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.
Gap between roof sheathing and batt insulation.
Still you need to make sure that the gap is not more than 1 8 inch.
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.
Batts should cover the top plate of the exterior wall but not block the venting.
Here is a fact.
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.
Generally spray foams have to be applied by a professional.
Use baffles between each rafter space to prevent it from being blocked see figure 5 11.
When you found gaps or channels between the insulation pieces it is better to leave it that way so the air could get into the house.
You can then apply batt insulation around the foam without worrying too much about the air space.
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.
If you use air permeable insulation and it is not in direct contact with the air barrier in this case the plywood roof deck you will experience convective.
Apply a 2 inch layer of spray foam insulation r 10 to r 12 directly to the interior surface of the roof sheathing.
Leave gaps between panels you need a gap on the roof so your room could breathe.