Insulating An A Frame Roof

When the rafters are exposed such as in timber frame houses this technique is.

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. 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. In typical lumber frame construction roof insulation is placed between rafters and then covered up with drywall. Now for the roof build up.

First i will frame out with 2x6s on top of the roof a cavitiy for insulation 13 following the perimeter of the cabin. All too often people discover that the a frame home they purchased has inadequate insulation or worse yet none at all. We recently purchased a small a frame in zone 4a as a vacation home. I will then put foam in that cavitiy 14.

Over that i will run two layers of 2x4s 15 to hold the insulation in the cavitiy and create venting in the roof. The construction of the cabin is fairly rudamentary. There is currently no insulation or ceiling. 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.

It creates a breeding ground for mold and mildew and ruins the air trapping pockets that block heat flow. Wet insulation doesn t insulate and wet studs will rot quickly. 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. 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.

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. The outside of the wall lets water vapor exit to the outside air so the insulation can stay dry.