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.

No gap between roof sheathing panels.

Not always required but a good idea. Stagger the panels over the roof with 2 supports between panel ends. That can mean costly time consuming callbacks. Plywood and oriented strand board osb like all wood products will expand or shrink slightly with changes in moisture content.

Some older h clips do not provide a built in gap. Lay sheets in rows with the long edge horizontal to the roof bottom. 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. 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.

Sometimes plywood or osb was installed right on top of the boards. Avoid butting osb panels tightly leave a 3 mm 1 8 inch gap between the osb panels to allow for expansion. 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. 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.

If asphalt shingles are installed over sheathing with gaps exceeding 1 4 inch over time these gaps may telegraph through and become visible. 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. 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.

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. The recommended maximum gap between roof sheathing boards for low quality 3 tab shingles is 1 4 inch. 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.