Is spray foam insulation that much better than fiberglass?

SPS-1

... but all spray foams are not created equal. There are open cell spray foams, closed cell, low density, high density, water based, polyurethane,........... etc I have not priced spray foam, but I expect, like most things, the cheap stuff is not so good

Bob, when you suggest sprayfoam for the garage ceiling, I expect you are suggesting something like a high density, closed cell polyurethane. Is that right ?

steveel

Dope. I misread. I see now you DO have living space above garage.

If it were my garage, based on what I know, I'd look behind the panels. If it's insulated in there then what's the problem with that space? It might lack air sealing between the joists, where the joist bay meet the exterior walls but that would be easily fixed with blocks of that pink foam board glued in place between the joists with that GreatStuff blowfoam. It its not insulated between the joists, then I'd still use that pink foam board between the joists where the joist bays meet the exterior wall, glued in place with some GreatStuff blowfoam, and then I'd put up UNFACED batts of the insulation of your choice provided its approvied by your inspector for fire issues related to attached garages. I see no reason to blow foam in the garage. I assume you're not running your car in there in the winter to warm up right? You have the depth of the floor joists for new insulation, and its not exposed to much wind pressure so why not just use batts? More important to air seal the ends of the joist bays around the exterior walls, and then the walls and ceiling of the living space. Main reason I see to spray foam between the joists is to keep cold air from getting up into the living space from below, but iIf hot air doesn't go UP thru the ceiling/walls of the living space it won't be sucking cold air in from the garage so why not fix that problem from above?

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Also, does that duct need attention?

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Review your plan with your building inspector with attention to fire spreadhing issues due to attached garage.
SteveEl

concretemasonry

Use a litttle spray foam to seal cracks and corners and then blow cellulose into the ceiling a few inches above the top of the joists (or more since it will not raise the cost much) with cellulose and you will minimize the thermal short-circuiting of the wood joists that reduce the real R-values below what the pink panther says. It is far superior to fiberglass and does not hold moisture that can cut the insulating value in half.

Dick

steveel

The living space's floor would be in the way, and properly installed cellulose stays wet much longer than properly installed fiberglass of the same R value (of course if they are properly installed, for them to get wet in the first place would require something unexpected).