No Gap Between Roof Sheathing Panels

If the wood structural panels are tightly butted there is no room for expansion and buckling can occur.

No gap between roof sheathing panels.

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. Sometimes plywood or osb was installed right on top of the boards. Plywood and oriented strand board osb like all wood products will expand or shrink slightly with changes in moisture content. The minimum osb panel size is 24 inches in any direction and each sheet end must rest on a rafter.

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. Stagger the panels over the roof with 2 supports between panel ends. That can mean costly time consuming callbacks. 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.

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. Lay sheets in rows with the long edge horizontal to the roof bottom. Actually panels marked sized for spacing simply mean that they are slightly smaller to allow for the recommended 1 8 gap see attached apa tt 055. Apa recommends a 1 8 inch space between panel edge and end joints.

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. Not always required but a good idea. The recommended maximum gap between roof sheathing boards for low quality 3 tab shingles is 1 4 inch. 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. 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. It doesn t mean that panel edge clips h clips are required although there are types of clips that will help with properly spacing the panels.