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Community and Q&A

Vented Attic vs Spray Foamed Rafters

nynick | Posted in Energy Efficiency and Durability on

The CC Spray Foam quote came in for the whole house and my God, it’s high. Part of the quote was over spraying the 6″ rafters in my attics to take care of thermal bridging. 

But two of my attics are already vented. I suggested we keep them so, but with proper baffles, air sealing and insulation values with new insulation. If we go this route and with budget in mind, should we use blown in cellulose and/or rock wool or FG batts laid perpendicular to each other stacked to attain the proper R-Value?

My GC hates cellulose but he’s not paying the bills. ; )


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  1. Expert Member
    BILL WICHERS | | #1

    Spray foam adds a lot of cost and often doesn't really gain you much, if anything, over other insulating materials. I generally only recommend spray foam for unvented cathedral ceilings, irregulator (cut stone, etc.) foundation walls, and some rim joist assemblies. For walls and attic floors, there are cheaper ways to insulate that work just as well.

    I'd recommend you air seal the attic floor the old fashioned way, with caulk and canned foam, then put in baffles at the eaves and blow in at least R49 worth of cellulose. That's cheapest way to go, and it will be one of the best performing too. It doesn't cost much more to go up to R60, so I'd consider that as an upgrade here.

    Get your GC a dust mask and tell him to go install cellulose for you :-)


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