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.

Insulating an a frame roof. 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. We recently purchased a small a frame in zone 4a as a vacation home. When the rafters are exposed such as in timber frame houses this technique is. The outside of the wall lets water vapor exit to the outside air so the insulation can stay dry.

Now for the roof build up. The construction of the cabin is fairly rudamentary. Box out light fixtures. 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.

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. Wet insulation doesn t insulate and wet studs will rot quickly. 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. Water is insulation s enemy. Over that i will run two layers of 2x4s 15 to hold the insulation in the cavitiy and create venting in the 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.

In typical lumber frame construction roof insulation is placed between rafters and then covered up with drywall. I will then put foam in that cavitiy 14. There is currently no insulation or ceiling.