Problem: Water leakage through wood roofing.
Cause: Excessive exposure length, no interlay between shake courses, and improper joint locations.
Solutions: Install wood shingles and shakes according to local building code requirements.
- Prevent the movement of wind-driven rain through the shingled roof to the attic or roof cavity by overlapping the shingles or shakes correctly.
Most local building codes require that the exposure of wood shakes to wind, rain or sun shall not exceed 7-1/2 inches (190 mm) for shakes not less than 18 inches (450 mm) long; and 10 inches (250 mm) for shakes not less than 24 inches (600 mm) long.
Correct exposure for wood shingles is a function of shingle length, grade and roof slope. No. 1 grade shingles that are 16 inches (400 mm) long can have a maximum exposure of 5 inches (125 mm); those that are 18 inches (450 mm) long can have a maximum exposure of 5-1/2 inches (140 mm); and those that are 24 inches (600 mm) long can have a maximum exposure of 7-1/2 inches (190 mm) as shown in Figure 14.
Figure 14 - Wood Shingle Exposure
- Apply a strip of breather-type roof felt a minimum of 18 inches (450 mm) wide over the top portion of the shakes and rest it on the roof sheathing.
Place the bottom end of the felt a distance of twice the weather exposure above the butt. This felt underlay acts as a baffle and prevents wind-driven rain or snow from penetrating the roof cavity.
- Space shingles 1/4 inch (6mm) apart, and offset them at the joints in adjacent courses by not less than 1-1/2 inches (40 mm) so that the joints in alternate courses are staggered. Shakes shall be spaced 1/4 inch (6 mm) to 3/8 inch (9 mm) apart and offset at the joints in adjacent courses by not less than 1-1/2 inches (40 mm) so that joints in alternate courses are staggered as shown in Figure 15.
Figure 15 - Correct Deck Preparation & Nailing Of Wood Shingles
Note 1: Deck sheathing
Note 2: Breather-type felt interlay.
Note 3: 1/4 inch (6mm) for shingles - 1/2 inch (13 mm) for shakes.
Note 4: Wood decking spaced.
Note 5: Eave protection.
Note 6: Offset the joists by 1 1/2 inches (38 mm) minimum.
Note 7: 3/4 inch edge nailing - nails placed 1 1/2 inch (38 mm) above lapping joints.
Note 8: Wood shakes
Additional information on roofs and roofing