Steel-sided, conventionally framed, closed-cell-foam-insulated home
I have been pondering building a low cost, high efficiency, low maintenance retirement home, and would like some input on my theoretical systems.
The structure would have conventionally framed, 2×6 walls, with no sheathing. In it’s place, would be diagonally place structural supports(2″ x 2″) spaced at 24″. In that 24″ space would be 2″ foam. The wall would than be strapped horizontally(2″ x 2″), and spaced at 24″ with foam in that space as well. The steel siding would then be installed, and attached to the horizontal strapping, and through to framing.
The stud cavity itself would then have either 1″ or 2″ installed with a 1″2 purposeful gap, and spray foamed in place.
Assuming that all needs are met regarding air and moisture handling, are there concerns regarding moisture collecting on the inside face of foam, in stud cavity, and causing longer term rot issue?
Other concerns?
MB
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Replies
M.B.,
This is a complicated assembly, without any advantages over the two most common ways of building a high-R wall (2x6 framing with exterior rigid foam, or a double-stud wall).
Here are some issues to consider:
1. You need to consult an engineer to make sure that your diagonal 2x2s provide adequate bracing.
2. I think you left out a word or two in this sentence: "The stud cavity itself would then have either 1 inch or 2 inches installed with a 1"2 purposeful gap, and spray foamed in place." Maybe you meant something like "The stud cavity itself would then have either 1 inch or 2 inches of rigid foam installed with a 1/2 inch purposeful gap, and spray foamed in place"?
3. If my guess on your missing words is correct, I would characterize this as a wall without sheathing, with opportunities for air leaks at all of the exterior foam joints, and with cut-and-cobble foam between the studs. This wall will take a long time to build, and could be quite leaky. What this wall cries out for is at least one layer of continuous rigid foam with taped seams. Two layers of continuous foam (without any 2x2s interrupting the foam), with staggered seams, would be even better.