We need to insulate a garage that has 18 inch floor trusses (open trusses) for the story above the garage. The trusses are basically 2×4’s laid flat with 2×4 cross webbing. We want to use batt insulation (not decided yet on the exact amount yet). How is the best way to do a really good job of insulating this floor system?
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Any reason you couldn't do blown insulation?
Seems like it would be a lot easier. I don't know how you'd get batts into the trusses themselves...
Insulmesh the bottoms of the trusses and have fiberglass or cellulose blown in. THats what we do around here.
DOE energy star requires R-30 minimum stapled or tiger toothed so that the top of the insulation is in contact with the floor above.
Obviously I have considered blown in insulation, but the problem would be getting good insulation packing all over the area. The floor system is about 25x30 feet. I can't see how the blown insulation could get good coverage in that distance, in every section of the webbing. I guess we could cover small sections of the trusses, then blow some insulation, then cover another section...???
Also, would blown insulation be sufficient to fill the cavity to the top, without voids at the floor? As I understand it, the insulation should be in contact with the subfloor.
Edited 2/18/2007 10:03 am ET by ytek
Blown insulation is cheap. Staple mesh to the bottom of the trusses and fill 'em up with fiberglass. Nothing wrong with 18" of insulation when E-Star calls for 12" Just make sure the insulation goes all the way to the subfloor. A decent insulation company should be able to assure this. Michael
Two concerns...
First, I want to do the insulation job myself, so getting an insulation company will be out of the question (unless that is the only way).
Second, how can blown insulation fill all the nooks of the webs without blowing it back out? I don't mind filling 18 inches of insulation. It just seems like blown insulation would just blow back out when it starts to get full. Maybe I'm wrong. The only blown I've done is in attics where there is plenty of room to prevent the "blow-back".
That's what the mesh is for, it lets the air out but holds the insulation in. At least get a price from an insulation company. They buy the stuff so cheap that it generally amounts to getting it installed for free.
I started to do the same thing on my house. What I found was that the insulation company was going to throw in labor and was going to get it done even faster than I could do it for much less money. They buy insulation for half what you will pay.
See for yourself. Price buying the insulation yourself (don't forget sales tax and figure your time at $0 an hour) and compare that with a bid from a contractor that includes labor and installation.
You might ask them to price blown in and foam at the same time. Your cost for the insulation may not be too different than what they charge for doing foam.
"We want to use batt insulation ..... How is the best way to do a really good job of insulating this floor system?"
There is no way to get the best insulation job from batts. FG batts are your worst choice for insualtion.
As far as doing blown - you seem to misunderstand how it is installed. They staple up a mesh that hoplds the insulation in place while letting the iar out ahead of the fil. holes are slit here and there as needed to insert the hose. Any experienced ionstaller has no trouble filling to a good density so you do not have voids.
Either chpped FG BIBsystem or Cellulose.
an insulation company buys in bulk at wholesale so there is no way you can compete with them. They can do a better job for less money than if you rented the machine, bought the materials and blew it your self - don't forget hiring a helper and buying the stapler to put up the mesh.
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This is probably not an option because cost seems to be an issue, but for arguments sake I would suggest spray foam. We have used it in similar situations with great results. Also, have used foam to just do the perimeter joist bays, an area that typically is poorly done with bats.
I've used spray foam for much smaller areas, but this is a very large area and I'm sure cost would be prohibitive.
The only alternative that I can forsee is the blown insulation, but I still have a hard time believing that it would get full coverage, in all the tight spaces. Plus, how well will it hold up over the years, and not sag??
Spray foam is the only thing used in controlled atmosphere warehouses. As others have suggested..get some estimates.
I agree, over time I think blown would sag. Foam prices vary widely over North Amer., so at least get some prices.