Composition Shingle Roofing
A. ROOF DECK:
1. Roof deck must be solid sheathing, either plywood or original plank board construction. Any large voids must be replaced or covered with sheet metal.
2. Fill in between existing spaced sheathing boards is not allowed.
3. Shingle installation may not be applied directly over rigid insulation board.
4. Up to two overlays of composition shingles are allowed over original composition or wood shingles if the roof is in reasonable condition.
5. Shingle recovers over shakes or laminated composition shingles are not allowed.
6. Ventilation should be improved wherever practical.
B. UNDERLAYMENT:
1. A minimum 15# felt underlayment is required. IRCC recommends 30# felt.
2. No underlayment is required when roofing over existing composition shingles when the pitch is at least 4/12. IRCC recommends a minimum 30# felt underlayment.
3. A minimum 30 # underlayment should be used over wood shingles.
4. A mineral surfaced cap sheet or two layers of 30# felt are needed in all valleys where shingles are used in lieu of a metal valley.
5. All sheet metal valleys shall receive a felt underlayment equal to the roofing underlayment.
6. Slopes less than 4/12 and greater than 2/12 should have a minimum double layer of 15# felt installed in shingle fashion. A single underlayment of 30# felt is not adequate. IRCC recommends a double layer of 30# felt installed in shingle fashion.
7. Application of asphalt shingles on slopes of 2/12 or less should be over an impermeable membrane where the shingles are installed for aesthetic purposes only.
C. FASTENERS:
1. Nails shall be EG type, 7/16” head, long enough to penetrate 3/4” into or through the sheathing board.
2. Staples shall be galvanized type, 7/8” crown minimum, long enough to penetrate 3/4” into or through the sheathing board.
3. Shorter fasteners are acceptable for use at overhangs and eaves to
minimize penetration of the visible underside.
4. Fasteners shall be located as to penetrate through all laminations and the selvage top of the underlying shingle, generally four fasteners per shingle.
5. Additional fasteners may be required in high wind areas.
D. STARTER COURSE:
1. Starter may be 3 tab shingles or mineral surfaced cap sheet cut down to 9” width.
2. Starter may be fastened separately or with the first course of field shingles.
3. Low nailing of starter shingles is not recommended.
4. Supplemental spot sealing of first course over starter course is not required.
E. VALLEYS:
1. 28 gauge, 18” wide, W type metal valley may be used. The shingles should overlap a minimum of 6” on each flange.
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Metal Valley |
2. A “California Valley” consists of shingles lapped 12” past the valley center line and covered with a “bleeder strip” parallel with the center of the valley Shingles lapped from the other side are cut along the bleeder strip.
3. Shingles may be woven across the valley 12” onto the opposite side.
California Valley
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Woven Valley |
4. No fasteners may be installed within 6” of the center of any of these valleys.
F. CHIMNEY FLASHING:
1. May be reused if in serviceable condition. When roofing over an existing roof, the base flange and step shingles should be lifted and installed into the new roof
2. If counter flashing is replaced, it may be fastened to the chimney with concrete nails and sealed with a good exterior caulk.
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Chimney Flashing |
G. ROOF JACKS AND PLUMBING VENTS:
1. May be reused if in serviceable condition. When roofing over an existing roof, flashings should be lifted and installed with the new shingles.
2. Plumbing pipes may be sealed to the flashing with flashing tape, rubber collar, or plastic cement.
3. Painting of flashing to blend with the roofing is desirable but not required.
4. Exposed galvanized nails in base flashing are acceptable.
H. MISCELLANEOUS FLASHINGS:
1. Edge metal is required to cover exposed edges of plywood.
2. Edge metal is not required but is desirable to cover exposed edges of the original roof when overlaying an existing roof.
3. Painting of edge metal is not required.
4. When flashing against a vertical side wall:
a. New flashings may be installed if feasible. If new flashings are installed on the exterior of the wall, the flashing should be counter flashed with wood or metal sealed to the wall with a good exterior caulk.
b. The old flashings may be reused if in serviceable condition. The flashings shoulld be lifted and installed with the new shingles except in applications as noted below.
c. When roofing over composition, the old flashing may remain in the old roof. The last 3” of the new shingle is embedded in plastic cement. A bead of plastic cement should be applied on top of the shingle against the vertical wall.
d. When roofing over wood shingles, the old flashing may remain in the old roof. Install a 6” wide strip of mineral surfaced cap sheet next to the wall. Cover the strip with plastic cement and install the new shingles. Apply a bead of plastic cement on top of the shingles against the wall.
I. HIP AND RIDGE:
1. Ridge should be installed with one nail on each side penetrating into the sheathing at least 3/4”.
2. Blind nailing is recommended. If nails are exposed, they must be galvanized.
3. Supplemental surface nailing in addition to blind nailing is acceptable and is desirable in high wind areas.
4. Spacing of ridge shingles shall match that of the field shingles unless otherwise specified by manufacturer.
J. BUILDING DEPARTMENT INSPECTIONS:
1. Pre-inspection of roof overlays should be required.
2 In-progress inspections should include spot checks of decking, plywood nailing, shingle application, and flashing installation.
3. Final inspections should be done from the ground if inspectors do not provide their own ladder.
