Zone 7 Wall Design Review – Deep Winter Homestead
We are making a modest 25×28′ addition onto the 1bd/1ba cabin we live in, to convert it into a family home. The existing structure is 2×6 conventionally framed with R-21 fiberglass bats.
For the addition I am thinking of something like this:
2. MemBrain, Siga Majrex, or Intello vapor barrier with seams sealed with Siga tape and glued to electrical boxes, top plate, etc. with Tremco acoustical sealant.
3. T-Stud 24″ OC + BIBS -or- dense-packed cellulose
4. Steel strap bracing -or- OSB/plywood
5. 2” GPS Foam (R-10), foam-glued (PL 300 or similar) around sheet perimeter to the studs, and glued to each other on joints
6. Furring (1/2″ or 3/4″ plywood strips with Cor-A-Vent along bottom and top -or- a roll-out rain screen)
7. Vertical steel siding
We are re-siding and re-roofing the existing building too, so layers 5-7 will continue onto there to help make the whole building more consistently insulated.
1. it was suggested to me to use J-channel along bottom of wall to support the 2″ GPS and protect the exposed edge from pests. This seems to me like an invitation to hold water and rust the J-channel. Water will not be absorbed by the GPS, but it doesn’t seem like it would be good sitting there, either, if it found a way in.
2. A contractor mentioned to me a product which can be “rolled out” to serve as a rain screen/gap and integrated rain screen ventilation to keep pests out of the rain screen layer. I am picturing it being made out of a composite material, so I am not sure if siding could be fastened to this like we could do with plywood strips. What are your thoughts?
3. We aim not just to build an efficient home, but a healthy one. We always choose low/no-VOC products when available. We plan to use a CERV2 which detects and manages VOC. But reading about Tremco Acoustical Sealant, which I know is great stuff for air tightness, it contains distillates, petroleum, and mineral spirits. I am sure this is why it’s so useful, never cures, etc. But honestly if this would lead to months of off-gassing making my kids sick (regardless of how well the CERV2 might work) I’d rather have a drafty house. Thoughts?
4. Any concerns with steel strap bracing instead of sheathing? I like the openness of this wall, but also because we live in a forest, I am worried this would be asking for trouble from mice.
Thanks everybody! We are so fortunate to have this forum.
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