Gap Between Roof Sheathing And Insulation

Of airspace between the top of the insulation and the back of the roof sheathing.

Gap between roof sheathing and insulation.

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. Apply adhesive along the connection between the roof sheathing and rafters in a continuous bead much like caulk around a bathtub or apply adhesive to two adjacent sides of 1 by 2 blocks 6 inches. There are no irc requirements for spacing wood sheathing that i am aware of. 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.

T he problem with the insulation against the sheathing expands. In the winter humidity from the house s interior will get past the insulation and come in contact with the cold roof sheathing where it will condense into water. An air space between the insulation and the bottom of the roof sheathing is desirable. Use baffles between each rafter space to prevent it from being blocked see figure 5 11.

Batts should cover the top plate of the exterior wall but not block the venting. Several local and international building codes recommend a minimum of 1 inch gap between the sheathing and insulation. The code calls for a minimum of 1 in. Unless you re bulk filling rafter bays between 2 10 or 2 8 rafters with closed cell spray foam this approach.

The gap between the roof sheathing and the insulation over a ceiling is varied between 1 and 3 inches. Roof sheathing panel spacing hints. 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. For best performance the airspace in the vent chute should be a minimum of 2 in.

If there is a roof leak the insulation will be damaged by the water leaving you with less insulating value. The moisture is held in place by the insulation which allows for damage to the framing and other building components. To maintain airflow leave a space of 38 to 50 mm 1 1 2 to 2 in between the top of the insulation and the underside of the roof sheathing.