Remodeling of our 100+ year old house (in southern Wisconsin) is proceeding well, including the new superinsulated sidewall assembly. We adapted new construction practices outlined in a VERY useful Building Science Corp. technical report on exterior insulation techniques to this remodel. Our GC, A Better Home, did a masterful job (in my humble opinion!) of building out the 21st century construction techniques we designed for this 1912 story-and-a-half house.
After we stripped the siding, ABH bucked out all the openings and added 3 1/2 inches of polyiso foam outside the old 1x sheathing. Combined with the existing dense-pack cellulose in the 2x4 cavity wall, the result is a functional sidewall R-value of 40. The furring strips that lock the foam to the sheathing also create a full pressure-equalized rainscreen cavity. If there is a building on our block that is basically immune from rot/mold/moisture problems, this is that house! Energy models indicate that the wall retrofit reduces the space heating consumption to half of the pre-retrofit condition.
I can't wait to get interior details completed so I can throw a blower door in and see what the infiltration looks like. The goal is 1,000 CFM50, which would put us at about 0.2 ACHn.
If you'd like to learn more, Jeff A and I will be presenting on this project at the Better Buildings, Better Business conference in March, at Wisconsin Dells. Come see us at: Bringing a 100 year Old Home to the 21st Century -- Thursday, March 3 at 3:15-4:30 PM
Don - thanks for the additional detail and design info. I do understand cost decisions (there is a current blog on Fine Homebuilding that speaks directly to that decision) and also wonder if ANY current mechanical devices have the longevity desired. I have seen Cor-a-vent and it looks fine for between the battens, but I was wondering about the possible termite/ant pathway behind your foundation's foam sheathing. What's to keep the little critters from going right up your wall?
Tyvek (tm) air barrier is sealed to the concrete and run up onto the sheathing before the foundation foam goes in. Then a z-flashing sits right on top of the foundation insulation, and is taped into the Tyvek. .
And, this is Wisconsin. It's cold enough that termites are not a problem -- at least not at the current state of global climate change...
As I mentioned in another forum, the foil vapor retarder (covering the insulation) on the exterior of the building could be a problem in some instances - - especially with any type of interior vapor retarder (paint, foil, etc.). While you may have well addressed that issue with your specific application, my concern is that others seeing what you have done try to duplicate your efforts but don't address that dual vapor retarder issue.
Regardless, nice looking work!
Correct -- for cold climates. That's why this REMOTE system is ideal for retrofit in OLD cold-climate houses, and for new construction anywhere. The key is that the sheathing (the outermost wood layer) is the "break point." The sheathing, and everything inside the sheathing, needs to stay above dewpoint and needs to be able to dry to the inside. Al materials outboard of the sheathing dry outward.
This particular house has multiple layers of oil-based interior paint, so the field of the interior wall is about as non-permeable as one can get. But we purposely did NOT air seal interior penetrations - the wall is dense-packed, so air cycling is limited, but there is still room for small amounts of moisture to dry inward in winter. .
But you are right -- houses built from the 70s to today in in cold climates could end up with a double vapor barrier configuration if retrofitted this way. And that COULD get pretty ugly.
I don't know if I can edit the original post -- do you think I should??
Great response as I was sure that you had properly dealt with the issue. Perhaps just posting your response to me would help to keep others out of trouble - - minus "I don't know if I can edit the original post -- do you think I should??"