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What are good thermal break details on things like hose bibs, gas meters, and exterior lighting penetrations?

sfriedberg | Posted in Energy Efficiency and Durability on

In PERSIST/REMOTE wall construction with 4 to 6 inches of rigid foam outside the sheathing, furring strips over the foam, and siding attached to the furring strips, what are good ways to handle things like water pipe for faucets, natural gas supply lines, and metal electrical conduit penetrations? I don’t know how to provide a good thermal break consistent with mechanically strong (metal) piping, solidly attached to the structure, exposed to the elements on the exterior that punches right through to conditioned space on the other. Recommended techniques would be very welcome, as would “don’t do it this way!” cautions.

If it matters, assume the 2×4 framed wall cavities inside the sheathing are either uninsulated (zone 4 marine) or have simple R-13 fiberglass batts.

Somewhat related question: What mounting provisions need to be made for things like electrical service meter boxes (on the large side) and telephone NIT or cable drop boxes (on the small side). Relying on the siding to provide mechanical support is a non-starter, and many installers will have no idea how to deal with a rainscreen gap and 4-6″ of foam under the siding. I’ve reviewed the CCHRC REMOTE manual and its recommendation for wood mounting blocks for deck attachment, but that seems like overkill for many things (and impossible to arrange in advance for “the cable guy”).

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  1. sfriedberg | | #1

    Poking around, I found the similar question Brian Otten asked over at "Green building techniques" just a couple of weeks ago. I will pursue the references mentioned there, but still encourage additional suggestions as those reference focus primarily on the water barrier (drainage plane), and secondarily on the air barrier, rather than thermal breaks.

  2. charlie_sullivan | | #2

    For doing blocking without thermal bridging, a newly available material is a super-high-density EPS foam called compacfoam, imported by 475,

    It's much higher density than the highest density EPS or XPS otherwise available--the two densities available from 475 are 200 psi or 500 psi compressive strength, about an order of magnitude higher than high strength EPS or XPS. It will hold screws well. It's R-value is "only" 3-4 /inch, but that's 3-4 times higher than wood blocking. It's not as strong as solid wood, but it's plenty strong for holding miscellaneous little things. Also good for installing door and windows in thick walls without introducing thermal bridging. It's expensive compared to wood or ordinary foam, but might actually be cheap compared to some special mounting gizmo for a vent or hose bib.

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