Publication Number 490-324, August 1996
"After a Disaster Roof Repairs 2: Basic Materials" discussed minimum standards for materials. This leaflet deals only with installing the sheathing selected following guidelines in leaflet 2.
Best results come with replacing damaged sheathing with the same material as the undamaged section of the roof. In no case may a different thickness be used. Thickness may not be built up satisfactorily with felt, shingles, or furring on rafters or trusses. Roof strength usually depends upon the same thickness.
Under the multiple pressures of shortages of time, unskilled or unknown workers, materials, etc., it may be tempting to short cut or make do on repairs, but remember that a depreciated home and future expensive trouble can come with such a decision. You may receive insurance or other assistance now; later when problems reappear, you may bear those costs alone.
First, a word of general advice on applying sheathing to rafters. The most frequent problem with roofs is buckling and warping, caused mainly by improper spacing of solid sheathing materials. Roofs more than any other area of a house are exposed to extremely hot and cold temperatures. Roofing materials expand when hot and contract when cold, actually "breathing" much the same as the human body. This means that adequate cracks, about 1/16-1/8 inch (a little thicker than a 25-cent piece) must be left at joints between solid sheathing. Plenty of cracks are present with 1x6 sheathing, thus spacing is not as critical. Manufactured spacing clips are available to use in spacing sheets of material and serve only that purpose. If clips are not used, be careful to provide sufficiently wide cracks on all sides of each sheet of material used.
Plywood Sheathing: Joints must be placed over rafters. Space sheets as described earlier. Sheathing must continue over two or more spans. The face grain of the plywood must run across the roof rafters, parallel to the peak of the roof.
Particle Board Sheathing: This may be applied either parallel or perpendicular to rafters. Care must be taken to stagger applications so that four panel corners do not meet at one point. A minimum 1/16inch gap between boards is required. Do not nail within 3/8-inch of the panel edge. Provide a half-inch gap from masonry (i.e. walls, chimneys). Take care to over cut holes for fitting around vents, plumbing, etc. Do not force fit. Fastenings should be with three 8d nails or four 1.75-inch staples per rafter crossed.
Installed "breathing" sheathing will form a good base for the next layers of roofing, the roofing felt and asphalt shingles, which will be discussed "After a Disaster Roof Repairs 4: Basic Materials".
Based on information developed by Clemson Cooperative Extension following Hurricane Hugo. Revised for Virginia audiences by Virginia Cooperative Extension.
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