Deep energy retrofit — Envelope upgrade questions
We are well into the process of a deep energy retrofit for our 2,700 sq. ft. house in NYC suburbs, zone 4/5A. The house is a typical 1988 contemporary with 2×6″ wood frame construction, builder grade, sloppy subs, code minimum and 25 years of neglect. Long story short, we are currently replacing the roof, windows, doors, siding and HVAC. Before we started renovations, the blower door test result of just under 11 ACH50, proved that the envelope could be improved, so that is now our focus.
So far, all of the roof work is complete. The entire roof deck has closed cell SPF of R-38 in the joist bays and attic gable walls. The attic is now sealed (A/C & ERV ductwork, mechanicals are in attic).
We are now gearing up for the windows, doors, siding, envelope upgrades and I’m getting lost in my own head trying to figure out the wall details. The windows have already been ordered. They are VEKA finless Euro style tilt & turn or fixed, uPVC window.
The current wall is:
R-19 kraft-faced fiberglass
3/4″ cedar vertical shiplap
The upgraded wall will be:
R-19 kraft-faced fiberglass (walls where drywall needs replacing will be upgraded to R-21 Roxul)
WRB – Blueskin VP 100
1.5″ XPS (max thickness I can use due to overhangs)
Horizontal vinyl siding
The things I’m getting hung up on:
The position and type of the WRB as it pertains to air sealing and weather proofing
The taping of seams – plywood, WRB, foam
The window install detail
My current idea is to picture frame the ROs with 2×3, install the WRB wrapping over the 2x into the ROs. Then installing the 1.5″ foam, flashing from the foam into the ROs with membrane tapes (Extoseal, Wigluv, Vana, etc.). The windows would be installed flush to the exterior. Gap sealed with expanding foam tape, interior and exterior sealed to membrane flashing with tape (Corvum, Profil). Siding trim would cover the exterior tape and window/trim joints would be caulked.
Is my wall detail acceptable? Is there a better way to do it?
Should I tape the plywood or foam seams for airsealing?
Should I use a different WRB? I was thinking something like Hydrogap might be a better drainage plane behind the XPS.
Any other suggestions or criticisms are very much welcome. It seems to me, the more I read and research, the more confusing it gets. Getting the best performance while trying to stay within a reasonable budget seems to be a pretty difficult balancing act.
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