November 01, 2009
Insulating Cathedral Ceilings
Codes aside, what is your opinion on dense-packing closed-vault roofs with fiberglass or cellulose? Yes, this means packing the entire cavity full so insulation is in contact with all six sides of the box—no more roof “ventilation.”
The issue? We come across closed vaults all the time that are insulated with filterglass—er, I mean fiberglass—batts. We see from infrared images that air moves easily through these cavities, degrading the effective R-value. Building science tells us we can get rid of roof ventilation if we add rigid foam over the roof deck—but this is expensive. Or we can rip off the drywall and spray closed-cell foam in from below—but this is also expensive. Both approaches control moisture migration by not allowing it, but these are not options for many clients with existing homes.
So if we control moisture in the home, have good airtight drywall, and dense-pack the cavity, isn’t this a decent option?
I mean, its got to control air and moisture and the danger of condensation more than the leaky fiberglass batts in there now, right? What are your thoughts?
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