Creating a Thermal Break
Hello again! After some time and lots of work since my last post, I’m writing again to request input from the GBA community.
This is for a PGH building envelope design on a renovation in the Catskills, NY (I’ll paste link to last post at end of this one).
The new roof is going on next week, along with new hemlock soffits and cut-outs in them for continuous soffit vents that will be installed.
A crucial and timely decision needs to occur ASAP related to this work: whether to add layer of exterior insulation and rain screen, to thermal break the studs in framing.
I have a quote from the builder who will do all the air sealing and building envelope execution, for the design in the attached PDF. You can see it has Steico wood fiber insulation at R7.5, also the rain screen, which would bump out the current exterior wall and affect location of soffit vent location.
This option provides a thermal break for the wall studs, but will add significant cost to the project. An alternative option is outlined below, achieving good R value, but no thermal break, as this one insulates from current walls inward.
Please note the floor joists will lack a thermal break. With the pier and beam crawl space, I could not find way to affordably condition the space or thermal break joists, so the resulting plan is to use 4″ closed cell HFO spray foam to R30
For the walls, here are the two option in mind, the first one being what is shown in the PDF drawing, the second one not shown in drawing, but quite similar, where rain screen and wood fiber are removed, adding a Tyvek or other material for some protection:
R39.13 w/ Thermal Break
From exterior: Board and Batten Cladding, Rain Screen, Steico Wood Fiber Insulation, Old Plywood Siding, Rockwool Bat, Air Barrier, Service Cavity with Mineral Wool Insulation, Drywall
R32.13 w/o Thermal Break
From exterior: Board and Batten Cladding, Tyvek (or equivalent), Old Plywood Siding, Rockwool Bat, Air Barrier, Service Cavity with Mineral Wool Insulation, Drywall
At the moment, I’m leaning towards “R32.13 w/o Thermal Break” option for two reasons:
1) The cost to thermal break walls is high, but still leaves the floors without thermal break. So it’s a lot of cost that still leaves inefficiency in floors. I can’t afford to thermal break both of them.
2) The cost savings from not making thermal break in walls can be applied towards solar panels, which ideally help make up or at least reduce the higher heating costs.
Here are some relevant numbers:
* Total cost for rain screen and R7.5 wood fiber insulation is $16K: rain screen $5K, Steico $6K, Steico labor $5K.
* Cost for solar panel installation (when including federal and state rebates): $20K
* Cost for labor and R23 Rockwool in 2X6 insulation: $5000
* Air sealing walls and ceiling: $6000 (foam in joists would seal floor)
* Cost for service cavity: $5000
* No cost yet for R9 mineral wool insulation in service cavity. A guess is $2500-4000 range.
I would appreciate input and advice! I’ve got a feeling, but also feel stumped, where maybe more experienced hands in this kind of situation can help.
There is the obvious, where not paying costs now to stop thermal bridging creates more cost over lifetime to heat the house. Here, I wonder if the plan to put money into solar is a smart one. I’m also wondering if the “R32.13 w/o Thermal Break” option would lead to moisture issues in Climate Zone 6, or would I be ok? The current house exterior siding seems pretty ok.
And fyi, here is my first post made on this project:
Thanks in advance for any thoughts and feedback!
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