Roof Sheathing Direction

How to correctly install plywood or osb roof sheathing.

Roof sheathing direction.

Position the first piece of plywood or oriented strand board sheathing on the bottom edge of the rafter tails at one end of the roof. Check the nailing surface is level step 2. And scroll down to see more details on each with installation hints and tips below. Wind loads perpendicular to a wall are similar to floor and roof loads and installing sheathing horizontally makes walls better at resisting wind pressure.

The main one is the structure turning into a parallelogram where the studs are no longer perpendicular to the ground. Ventilate the roof according to current building codes step 3. Properly fasten panels including fastening and spacing hints step 4. But if you snap it at 40 inches then the sheathing will not project over the subfascia or true fascia.

This opens the door to the possibility of water damage by letting gravity work against you. Why is the strength axis important for roof sheathing but not for corner. Roof sheathing attaches to the surface of the rafters or trusses to form the structural skin of the roof. I assume this means the panel should be applied with the long dimension across the studs yet the builder had installed the long dimension parallel to studs.

When you think of using a diagonal brace to support a wall you want to get both ends as far apart as possible. On roofs and floors sheathing is installed perpendicular to supports because this is the orientation that results in the strongest roof or floor. It spans the rafters to support the roofing and in the case of panel sheathing such as plywood or osb it acts as a diaphragm with the walls to resist horizontal loads. The surface stamp indicated that the strength axis of the panel ran in the long direction see photo below.

When the roof sheathing is used as a structural diaphragm as it typically is in high wind and seismic hazard areas the structural integrity of the diaphragm can be compromised by a continuous vent see figure a below left. The same policy goes for roof sheathing as for hanging drywall you get more strength by spanning more rafters joists studs and offsetting the joints. Maintain ridge nailing by adding additional blocking set back from the ridge or by using vent holes see. When sheathing a roof the first step is to snap a line so that the first row goes on straight.