v10climber
Active member
Hi All. First time poster but I've used this forum for years to gain knowledge. I've spent hours and hours reading threads here in GJ trying to decide what to do about insulating a new detached garage that I'm building and can't quite seem to figure out the best way to go about this.
Slab is down and in January they'll be putting up a stick built 28x35. 2x6 walls and 2x6 storage trusses. Shortly after going up the garage will get electrical, HVAC and sheetrock. Insulating the walls is a pretty easy problem to solve. My plan is to do a large part of the wiring myself and then fiberglass batts in the walls with drywall. Easy enough.
The roof and attic trusses are presenting a much larger problem. I'm not going to be spending much time in the roof storage area but I'll have lots of things up there I don't want subjected to the heat/humidity of FL. So the attic space must be conditioned. As far as I can tell there are two approaches to this. One is a hot roof with closed cell foam sprayed directly to the roof decking and blocked soffits and no ridge vent. The other is to install rafter vents to the roof decking that go from the soffit straight to the ridge vent and provide roof ventilation then fiberglass batting between the top chords.
The contractor doing the building "shell" suggested spray foam but I have a few reservations:
1. Cost. I was planning to DIY the rafter vent and batt solution. Assuming 3 to 4k for closed cell foam on the ceiling based on prices I've seen quoted in here.
2. Owens Corning says shingles installed on a hot roof are not covered by the warranty. Probably not a problem but would hate to have a failure that isn't covered.
3. If I foam the roof do I also have to foam the walls or can I do FG batts in the walls and closed cell foam on the roof?
And the real kicker of all of this is that none of the solutions seem to have a very high R value that can be contained within a 2x6. Anything thicker than a 2x6 eats into headroom in the attic area which would be kind of annoying. I'm zone 2 which recommends R-30 min in the roof but 1" for rafter vent means really just space for R-13 left over if I'm using fiberglass. Could I do 1" of closed cell spray foam straight to the roof decking and then an R-13 FG batt for some extra insulation that's cheaper than 3-4" of closed cell foam?
Slab is down and in January they'll be putting up a stick built 28x35. 2x6 walls and 2x6 storage trusses. Shortly after going up the garage will get electrical, HVAC and sheetrock. Insulating the walls is a pretty easy problem to solve. My plan is to do a large part of the wiring myself and then fiberglass batts in the walls with drywall. Easy enough.
The roof and attic trusses are presenting a much larger problem. I'm not going to be spending much time in the roof storage area but I'll have lots of things up there I don't want subjected to the heat/humidity of FL. So the attic space must be conditioned. As far as I can tell there are two approaches to this. One is a hot roof with closed cell foam sprayed directly to the roof decking and blocked soffits and no ridge vent. The other is to install rafter vents to the roof decking that go from the soffit straight to the ridge vent and provide roof ventilation then fiberglass batting between the top chords.
The contractor doing the building "shell" suggested spray foam but I have a few reservations:
1. Cost. I was planning to DIY the rafter vent and batt solution. Assuming 3 to 4k for closed cell foam on the ceiling based on prices I've seen quoted in here.
2. Owens Corning says shingles installed on a hot roof are not covered by the warranty. Probably not a problem but would hate to have a failure that isn't covered.
3. If I foam the roof do I also have to foam the walls or can I do FG batts in the walls and closed cell foam on the roof?
And the real kicker of all of this is that none of the solutions seem to have a very high R value that can be contained within a 2x6. Anything thicker than a 2x6 eats into headroom in the attic area which would be kind of annoying. I'm zone 2 which recommends R-30 min in the roof but 1" for rafter vent means really just space for R-13 left over if I'm using fiberglass. Could I do 1" of closed cell spray foam straight to the roof decking and then an R-13 FG batt for some extra insulation that's cheaper than 3-4" of closed cell foam?