No Gap Between Roof Sheathing Panels

Lay sheets in rows with the long edge horizontal to the roof bottom.

No gap between roof sheathing panels.

The minimum osb panel size is 24 inches in any direction and each sheet end must rest on a rafter. Apa recommends a 1 8 inch space between panel edge and end joints. When you sandwich the layers so there is no air gap you only get the insulation value of the closed foam in the prodex material. If the wood structural panels are tightly butted there is no room for expansion and buckling can occur.

Roof trusses must be dry when sheathing a roof with osb to prevent mold growth in the roof and coverage gaps as the trusses dry and shrink. Provide a 1 8 inch gap. That can mean costly time consuming callbacks. Some older h clips do not provide a built in gap.

By no means am i an expert on insulation but from what i ve read you need to have an air gap between the foil facing and the exterior material like the shingles or sheathing under it. Not always required but a good idea. Sometimes plywood or osb was installed right on top of the boards. What h clips do h clips provide additional stiffness between bearing points for the unsupported edges of wood panel plywood or osb roof sheathing along with the necessary 1 8 gap for expansion as shown below illustrated on a bag of simpson h clips.

However it is considered good practice to leave a 1 8 gap between sheets and that is also recommended by apa but it is not required. Unless you provide a small gap between the exterior face of the osb and the back surface of the foam sheathing to provide for some hygric redistribution. The recommended maximum gap between roof sheathing boards for low quality 3 tab shingles is 1 4 inch. Stagger the panels over the roof with 2 supports between panel ends.

If asphalt shingles are installed over sheathing with gaps exceeding 1 4 inch over time these gaps may telegraph through and become visible. Avoid butting osb panels tightly leave a 3 mm 1 8 inch gap between the osb panels to allow for expansion. Or if you are perfect with your rainwater control such as when you use a fully adhered membrane think roof membrane standing up applied to a wall.