Need help with my detached garage roof assembly
mapnerd
| Posted in Green Building Techniques on
Hi,
Our plans specify a detached garage connected to breezeway/screen porch, which is then connected to the house. I planned to stick frame the garage (2×4 @ 24″oc walls w/ 1″ exterior XPS). For the roof, I’ve got 2×6 rafters @ 24″oc, then 1/2″ plywood sheathing, then 30# felt, then standing seam steel roof panels. Should I add some rigid foam up there? Would that go above or below the plywood sheathing? Do I need to be concerned about venting?
Thanks
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Replies
Are you heating the garage? Where are you located?
No need to heat the garage, but don't want to freeze if we're out there for a while. I'm in Omaha, NE (zone 5).
Michael,
Most people don't insulate outbuildings that we not be heated or cooled with a space conditioning system.
Your comment -- that you "don't want to freeze if we're out there for a while" -- makes it clear that you are more worried about winter than summer.
Ceiling or roof insulation in an unheated garage will not make a garage any warmer. It might even make it colder, since the only two sources of heat for an unconditioned garage are the engine of a recently driven car (a minor source of heat) and the sun, which occasionally warms the roof (and therefore the interior, as long as there is no roof insulation) of a garage on sunny, snowless days during the winter.
Should I use a waterproof membrane instead of building felt or both?
Standing seam roofing IS a waterproof membrane, and is typically installed over #30 felt. Nothing more is needed or desirable.