Insulation retrofit

I have a short living room wall (4'tall) in my split level exposed to garage and thus to outside temps. Would like to insulate at lowest possible cost. Looking into injected foam, way too expensive and the material is not economically available for DIY. I have seen, on this old house, contractors drill holes near the top of walls between each stud and fill with cellulose, blown in. Sounds crazy, but what about this: Drill same kind of holes, then slowly fill with popcorn packing material, NOT the water soluble kind. Free material, shipped to me all the time. Should last forever. Any drawbacks anyone can think of? Is this stuff particularly flamable, so not suitable? I could also apply foam board to the outside of the sheetrock (garage side) and cover that with plywood, but with that air space between the studs, I'm not sure this would do any good. If I can get even r-10 or so, I'll be happy. Any advice would be much appreciated.
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first thought is that you wouldn't be able to pack it tight enought to do any good unless you shredded it, but then, you'd need a helluva lot of the stuff.

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Not flammable in that it is going to explode or spontaneously combust, but it does not meet building codes unless it is a modified material with a flame retardant additive. I'd not use it.

Polystyrene foam board is R4 per inch. It will help to do it that way. Plywood may not meet code, but sheetrock will.
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Edwin Pawlowski wrote:

Blueboard at 1 1/2" is R-7.
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snipped-for-privacy@yahoo.com wrote:

If your idea really worked well, don't you think they would do it commercially?
Unless the packing material is certified for construction use, it is likely to be against your local building code and a hazard if you have a fire.
There is a right way and wrong way for every job. I think you found one.
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The do, sort of. But only modified grade material is used. Bloc Fil in Portland CT is one company that I know of that does this. The material is ground finer that the packing material so it will flow better. The packing material is shaped so that it will hold something in place in a carton and thus, it will not flow into a cavity as well as a more granular shape.
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Why not just cut out the sheetrock on the garage side, insulate with fiberglass batts and then replace the sheetrock, tape & mud? It won't matter much what the garage wall ends up looking like. snipped-for-privacy@aol.com
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building codes usually require gypsum board on walls between an attached garage and a living area due to the fire resistant qualities of gypsum board; thus, the plywood and foamboard on the garage side would be violative
likewise, the popcorn packing material you mention is probably combustible and would be violative (it may even light with a match and stay lit, worse than being just combustible)
the least expensive and best bets are probably: 1. blowing (fire retardant) cellulose into the wall 2. or removing the drywall (may be easier from garage side) and installing fiberglass (bats, etc.) within the wall; recommend you ensure there are no air leaks leading to either the inside or the garage anywhere in the wall if fiberglass is used, including around electrical wall outlets, noting fiberglass is carcinogenic and cellulose isn't
with either one you should be able to easily attain the r-10 insulation factor you desire
a vapor barrier might also supplement the insulating qualities of your walls, and can be achieved to some degree with vapor barrier paints; not knowing all of the variables at play here can't suggest or not suggest additional coats of paint on the walls in your application (usually recommended against in hot humid areas and recommended everywhere else)
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