Gap Between Roof Sheathing And Batt Insulation

Unless you have at least a 1 gap between the roof deck and roxul with both ridge soffit venting putting putting foil facers on the interior side is going to create a moisture trap.

Gap between roof sheathing and batt insulation.

Apply a 2 inch layer of spray foam insulation r 10 to r 12 directly to the interior surface of the roof sheathing. Batts secured to the deck with insulation hangers between top chords or more commonly tension cables secured at the ridge and eaves with eye hooks to prevent fall out. Hole in the roof sheathing near the center of your roof so that you can install a doghouse above the roof to act as a vent outlet. You can then apply batt insulation around the foam without worrying too much about the air space.

Batts should cover the top plate of the exterior wall but not block the venting. This will keep the surface warm and help minimize condensation. Use baffles between each rafter space to prevent it from being blocked see figure 5 11. Generally spray foams have to be applied by a professional.

Here is a fact. Still you need to make sure that the gap is not more than 1 8 inch. The only way you can make venting work on this type of roof is if you can maintain a gap of at least 6 inches between the top of your insulation and the underside of your roof sheathing and if you can cut a 2 ft. Shingles roofing felt stackups are on the boundary between class i class ii vapor retardency when dry at about 0 1 perms and when the roof is wet there is.

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.