GENERAL DESIGN DETAILS

Shingles (Cont'd)

In the second method of application, where 1"x 6" (25.4 mm x 152.4 mm) boards are used, two courses of shingles are nailed to each 1" x 6" (25.4 mm x 152.4 mm) board (Figure 2), up to and including 5 1/2" (139.7 mm) weather exposure. With 7 1/2 " (190.5 mm) weather exposures, the center of the sheathing board shall equal the distance of the weather exposure. Although not commonly used, a breather-type underlayment, such as roofing felt, may be applied over either solid or spaced sheathing.

Shakes

In shake application spaced sheathing is usually 1" x 6" (25.4 mm x 152.4 mm) boards spaced on centers equal to the weather exposure (Table 5, Page 24) at which the shakes are to be laid - but never more than 7 1/2" (190.5 mm) for 18" (457.2 mm) shakes and 10" (254 mm) for 24"(609.6 mm) shakes on roof installations. When 1" x 4" (25.4 mm x 101.6 mm) spaced sheathing is installed at 10" (254 mm) on center, additional 1" x 4" (25.4 mm x 101.6 mm) boards must be installed between the sheating boards. A solid deck is recommended in areas where wind-driven snow is encountered. Roofing felt interlay between the shake courses is required whether the sheathing is spaced or solid. The felt interlay acts as a baffle that prevents wind- driven snow or other foreign material from entering the attic cavity during extreme weather conditions. The interlays also increase the roof's insulating value. Special care should be taken when installing the felt interlays over spaced sheathing to ensure that an effective baffle is formed (Figure 3, Page 6). The felt should be applied over the top portion of the shakes and extend on to the spaced sheathing so that the bottom edge of the felt is positioned at a distance above the butt equal to twice the weather exposure. To be an effective baffle, the top of the felt must rest on the sheathing. The shakes should be placed so that the nails are driven through the upper portion of the sheathing board with the top of the roofing felt attached to the lower portion.