Proper Roof Sheathing

Material

• The basic type of roof sheathing comes in sheets that are nailed to the roof framing. Plywood and oriented strand board, or OSB, are the two main types of material used to make these sheets of sheathing. OSB tends to swell more than plywood when exposed to moisture, but it lacks the soft spots that sometimes occur in plywood. Also, you can purchase larger sheets of OSB. The building codes for your area may indicate a particular type of sheathing or building requirements for the project, so check those first.

Preparation

• For level sheathing installation, you need a level, sturdy frame underneath. If you aren't comfortable with roof framing, hire an experienced roofing contractor to tackle that portion of the job. The rafter tails are typically cut before the sheathing is installed. The sub-fascia board is then attached to the cut rafter tails to guide the sheathing installation. Review the roofing plans to determine exactly where the overhangs are and where you need to install the sheathing.

Installation

• Sheathing installation begins along the bottom edge of the roof. Align the first piece of sheathing with one side of the roof and the bottom edge of the trusses. Each piece is nailed into place through the trusses underneath. Using a hammer to drive the nails gives you better control and a stronger attachment to the frame. Work across the bottom row until you reach the end, allowing the sheathing to overhang that end. Move up to the next row of sheathing and work across again. The joints on the rows should not align as this makes a weaker roof. Stagger the joints of the sheathing for greater durability, allowing overhang on the end pieces of each row.

Finishing

• Once all sheathing is in place, you are able to cut off the extra edge pieces. A snapped chalk line creates a guide for cutting off the extra plywood or OSB with a circular saw. If the sheathing overhangs at the top along the peak, trim off the excess at this point as well. The sheathed roof is ready for the installation of drip edges and felt before the roofing material is installed.