Insulating An A Frame Roof

We don t want to build a false roof or false ceiling but even with 2x12 and sprayfoam 10 5 x r6 you can barely get to the r60 i need in my state and that s outrageously expensive and heavy.

Insulating an a frame roof.

On new build or replacement pitched roofs the ideal build up would be insulation fitted over and then between the rafters giving a big boost for airtightness image credit. The roof is composed of asphalt shingle on top of plywood sheathing which is supported by sistered 2x8s rafters with a four foot span between rafters. Look for water stains on the roof sheathing or damp or moldy spots on attic joists and existing insulation as a clue to where leaks might be. A frame homes especially older ones can be difficult to insulate because many times there is not much space between the roof and the ceiling.

The problem is the rafters are too small to get enough insulation inbetween. All too often people discover that the a frame home they purchased has inadequate insulation or worse yet none at all. Roof covering does not allow water vapor to exit to the outside air so the roof on an a frame needs special treatment. First i will frame out with 2x6s on top of the roof a cavitiy for insulation 13 following the perimeter of the cabin.

There is currently no insulation or ceiling. I will then put foam in that cavitiy 14. Kingspan with a flat roof this issue does not arise but the u value constraint and the amount of insulation needed is just the same. In typical lumber frame construction roof insulation is placed between rafters and then covered up with drywall.

We recently purchased a small a frame in zone 4a as a vacation home. Wet insulation doesn t insulate and wet studs will rot quickly. Now for the roof build up. The outside of the wall lets water vapor exit to the outside air so the insulation can stay dry.

Over that i will run two layers of 2x4s 15 to hold the insulation in the cavitiy and create venting in the roof. It creates a breeding ground for mold and mildew and ruins the air trapping pockets that block heat flow. Box out light fixtures.