Upgrade to vented cathedral ceiling
Now that we’ve reached the conclusion that (in the current market) it will be more affordable to buy a resale and remodel/upgrade than to custom build and “do it right,” I’m reading the GBA advice from a different angle.
My current question deals with upgrading a vented cathedral roof assembly, a popular bit of poor construction judgment (in hindsight) that flourished here from about 1990 – 2003. My wife likes one of these houses: 4-sided brick, hip roof, 1 story, with a vented cathedral roof over the main living and dining areas (where the ceiling reaches about 20 ft.). The remaining roof above each end of the building is vented attic truss assembly.
From what I’ve seen, I anticipate that in the cathedral there will be about 6” of blown fiberglass and nothing else; I can see the soffit vents and ridge vent; perhaps (scissor) trusses were used but I won’t be sure till I pull a couple of the can lights. I’ll assume the soffits aren’t blocked …. The interior is finished with gypsum.
I want to air seal this inaccessible assembly and add insulation, but I’m not finding info on this reno situation. Since I have such height to work with:
Can I add rigid foam board to the cathedral on the interior ceiling? 3” of polyiso tape sealed with an added layer of gypsum (ADA) airsealed and screwed from the interior? Is a gypsum sandwich around RFB troublesome? Will the cart-before-the-horse airseal turn into a ‘hot mess’?
Or: Would it be better (for permeability) to add a 2x6 drop ceiling, densepak with cellulose (giving 12” total), and add the new layer of gypsum?
Or: Do I need to strip the old gypsum before adding insulation to get rid of the gypsum sandwich?
Or: Of course I wish the roof was unvented so I could add foam to the exterior, but I have trouble imagining a useful way of adding insulation to the exterior of this (vented) assembly.
If your answer is too long to explain, please point me at whatever I should read! And thanks in advance.
Posted Mon, 08/15/2011 - 11:35
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