES
TABLE R905.1.1(2) UNDERLAYMENT APPLICATION
TABLE R905.1.1(3) UNDERLAYMENT ATTACHMENT
Exceptions:
1. As an alternative, self-adhering polymer-modified bitumen underlayment complying with ASTM D 1970 installed in accordance with both the underlayment manufacturer's and roof covering manufacturer's instructions for the deck material, roof ventilation configuration and climate exposure for the roof covering to be installed, shall be permitted.
2. As an alternative, a minimum 4-inch-wide (102 mm) strip of self-adhering polymer-modified bitumen membrane complying with ASTM D 1970, installed in accordance with the manufacturer's instructions for the deck material, shall be applied over all joints in the roof decking. An approved underlayment for the applicable roof covering for maximum ultimate design wind speeds, Vult, less than 140 miles per hour shall be applied over the entire roof over the 4-inch-wide (102 mm) membrane strips.
TABLE R905.1.1(1) UNDERLAYMENT TYPES
| ROOF COVERING | SECTION | MAXIMUM ULTIMATE DESIGN WIND SPEED, Vult < 140 MPH | MAXIMUM ULTIMATE DESIGN WIND SPEED, Vult ≥ 140 MPH |
| Asphalt shingles | R905.2 | ASTM D 226 Type I ASTM D 4869 Type I, II, III or IV ASTM D 6757 | ASTM D 226 Type II ASTM D 4869 Type IV ASTM D 6757 |
| Clay and concrete tile | R905.3 | ASTM D 226 Type II ASTM D 2626 Type I ASTM D 6380 Class M mineral- surfaced roll roofing | ASTM D 226 Type II ASTM D 2626 Type I ASTM D 6380 Class M mineral- surfaced roll roofing |
| Metal roof shingles | R905.4 | ASTM D 226 Type I or II ASTM D 4869 Type I, II, III or IV | ASTM D 226 Type II ASTM D 4869 Type IV |
| Mineral-surfaced roll roofing | R905.5 | ASTM D 226 Type I or II ASTM D 4869 Type I, II, III or IV | ASTM D 226 Type II ASTM D 4869 Type IV |
| Slate and slate-type shingles | R905.6 | ASTM D 226 Type I ASTM D 4869 Type I, II, III or IV | ASTM D 226 Type II ASTM D 4869 Type IV |
| Wood shingles | R905.7 | ASTM D 226 Type I or II ASTM D 4869 Type I, II, III or IV | ASTM D 226 Type II ASTM D 4869 Type IV |
| Wood shakes | R905.8 | ASTM D 226 Type I or II ASTM D 4869 Type I, II, III or IV | ASTM D 226 Type II ASTM D 4869 Type IV |
| Metal panels | R905.10 | Manufacturer's instructions | ASTM D 226 Type II ASTM D 4869 Type IV |
TABLE R905.1.1(2) UNDERLAYMENT APPLICATION
| ROOF COVERING | SECTION | MAXIMUM ULTIMATE DESIGN WIND SPEED, Vult < 140 MPH | MAXIMUM ULTIMATE DESIGN WIND SPEED, Vult ≥ 140 MPH |
| Asphalt shingles | R905.2 | 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. 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: 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. | Same as Maximum Ultimate Design Wind Speed, Vult < 140 mph except all laps shall be not less than 4 inches. |
| Clay and concrete tile | R905.3 | For roof slopes from two and one-half units vertical in 12 units horizontal (21/2:12), up to four units vertical in 12 units horizontal (4:12), underlayment shall be a minimum of 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 underlayment felt, overlapping successive sheets 19 inches. For roof slopes of four units vertical in 12 units horizontal (4:12) or greater, underlayment shall be a minimum of 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. | Same as Maximum Ultimate Design Wind Speed, Vult < 140 mph except all laps shall be not less than 4 inches. |
| Metal roof shingles | R905.4 | Apply in accordance with the manufacturer's installation instructions. | 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, and fastened sufficiently to hold in place. 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: underlayment 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 feet. |
| Mineral-surfaced roll roofing | R905.5 | ||
| Slate and slate-type shingles | R905.6 | ||
| Wood shingles | R905.7 | ||
| Wood shakes | R905.8 | ||
| Metal panels | R905.10 |
For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm
TABLE R905.1.1(3) UNDERLAYMENT ATTACHMENT
| ROOF COVERING | SECTION | MAXIMUM ULTIMATE DESIGN WIND SPEED, Vult < 140 MPH | MAXIMUM ULTIMATE DESIGN WIND SPEED, Vult ≥ 140 MPH |
| Asphalt shingles | R905.2 | Fastened sufficiently to hold in place | The underlayment shall be attached with corrosion-resistant fasteners in a grid pattern of 12 inches between side laps with a 6-inch spacing at the side laps. Underlayment shall be attached using metal or plastic cap nails or cap staples with a nominal cap diameter of not less than 1 inch. Metal caps shall have a thickness of not less than 32-gage sheet metal. Power- driven metal caps shall have a minimum thickness of 0.010 inch. Minimum thickness of the outside edge of plastic caps shall be 0.035 inch. The cap nail shank shall be not less than 0.083 inch for ring shank cap nails and 0.091 inch for smooth shank cap nails. Staples shall be not less than 21 gage. Cap nail shank and cap staple legs shall have a length sufficient to penetrate through the roof sheathing or not less than 3/4 inch into the roof sheathing. |
| Clay and concrete tile | R905.3 | ||
| Metal roof shingles | R905.4 | Manufacturer's installation instructions. | The underlayment shall be attached with corrosion-resistant fasteners in a grid pattern of 12 inches between side laps with a 6-inch spacing at the side laps. Underlayment shall be attached using metal or plastic cap nails or cap staples with a nominal cap diameter of not less than 1 inch. Metal caps shall have a thickness of at least 32-gage sheet metal. Power-driven metal caps shall have a minimum thickness of 0.010 inch. Minimum thickness of the outside edge of plastic caps shall be 0.035 inch. The cap nail shank shall be not less than 0.083 inch for ring shank cap nails and 0.091 inch for smooth shank cap nails. Staples shall be not less than 21 gage. Cap nail shank and cap staple legs shall have a length sufficient to penetrate through the roof sheathing or not less than 3/4 inch into the roof sheathing. |
| Mineral-surfaced roll roofing | R905.5 | ||
| Slate and slate-type shingles | R905.6 | ||
| Wood shingles | R905.7 | ||
| Wood shakes | R905.8 | ||
| Metal panels | R905.10 |
For SI: 1 inch = 25.4 mm.
In areas where there has been a history of ice forming along the eaves causing a backup of water as designated in Table R301.2(1), an ice barrier shall be installed for asphalt shingles, metal roof shingles, mineral-surfaced roll roofing, slate and slate-type shingles, wood shingles and wood shakes. The ice barrier shall consist of not fewer than two layers of underlayment cemented together, or a self-adhering polymer-modified bitumen sheet shall be used in place of normal underlayment and extend from the lowest edges of all roof surfaces to a point not less than 24 inches (610 mm) inside the exterior wall line of the building. On roofs with slope equal to or greater than 8 units vertical in 12 units horizontal, the ice barrier shall also be applied not less than 36 inches (914 mm) measured along the roof slope from the eave edge of the building.
Exception: Detached accessory structures not containing conditioned floor area.
Exception: Detached accessory structures not containing conditioned floor area.