Page 77 - 2018 National Home Improvement

2018 National Home Improvement Estimator, All Rights Reserved Page 60

Sheathing
A wavy roof surface is evidence that the sheathing has sagged. The only practical repair is to remove
and replace the sheathing. However, you may be able to nail new sheathing right over the old. This
saves both the labor of removing the old sheathing and a big cleanup job. Of course, you must remove
old sheathing that shows signs of decay or mold.

New sheathing that’s nailed over existing sheathing must be secured with longer nails than normally
used on roof sheathing because the nails still need to penetrate the framing 1-1/4” to 1-1/2”. You should
nail the sheathing edges at 6” spacing and nail to the intermediate framing members at 12” spacing.
Install sheathing with the long edge at right angles to the rafters. For a built-up roof, join panel edges
with plywood clips where edges don’t meet over a rafter. You can use 3/8”-thick sheathing for 16” rafter
spacing, which is the minimum thickness required. However, 1/2”-thick plywood is better, and is
required for heavy roofing materials such as clay or concrete tile. You’ll find that Oriented Strand Board
(OSB) sheathing costs less and works just as well as plywood sheathing.

Strip sheathing helps promote air circulation, which is an important consideration in any climate. Slate
and tile roofs are commonly installed on furring strips rather than plywood sheathing. However, strip
sheathing is not appropriate for asphalt shingle applications.

When replacing the roof cover, roof sheathing or roof supports, check the roof flashing for rust and
physical damage. Inadequate or damaged flashing could result in leaks. Replace any flashing that
shows signs of age. Then renew the caulking around chimneys and parapet walls.