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Sheathing
Shingles and
shakes shall be applied over spaced sheathing. Spaced
sheathing is usually 1" x 4" of 1" x 6" softwood boards.
Solid
sheathing is acceptable and may be required in seismic
regions or under treated shakes and shingles. It is
recommended on shake applications in areas where wind-driven
snow is common. Solid sheathing is usually wafer-board
panels or plywood which provides a smooth base for roofing.
Shingles
There are two
acceptable methods for application of spaced sheathing. One
is to space 1" x 4" boards to coincide with the weather
exposure of the shingles (Figure 1). Thus, if the shingles
are to be laid at 5½" to the weather, the sheathing boards
would also be spaced at 5½" on center. In this method of
application each shingle is nailed to the center of the 1" x
4" board. In the second method of application, where 1" x 6"
boards are used, two courses of shingles are nailed to each
1" x 6" board. (Figure 2) up to and including 5½" weather
exposure. Although not commonly used, 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" boards
spaced on centers equal to the weather exposure at which the
shakes are to be laid - but never more than 7½" for 18"
shakes and 10" for 24" shakes on roof installations.
When 1" x 4" spaced sheathing is installed at 10" on center,
additional 1" x 4" boards must be installed between the
sheathing 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
insulation value.
Special care
should be taken when installing the felt interlays over
spaced sheathing to ensure that an effective baffle is
formed (Figure 3). 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 |
