High performance home retrofit (Climate Zone 5)
I am a relatively new member of the GBA community but have been following high performance home techniques on GBA, Fine Homebuilding, etc for some time.
I am a builder in the Boston area and am now renovating my own home. After years of theoretical reading and discussion, I’m going for it and trying to do a whole house retrofit that is as efficient and environmentally friendly as possible. I have sort of glommed on to the idea/path of a Pretty Good Home.
R value targets are BSMT = R20 walls, 1st/2nd floor R32, Attic R60. Slab will be limited to R4-5.
A few questions for the group here are;
1 – Basement is an older junk slab, approx. 2″ thick over rubble and dirt. Walls are larger stone with somewhat smooth concrete skim coat on interior. A few hairline cracks visible. Lot drops of steadily front to back creating a full walk out basement. Front wall approx. 65% below grade, side walls less than 40% on average. Over the last 7 months, basement observed to be dry from both moisture penetration and condensation. With 8′ from slab to joists, I’ve decided to skip the repour and use EPS foam over the slab and walls. The basement will be finished so I plan to tape the EPS with a “european tape” and use a double plywood subfloor over the EPS as seen in several articles here. Questions on the basement assembly are;
* What type of EPS is best for this application? Unfaced, faced, best type of EPS?
* What type of plywood is “most stable” for this type of subfloor?
* Best adhesive for EPS to wall adherence?
* Short sighted not to add drainage to sump for an observed “very dry” basement?
2 – 1st and 2nd floors have been double studded to create an on average 8″ thick wall assembly. Plan is to use Intello inside, blown in cellulose in cavity, mix of old pine sheathing/new 1/2″ OSB on a dormer we added, an outside layer of SonoClimat ECO4 exterior insulation (R4) and finally a self adhered WRB that is TBD. Questions on wall assembly are;
* Can/should the Intello be added once all rough elec and plumbing are complete, then taped to seal? I’m assuming yes and realize this is probably a basic question but want to get it right.
* I plan to use the Intello as the netting for the cellulose. We don’t have room to loose another 3/4″ or 1.5″ for horizontal strapping over the Intello. Is this an acceptable method for install?
* Are specific air-sealing outlet boxes necessary or can you work around standard boxes by taping from the rear of boxes?
* A lot of hype around European WRBs. I have only used Henry Blueskin to date for a self-adhered WRB. At nearly 2.5 times the cost, are the “other” WRBs worth the cost? Brands to consider?
Attic to be blown in cellulose to 18-19″ thick. Slope of roof does cause a section of the roof of no more than 3′ to be limited to 11″ of cellulose. This obviously brings down the R value at this outside edge of the roofline. Not ideal, but we sistered rafters down as low as we could.
Currently the attic has two large gable vents (gable roof with front and rear shed dormers). I have read of some people not venting a blown in cellulose attic. Seems crazy, is that a thing? Only reason I ask is the reduced rafters are right where rafter baffles will have to go, further reducing R value in that section.
I appreciate any advice this knowledgable group is able to share.
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