Looking to insulate my garage(new construction) with a bonus room above.It’s a 3 bay garage approx.36’x26′(843 sq ft ceiling) 12′ ceilings 2×10 ceiling joist 2×4(585sq ft ) walls. Options are: #1:All open cell foam,#2: Closed cell foam 1-2″ then open cell foam the rest of the bays,#3:All dense pak,#4: Do it myself, I’m thinking of Handi Foaming 1″ Then dense pak cellulose the rest .I think I remember someone saying on this site a few years ago about putting up some 4×8 iso after dense paking then strapping,then the drywall(Mike Smith?)I looked in the archives but couldn’t find what I was looking for.#1 and #2 are between $3600-$5000 A little to rich for me.I’m leaning towards #4 or the iso.Anybody know if the Home Depot insulation machines will Dense Pak? any thoughts?
Thanks in advance
Greg
Replies
Here's what I did on a similar project
I am certainly not an insulatin expert, but I can share what I decided to do on a similar project (friends shop building, with an office/mancave in the attic), faced with the same decisions. I am sure some of the more knowledgeable folks here can get more specific, I will just share the process and results based on my observations.
We went with 3/4 inch R-Max (foil faced polycionate? ) on the outside over the plywood sheathing, and fiberglass batts in the stud cavities. The foam baord on the outside breaks the thermal bridge created by the studs, giving us about R 27 if I remember correctly, but we had 2x6 wall studs. We did 12" fiberglass (R38) in the ceiling and the floor of the office (plenty of space for this with the truss design). The walls in the attic/office area we put in 6 inch batts (R21) and a vapor barrier on the inside (this is in Montana). Then in any of the unconditioned areas above ceilings, we then blew in some cellulose to get up to R 49 total in those areas of the ceiling. It wasn't difficult to do ourselves, and it was pretty inexpensive compared to hiring a company to come and foam the whole thing. It is built on a concrete slab (thickened edge, slab on grade) with 2 inches of pink foam board on the outside and an inch of foam under the slab for the first 4 feet. all the way around. Lots of vents for the attic and lots of baffles to ensure air can get to all the areas created with attic trusses.
My friend has been VERY happy with his heating bills, so it must be pretty energy efficient. And he has never needed an air conditioner, so it is doing pretty well in the summer heat as well. We are in Montana, so remember that we have very dry air and only about a month to a month and a half where you would have any need for air conditioning. The first winter after construction he didn't have any heat in it, but the dog's water bowl never froze all winter long. The strategically placed windows and good insulation apparently allowed the winter sun to heat some of the slab and the insulation held that heat in nicely. And we live in an area where it can get 30-40 below zero.
Sorry it took awile to get back to you: I made up my mind .I'm going to do a 1" layer of foam,Dense pak ,Then 4x8 1"polyiso
The toughest part was finding the cellulose machine,got it covered though,so I'm good to go.
Thank You for the reply!
Greg
Wait - you are going to put closed cell foam, then celulose, then rigid foam board? That creates a double vapor barrier - a damaging situation where air vapor can't escape, so it builds and conenses against surfaces and causes rot and mold.