No Gap Between Roof Sheathing Panels

Not always required but a good idea.

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. Provide a 1 8 inch gap. 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. If the wood structural panels are tightly butted there is no room for expansion and buckling can occur.

Sometimes plywood or osb was installed right on top of the boards. Some older h clips do not provide a built in gap. 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. Stagger the panels over the roof with 2 supports between panel ends.

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. That can mean costly time consuming callbacks. Avoid butting osb panels tightly leave a 3 mm 1 8 inch gap between the osb panels to allow for expansion.

Plywood and oriented strand board osb like all wood products will expand or shrink slightly with changes in moisture content. 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. 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. 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.

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. Lay sheets in rows with the long edge horizontal to the roof bottom. If asphalt shingles are installed over sheathing with gaps exceeding 1 4 inch over time these gaps may telegraph through and become visible.