Insulating An A Frame Roof

Roof covering does not allow water vapor to exit to the outside air so the roof on an a frame needs special treatment.

Insulating an a frame roof.

Wet insulation doesn t insulate and wet studs will rot quickly. 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 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. When the rafters are exposed such as in timber frame houses this technique is.

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. Now for the roof build up. It creates a breeding ground for mold and mildew and ruins the air trapping pockets that block heat flow. 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.

The construction of the cabin is fairly rudamentary. In typical lumber frame construction roof insulation is placed between rafters and then covered up with drywall. All too often people discover that the a frame home they purchased has inadequate insulation or worse yet none at all. First i will frame out with 2x6s on top of the roof a cavitiy for insulation 13 following the perimeter of the cabin.

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 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. The problem is the rafters are too small to get enough insulation inbetween.

Water is insulation s enemy. We recently purchased a small a frame in zone 4a as a vacation home. There is currently no insulation or ceiling.