measure the width of the panel minus the actual
thickness of the fascia material. Use this chalk line to
position the upper edge of the sheathing panels. If the
roof rafters are at right angles to the ridge and plates,
this line will place the sheathing panels parallel to the
outer ends of the rafters.
Be particularly careful when
handling sheet material on a roof
during windy conditions. You may be
thrown off balance and possibly off the
roof entirely. Also, the sheet may be
blown off the roof and strike someone.
Notice in figure 3-2 that sheathing is placed before
the trim is applied. Sheathing is always placed from the
lower (eaves) edge of the roof up toward the ridge. It
can be started from the left side and worked toward the
right, or you can start from the right and work toward
the left. Usually, it is started at the same end of the house
from which the rafters were laid out.
The first sheet of plywood is a full 4- by 8-foot
panel. The top edge is placed on the chalk line. If the
sheathing is started from the left side of the roof, make
sure the right end falls in the middle of a rafter. This must
be done so that the left end of the next sheet has a surface
upon which it can bear weight and be nailed.
The plywood is placed so that the grain of the top
ply is at right angles (perpendicular) to the rafters.
Placing the sheathing in this fashion spans a greater
number of rafters, spreads the load, and increases the
strength of the roof. Figure 3-3 shows plywood panels
laid perpendicular to the rafters with staggered joints.
Note that a small space is left between sheets to allow
The sheets that follow are butted against spacers
until the opposite end is reached. If there is any panel
hanging over the edge, it is trimmed after the panel is
fastened in place. A chalk line is snapped on the
sheathing flush with the end of the house, and the panel
is then cut with a circular saw. Read the manufacturers
specification stamp and allow proper spacing at the ends
and edges of the sheathing. This will compensate for any
swelling that might take place with changes in moisture
The cutoff piece of sheathing can be used to start
the second course (row of sheathing), provided it spans
two or more rafters. If it doesnt span two rafters, start
the second course with a half sheet (4 by 4) of plywood.
Figure 3-3.-Plywood roofing panel installation.
It is important to stagger all vertical joints. All
horizontal joints need blocking placed underneath or a
metal clip (ply clip). Ply clips (H clips or panel clips)
are designed to strengthen the edges of sheathing panels
between supports or rafters. The use of clips is deter-
mined by the rafter spacing and specifications (see
The pattern is carried to the ridge. The final course
is fastened in place, a chalk line is snapped at the top
edge of the rafters, and the extra material cut off. The
opposite side of the roof is then sheeted using the same
When nailing plywood sheathing, follow the project
specifications for nailing procedures. Use 6d common
smooth, ring-shank or spiral thread nails for plywood
1/2 inch thick or less. For plywood more than 1/2 inch
but not exceeding 1 inch thick, use 8d common smooth,
ring-shank or spiral thread nails. When using a nail gun
for roof sheathing, follow all applicable safety
In this section, well discuss the two most common
types of roof decking you will encounter as a Builder:
plank and wood fiber.
Plank roof decking, consisting of 2-inch (and
thicker) tongue-and-groove planking, is commonly