Sheathing a Roof

How to Sheath a Roof with Plywood or Oriented Strand Board (OSB)

By Mark J. Donovan

Sheathing a roof involves the process of installing exterior grade plywood or OSB waferboard to the roof rafters or trusses. The required plywood or OSB thickness will depend upon your local building code requirements, but typically it ranges from 3/8th to 3/4th inch thick.

How Much Roof Sheathing is Required

Measure the number of square feet of roof and divide by 32. There is 32 square feet in a 4’x8’ sheet of plywood or OSB. Then multiply this number by 1.15 and round up to the next hole number to determine the number of sheets to buy and to allow for an extra 15% of waste.

Tools Required for Sheathing a Roof

To sheath a roof you will need a chalk line, tape measure, claw hammer, circular skill saw and some ladders. I also highly recommend a nail gun and compressor. Sheathing a roof requires a great deal of nailing and a nail gun can really help to speed up the process as well as save on the forearm muscles.

Installing Roof Sheathing

First, the sheathing should be installed perpendicular to the roof rafters or trusses.

Second, sheath a roof one slope at a time. Third, sheathing should be installed starting at the eaves (outside edges) of the roof and then working your way up towards the roof ridge. However, before installing the first course of sheathing check to make sure that the roof rafter tails (outside ends) are straight. If they are not, snap a chalk line along the length of the eaves near the very edge of the roof rafter/truss tails to make sure you have a straight and perpendicular line to begin your first course of sheathing.

How to shingle roofs and roof valleys.

You can then trim each roof rafter tail relative to the snapped chalk line using your circular skill saw.

When installing the roof sheathing panels, make sure that they are installed so that their ends line up over the center of each roof rafter or truss so that you have a nailing surface for fastening abutting panels.

When it comes to fastening the roof sheathing panels to the roof rafters/trusses, typically nails should be applied every 6 inches along the edges of the panels, and every 12 inches in the center field of the panels.

This said, hold off nailing the vertical edges of the panels until you have installed the adjacent panels. This way you can flex the rafters if necessary to center them up underneath the abutting roof sheathing panels. Once you have checked that the roof rafters are centered underneath the abutting panels, you can then nail them into place. There are also metal clips that you can use to help fasten abutting roof sheathing panels together.

It is important that each adjacent row of roof sheathing be staggered so that vertical seams do not line up directly over one another. To do this, simply cut a sheet of plywood or OSB into two 4’x4’ sections. Start the second course of roof sheathing panels with one of the 4’x4’ sections. Then continue to work across the width of the roof with 4’x8’ panels. Alternate with full and half sheets as you continue to work your way up the roof line.

Asphalt Shingle Roofing Bid Sheet

When you near the far end of each course of roof sheathing you can either immediately trim the board to the proper length, or hold off and trim all the panels at once. Trimming all of the panels at once typically is the most efficient way. Simply snap a chalk line from the eave to the ridge along the outer edge, set your saw blade on your circular skill saw to the proper thickness, and cut away the excess sheathing.

Continue to work your way up towards the ridge by installing one course of sheathing panels after another. Again alternate starting each new course with full and half width panels to make sure adjacent panel vertical seams do not line up directly over one another. When you near the roof ridge, rip saw plywood / OSB panels accordingly to complete the sheathing. However, leave about a 1” opening at the top of the ridge to allow for air to exit the roof. Ridge vent will be installed over this gap to prevent water infiltration into the attic area.

To complete the roof sheathing, repeat the process on the remaining roof slopes.

For more help on Shingling Your Home’s Roof, see’s Asphalt Shingle Roofing Bid Sheet. The Asphalt Shingle Roofing Bid Sheet will help to ensure that your roof won’t end up with a blue tarp over it and a dumpster sitting in your yard for weeks as you wait for the roofing contractor to come back and finish roofing your home.

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