Dense packed cellulose, Intello, and strapping
This is a variation on the dense-packed cellulose (DPC) bulging issue. I read this article and the comments. https://www.greenbuildingadvisor.com/article/considerations-when-insulating-with-dense-pack-cellulose and note several posters mentioned Intello. When you put DPC behind Intello, and then strap it, say with 1×3 strapping, is it not possible to be puncturing the Intello with standard 1 1/4 drywall screws?
My current wall assembly is (Outside to in): Clapboards, Hydrogap, pine board sheathing with gaps filled with closed-cell foam, 4×4 balloon framed studs, furred out with 2×3 placed horizontally to create a 5.5 inch cavity for the DPC, Intello, then 1×3 strapping. This seemed like a good idea at the time, but now wondering about the puncture issue with the Intello.
If I am to avoid puncturing the Intello, I either use 1 inch sheet rock screws–not ideal but it is on walls not ceilings? I use 5/8 sheetrock on exterior walls and rafter bays? (One of the whole points of strapping was to avoid the 5/8 sheetrock extra cost and weight? Not sure if I can accept small, hopefully, self sealing punctures in my Intello. or ??? I suppose where the strapping crosses the 2×3 furring I could use longer screws? Then the Intello is punctured between two wood pieces–better?
Any thoughts appreciated.
Thanks
Brad
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Replies
Puncturing the Intello is fine; the penetrations will be sealed by pressure between the layers, and for vapor-permeance it's the percentage of the area that's covered that matters. If you're going for an ultra-airtight building, you might lose a bit with the screw punctures, but not enough to matter in the real world.
Michael,
Thanks so much for your reply. I am not trying to create an ultra-airtight structure. The house when I started had a leaking roof, water and mud in the basement, no insulation, no heating system and much of the structure was damaged with rot. I am pretty sure whatever I get out of the Intello will be an improvement. Clearly, I went off script from what the 475 folks recommend for retrofitting wood structures. That said, I think my variation will work, or at least I thought it would until I started contemplating the sheetrock screws.
To clarify, even in the areas where the Intello will not be sandwiched in between two pieces of wood, the system will work. If a 1 1/4" dry all screw slightly dimpled into the sheetrock goes through the sheet rock, the 3/4 inch strapping, and then puts a small puncture in Intello that is backed by the dense-packed cellulose, those tiny holes will be insignificant? That would be great. I was starting to think I might have to use 5/8" sheetrock on my exterior walls.
Thanks again,
Brad