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Discussion Starter · #1 ·
The space I'm trying to insulate is about 90 sq ft on the ceiling. I have a 70+ year old former garage with 2x4 framing. About half of the room is going to have a vaulted/cathedral/whatever ceiling. The other half has rafter ties, trusses and all that. It's the 'attic' portion I guess. I'm playing the hand I've been dealt. It's a tough structure to deal with and the previous owners made some very ill advised structural modifications. I'm trying to insulate three rafter bays, 24 on center each. Room is 11X15. I just got a new roof, and there are no vents. Messing with that might void the warranty. Vents down low are also problematic. I need a solution for insulating the vaulted portion of the ceiling.

I furred the rafters with 2x2s to give it a little more room and I'm not sure where to go next.

I thought about drilling several one inch holes in the rafters right next to the decking so I could vent to the 'attic' portion of the room, and then putting in 2x4 batts or foam board with spacers so I could leave a gap between the insulation and the roof decking.

I understand that the ideal solution for a 'hot roof' is closed cell spray foam. Called a contractor today and told them I just need 90 sq ft and they said it's $3500 to come to the job site. Everything on the web says don't try to DIY it, plus the kits start at around $300, and those kits don't include the suit and the respirator.

So here we are. I don't feel like I need that much of the spray foam and I wonder if umpteen spray cans of Great Stuff or something would do the job without the ridiculous cost...Or is there another way? If I use batts, installing baffles won't do me any good because there's nowhere to funnel the air.

This is not going to be code and I'm on a budget. Whatever I do is not going to have a super high R value. I just want to add some insulation without setting the stage for catastrophic mold damage and all that nasty stuff.

Any ideas?
 

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Discussion Starter · #4 · (Edited)
Sorry for the late reply. The lower vents are problematic because there's no overhang. And every rafter bay would have to have its own vent from the roof or there'd be no ventilation higher up the roof. It's just not possible to install an adequate ventilation system for this part of the room.

This is a 70 year old garage that was never meant to be drywalled or insulated. Nothing comes easy with this project.

I ended up buying one of those 240 board foot spray foam kits. Basically they give you 12 cans of closed cell spray foam (no mixing necessary), a gun attachment, goggles, and some gloves. Bought a Tyvek suit and a cheap respirator. I'm gonna have to plastic off the room from the rest of the house and borrow a box fan from everyone I know to ventilate it for a few days. It'll be an adventure.
 

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Insulation can really help to prevent the heat. There are a lot of insulation estimation calculator which can really help to find out how much investment you need to do insulation. I have recommendation for company which I have used in past. Check it here.
 

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Discussion Starter · #7 · (Edited)
Insulation can really help to prevent the heat. There are a lot of insulation estimation calculator which can really help to find out how much investment you need to do insulation. I have recommendation for company which I have used in past. Check it here.
I figure I'm gonna get what I get. It's gonna be about 13-15 in the walls with 2x4-size batts and maybe R-30 or so with blown in the "attic" part (half of the ceiling). I spent $250 on the spray foam kit and I'm not buying another kit. It'll be about R-15 to 20 in the vaulted portion of the ceiling (the other half of the ceiling). I can get about 2.5 inches with the amount of spray foam I have that's about 6 R value per inch. Code isn't gonna happen with what I have to work with as far as the existing structure. If I do a decent job of sealing off gaps with "Great Stuff", that'll be the best I can do. Something is better than nothing. This is a remodel from hell, so just finishing it and making it look good will be a huge accomplishment.

Doing a good job of drywalling will be a huge accomplishment in and of itself. It will involve a 4x8 sheet of quarter inch plywood and another 1/8 inch plywood sheet just to cut shims for the studs and not make it wavy. The existing framing is really bad.

It's a 70-year old garage that the previous owner did an awful job of working on, so we have old building and bad work to contend with. Prepping for drywall has taken about 6 weekend warrior days and we're not done yet.
 
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