Insulating An A Frame Roof

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.

Insulating an a frame roof.

We recently purchased a small a frame in zone 4a as a vacation home. There is currently no insulation or ceiling. First i will frame out with 2x6s on top of the roof a cavitiy for insulation 13 following the perimeter of the cabin. Roof covering does not allow water vapor to exit to the outside air so the roof on an a frame needs special treatment.

The problem is the rafters are too small to get enough insulation inbetween. Over that i will run two layers of 2x4s 15 to hold the insulation in the cavitiy and create venting in the 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. Now for the roof build up.

I will then put foam in that cavitiy 14. Water is insulation s enemy. 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. It creates a breeding ground for mold and mildew and ruins the air trapping pockets that block heat flow.

The outside of the wall lets water vapor exit to the outside air so the insulation can stay dry. When the rafters are exposed such as in timber frame houses this technique is. 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. 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.

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. Wet insulation doesn t insulate and wet studs will rot quickly.