Page 457 - 2018_IRC

ROOF ASSEMBLIES

R903.4 Roof drainage. Unless roofs are sloped to drain over specified in Table R301.2(2), adjusted for height and expo-
roof edges, roof drains shall be installed at each low point of sure in accordance with Table R301.2(3).
the roof. R905.1.1 Underlayment. Underlayment for asphalt shin-
R903.4.1 Secondary (emergency overflow) drains or gles, clay and concrete tile, metal roof shingles, mineral-
scuppers. Where roof drains are required, secondary emer- surfaced roll roofing, slate and slate-type shingles, wood
gency overflow roof drains or scuppers shall be provided shingles, wood shakes, metal roof panels and photovoltaic
where the roof perimeter construction extends above the shingles shall conform to the applicable standards listed in
roof in such a manner that water will be entrapped if the pri- this chapter. Underlayment materials required to comply
mary drains allow buildup for any reason. Overflow drains with ASTM D226, D1970, D4869 and D6757 shall bear a
having the same size as the roof drains shall be installed label indicating compliance to the standard designation
with the inlet flow line located 2 inches (51 mm) above the and, if applicable, type classification indicated in Table
low point of the roof, or overflow scuppers having three R905.1.1(1). Underlayment shall be applied in accordance
times the size of the roof drains and having a minimum with Table R905.1.1(2). Underlayment shall be attached in
opening height of 4 inches (102 mm) shall be installed in accordance with Table R905.1.1(3).
the adjacent parapet walls with the inlet flow located 2 Exceptions:
inches (51 mm) above the low point of the roof served. The
installation and sizing of overflow drains, leaders and con- 1. As an alternative, self-adhering polymer-modi-
ductors shall comply with Sections 1106 and 1108 of the fied bitumen underlayment complying with
International Plumbing Code, as applicable. ASTM D1970 installed in accordance with both
the underlayment manufacturer’s and roof cover-
Overflow drains shall discharge to an approved loca- ing manufacturer’s instructions for the deck
tion and shall not be connected to roof drain lines. material, roof ventilation configuration and cli-
mate exposure for the roof covering to be
installed, shall be permitted.
SECTION R904
MATERIALS 2. As an alternative, a minimum 4-inch-wide (102
R904.1 Scope. The requirements set forth in this section shall mm) strip of self-adhering polymer-modified
apply to the application of roof covering materials specified bitumen membrane complying with ASTM
herein. Roof assemblies shall be applied in accordance with D1970, installed in accordance with the
this chapter and the manufacturer’s installation instructions. manufacturer’s installation instructions for the
Installation of roof assemblies shall comply with the applica- deck material, shall be applied over all joints in the
ble provisions of Section R905. roof decking. An approved underlayment for the
applicable roof covering for maximum ultimate
R904.2 Compatibility of materials. Roof assemblies shall design wind speeds, V , less than 140 miles per
ult
be of materials that are compatible with each other and with hour shall be applied over the entire roof over the
the building or structure to which the materials are applied. 4-inch-wide (102 mm) membrane strips.
R904.3 Material specifications and physical characteris- 3. As an alternative, two layers of underlayment
tics. Roof covering materials shall conform to the applicable complying with ASTM D226 Type II or ASTM
standards listed in this chapter. D4869 Type III or Type IV shall be permitted to
R904.4 Product identification. Roof covering materials shall be installed as follows in 3.1–3.4:
be delivered in packages bearing the manufacturer’s identify- 3.1. Apply a 19-inch-wide (483 mm) strip of
ing marks and approved testing agency labels required. Bulk underlayment parallel with the eave.
shipments of materials shall be accompanied by the same Starting at the eave, apply 36-inch-wide
information issued in the form of a certificate or on a bill of (914 mm) strips of underlayment felt,
lading by the manufacturer. overlapping successive sheets 19 inches
(483 mm). End laps shall be 4 inches
(102 mm) and shall be offset by 6 feet
SECTION R905 (1829 mm).
REQUIREMENTS FOR ROOF COVERINGS
R905.1 Roof covering application. Roof coverings shall be 3.2. The underlayment shall be attached with
corrosion-resistant fasteners in a grid
applied in accordance with the applicable provisions of this pattern of 12 inches (305 mm) between
section and the manufacturer’s installation instructions. side laps with a 6-inch (152 mm) spacing
Unless otherwise specified in this section, roof coverings at side and end laps.
shall be installed to resist the component and cladding loads

432 2018 INTERNATIONAL RESIDENTIAL CODE ®
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