How to Insulate Finished Room Above Garage
LESLIE: John in Georgia, you’ve got The Money Pit. How can we help you today?
JOHN: Yes, ma’am. I’m thinking about finishing off a room up on top of the garage. And I’m going to use spray foam – I plan to – and spray it under the sheathing – the roofing sheathing – and follow the roof line on up, oh, about 10 feet above the – make it a 10 – a vault-type ceiling and – over top of the attic.
My understanding is that if I spray foam right under the sheathing, that it may void shingle warranties. And I was going to put baffles up there, underneath the sheathing, and then spray the foam on top of that but do I have to put that on every rafter or every other one or every third one? Or how many do I put that under or don’t I have to put baffles?
TOM: So, John, what’s the shape of this roof? Is it an A-shape?
JOHN: Yes, A-shaped.
TOM: OK. So it’s A-shape. What’s the depth of the roof rafter? Two by eight? Two by ten?
JOHN: I think it is eight. Eight. I think it’s eight.
TOM: Two by eight?
TOM: OK. So the way I would do this then is I would not use spray-foam insulation. I would use 6 inches of fiberglass insulation and I would leave the inch-and-a-half that’s left – or the 2 inches that’s left – as the ventilation space. So this way, air would enter the soffits, it would go up between the insulation and the roof sheathing and exit at the ridge.
TOM: And that kind of gives you everything that you want to accomplish.
TOM: Alright. Well, good luck with that project. Thanks so much for calling us at 888-MONEY-PIT.