Attic Insulation: Spray Foam vs Batts

schneism asks,

I have a bungelow house with a metal roof. IN the attic space I am planning to convert it into living space and would like to insulate and drywall is off. When I look at the underside of the roof I see there is boards running length-wise and a space of a few inches in between them. In the spaces in between I see the underside of the metal roof.

How would I go about insulating that? Would a spray insulation be best or batts? I am worried about condensation and making sure i do the job right. if spray, what happens in 10 years when i need a roof? Thanks for any help.

Our Answer

If you want to insulate under the roof itself Closed cell insulation is the only choice you have. Fiberglass will not seal and prevent condensation from forming within it. The result is rotting and in your case rusting metal from behind. The closed cell insulation will prevent interior humidity from being absorbed into it and condensing when it gets close to the underside of the roof.

When the roof requires replacement, the material (sheathing) that holds the metal will be used to nail the new shingles or roof material on. So it will not disrupt the insulation in any way. But you cannot simply spray this underside if there is boards that appear to be damaged from decay already. These will need to be changed or the foam will stick to it and make it difficult to removed. We have in the past placed 1/2 inch foam boards against these areas then foamed to prevent the foam from reaching the area to be changed. That works well. But depending on how much roof sheathing that would require replacement that can jack the cost of the job pretty high and fast.

Currently there are some real good rebate programs. By foaming the attic and doing the basement sill areas you can qualify for at least $1,500 back I believe in VA and even more if other items require updating as a result of the house becoming more tight from the foam job.

A complete home energy assessment should be performed by a BPI professional. He or she can help guide you through the maze of rebate programs as well as help you decide what would work best for your attic area.