I will soon be embarking on a project to gut my above-garage bedroom, and by the time I'm ready to put it all back together again will have to reinsulate. It's cathedral ceiling, which I'm guessing is currently insulated with fiberglass. I'll be re-roofing and adding a couple of dormers as part of the project.
I really like the look of the spray on foam and suspect it would be the best R rating which is pretty important here in MN. Before I speak to any contractors, has anyone out there tried a DIY foam insulation? Tiger Foam is the most prominent on the internet. It seems expensive, but I bet hiring a pro would be too. I also have visions of getting into a big mess with DIY.... Interested to hear of any experiences anyone here has had. From what I can see of the Tiger product, it's only really meant for the first inch, but combined with fiberglass that could be good enough. I really like the idea of the air and vapor seal it should provide.
I used a Tiger Foam kit to insulate my rim joist before finishing my basement. A few points to keep in mind.
The foam cans need to be warm, 70-80 is recommended. I had to warm them with a space heater.
You have to work fast. Stopping spraying for more than about 30-45 seconds will plug up the nozzle because the foam hardens in it. They are disposable, and they give you some extras, but if you have a big area and you don't keep moving you will use a lot of nozzles.
The hose on the kits is pretty short, so you will be moving the cans a lot. Best to have a helper moving the cans so you don't have to stop spraying.
It is very, very messy. Not so much when you are spraying, although there's a little backspray, but when you stop, foam continues to ooze out of the nozzle because it is expanding, and it drips on everything. Figure on wearing a disposable moon suit with a hood, and full face shield. It is extremely sticky and is hard to remove from anything, so cover everything you don't want foam on.
You can spray it as thick as you want, but have to do it in 2" thick passes, letting it expand and set a bit between passes. Do one rafter bay, then another, then go back and do a second layer on the first, etc.
The foam kits don't really contain all that much foam. I used the 300 board foot kit just for my rim joist. For a big roof and 4 or 6" thick foam you will need a bunch of them. The empty cans are considered hazardous waste in a lot of areas and have to be disposed of properly. Which reminds me..the cans have to be shipped by motor freight, hazardous class, so it's expensive and you have to be home to sign the release.
Now for the big issue. Cathedral ceilings usually need ventilation under the roof sheathing. If you are removing the drywall and foaming up against the roof sheathing you wont have any ventilation unless you build a double roof deck with venting in between (which is a good way to go, but the devil's in the details). If you are removing the roof sheathing as part of the re-roof and spraying down against the drywall, then you can maintain ventilation by not filling the bays fully. Unvented cathedral celings (hot roof) are becoming more common, but there are concerns with shingle warranties and a lot of codes don't allow them.
For a big job like yours, I'd really recommend a pro. They have bigger tanks of foam with heaters and longer hoses, also heated. I'll bet for a big job it won't be much, if any, more expensive.
I used the same kit to improve a distant bath underfloor insulation - our experience was uncannily similar. I was working in a crawlspace with very little room to maneuver - lugging those cans around was not easy.
Make sure you wear a disposable boiler suit, gloves, a cap and eye protection. The stuff is next to impossible to remove from skin & hair. The temps are critical - I was careful and I still ended up towards the end with a volume/mix difference with one can running low slightly before the other.
I have seen unvented cathedral roofs shingles cook and fail in 5-6 years, you need an airspace from bottom to top ridge vent, probably a second layer of sheeting just below the sheets that lay on the joists, the foam vent chutes you staple on under the roof deck might work if the foam doesnt compress them. Find out what is recommended and works.
How about the walls of an already constructed house? I hear they can do blown in by lifting the siding and drilling holes. How about spray foam? Good coverage?
For a large area I would call in a pro. I did a camper it it cost me $300. BTW one advantage of spray in foam that most people dont think about is that it adds a lot of structural integrity to a frame building. In my opinion this alone is worth the extra cost.
Thanks to all for responding. Some great advice there. I've decided to call in the pro's for this one. Will also look to add in some ventilation. Pretty sure there isn't any at the moment (there are certainly no soffit or ridge vents - but I will put them in now). I like the idea of the foam for rims - I have a few areas of my basement where I'm sure there either is no insulation on the or if there is, it's probably fallen away. The Tiger foam seems ideal for a small project like that.
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