Detailing a Kneewall for Insulation Installation
Happy holidays, folks!
Updated Images Included!
We prototyped a bay of the attic insulation in our vented attic. Still nervous! Worried most about any condensation and moisture issues in Midwestern mixed climate.
Next up is tyvek on back of insulation? (Yes, we should have done that much sooner, but didn’t. We’re going to have to figure out how to reach over mineral wool.) So it will be tyvek on unconditioned vented side, mineral wool, intello membrane, service cavity, drywall. I suppose I like that it sounds vapor permeable for drying.
Does that sound okay? Can we staple the tyvek in? Is it necessary to tape over those staples in this situation where we really just need an air barrier? Does it have to be air tight for tyvek, or we can just block air flow as much as possible? I suppose I’m looking for a can’t hurt might help kind of possibility before we climb around all the trusses like acrobats. Around the trusses will be tough regardless. We don’t want to try moisture. We’re thinking about tyvek down to the cellulose, where the foam would start. But….there’s nothing down there to attach the tyvek to on the bottom.
Lastly, because it’s an attic, it has some weird spots. Does the intello HAVE to have a service cavity? Can it be right up against drywall in some spots where we don’t plan to puncture it?
Thanks so much for the confidence to proceed or feedback. 🙂
Take care out there.
Hello Folks, (I’m learning a lot lately, and have posted before but have a better understanding now of my issue. I would really appreciate any updated ideas as I may not have written it well previously.) We have a VERY tricky devil’s triangle in our 1.5-story earth-built home. The second story is our attic, it’s at almost ground level, a very steep roof, and 7-foot tall knee walls. The unconditioned triangle behind the knee walls has about 12-15 inch thick cellulose between the floor joists. Soffit vents are at floor level, we have site-built air chutes/baffles up to the upper attic above the ceiling where there are gable vents and an attic fan. (I can’t make the devil’s triangle a conditioned space right now. Maybe one day, but it’s out of my budget and ability currently.) The ceiling will have r60 Rockwool that is 14 inches thick, and the kneewalls will have r30 Rockwool that is 7 inches thick. We were going to use Intello from 475 on the whole space behind the drywall with a service cavity. We are in climate zone 4a, I believe. We get freezing winters with snow and humid, sweltering summers. This has led to a lot of worry about where to put an air/vapor barrier, and a wide variety of local contractors providing different advice. We’re hoping the Intello is a good choice behind the drywall. My big question that I hope doesn’t make me foolish: do the kneewalls need some sort of backing like OSB or foam board on the unconditioned side in our zone? Right now, we just have planned the unconditioned triangle soffit area, double studs and r30 Rockwool, then the Intello, service cavity, then the drywall. If the ceiling of an attic doesn’t need osb, does the kneewall? The ceiling of our first floor, which is insulated with the cellulose in the devil’s triangle, does not have osb or foam top or sealed barrier. There is cellulose completely filling the area between the first and second floor through every bay. Can I leave the kneewall insulation exposed on the back? I’ve been worried that trying to seal it off, and seal between the floor joists which are wildly interrupted with vents and ducts and electrical, will lead to leaks and trapped moisture issues during one season or the other. One insulation contractor told me we’re the only region that is wrong half the year whether we choose to put a barrier inside or outside because of the wild variety in weather. I can’t choose cold or warm climate, it’s both. I was hoping Intello would solve a lot of this problem for me. I would love to be more energy efficient, but I just really fear mold and moisture. We’re already earth built and doing our best to make green choices. We have planned mini splits to condition this space, it’s about 17×50 feet in size. What do I do about these kneewalls? I read several articles on here, but I didn’t see anything that felt like it works for this climate area. Is this an okay plan? Thanks so much, Sarah
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