Need advice on insulating knee wall attic – GreenBuildingAdvisor

You don’t typically need faced insulation on an attic floor, especially with a vented attic. I would recommend adding more insulation though, perpindicular to the first layer and on top of the joists. Code is R49 in most places, which is a good target to shoot for.

For the wall, you really want an air barrier on all sides, so that includes the attic side. This is less of an issue with dense batt material like mineral wool, but still a good idea. I typically use polyiso for this, which also gets you additional R value for the wall. 1″ or thicker is good (I used 3″ in my own home).

With crawlspaces, you’re really best off encapsulating with poly and insulating the walls with rigid foam and the rim joist with either rigid foam or spray foam. Batts in the joists is not ideal regardless of the type of batt you use.

Bill