Roof Sheathing Structure

Type

• Plywood has become the most prominent type roof decking since the middle of the 20th century. It replaced a system of wooden planks nailed to the rafters, which might still be seen on some older homes. Plywood sheathing and a similar product called oriented strand board, or OSB, come in 4-by-8-foot panels. The panels typically measure 3/8-inch or 1/2-inch thick, depending on the spacing of the rafters.

Layout

• Drawing a plan for installation on graph paper before applying the sheathing helps the job go more smoothly. Measuring the height and width of your roof gives you the number of 4-by-8-foot panels you will need. The plan should indicate where you will need partial panels as opposed to full-sized ones. You must also take into account that the top row of panels should never be less than 16 inches wide. You may need to adjust the width of the panels in the first row to avoid this problem.

Intallation

• The recommended procedure for installation is to start at the bottom corner of the roof and work your way up, according to the book, "Ultimate Guide to House Framing." The long side of the panel should lay perpendicular to the rafters. Every end joint of each panel should intersect a rafter and then be fastened to it. The second row should start with a panel half of the normal 4-by-8-foot size to make sure the joints do not intersect the joints of the first row. You need to continue staggering succeeding rows as you work.

Fastening

• Panels fasten to the rafters with 8d nails that have spiral threads or ring shanks. Proper spacing requires positioning the nails 6 inches apart on the rafters at the panel ends and 12 inches apart on other rafters. The nail should penetrate the plywood and attach itself firmly to the supporting rafter. H-clips, stainless steel fasteners that you attach to panels to stiffen their edges, may be required by some local building codes.