Following up tiny house & vapor retarder question
My partner and I are also building a “tiny house on a trailer” nearby in Northern Vermont and also want to use v-joint tongue & groove hemlock to panel the interior walls and cathedral ceiling (we may instead use white cedar T& G in the bathroom, nailed on strapping). I’ll leave out the floor (which in this case we’re treating like a wall) for the purposes of this discussion.
1) We plan to follow “tight building” practice/technique. Therefore, we need a layer of something on the warm side of the wall/ceiling underneath the T&G to act as both an airbarrier and vapor retarder.
2) We’ll be using a rainscreen wall (heart redwood clapboards nailed on strapping) over 1″ of taped T&G un-faced XPS, over plywood sheathing, over reclaimed native 2X4 framing in the walls, and over store-bought 2X6’s in the roof framing.
3) We are unwilling for several reasons to install the paneling over taped and primed sheetrock as Mr. Riversong has suggested and we wonder if this “layer” really requires anything as fancy (and perhaps unproven/unknown) as Mr. Riversong’s suggestion of Certainteed’s “Membrain” polymide paper. I know Goretex begins to fail as soon as it gets dirty so I fear (maybe wrongly) the same lack of longterm durability from this recent newcomer high performance “fabric.”
I’d love to hear If any one has had success with this product.
I wonder too if it is more resitant to tearing during installation (when compared to Kraft-faced fiberglass batts) – similar to Tyvek maybe?
But what about the alternatives (if there are any). I’ve read (and reread) everything I can get my hands on from BSC but I regularly end up somewhat more confused than before I delved in. However, from my research, it seems that Kraft paper also has the characteristic of having a variable perm rating depending upon the relative humidity at any given time. So maybe carefully installed Kraft-faced fiberglass batts (caulked and errant holes taped) would solve both problems too.
Then, of course, there’s the issue of what’s “greenest”. IOW, which qualifying product features the lowest embodied energy, which off-gases the least and which is safest in a fire (non-toxic when burned). Since whatever we use is basically going inside the living space, this makes a difference. And before anyone pipes in, we can all agreee now that XPS is nasty stuff during its manufacture and when it burns. However, I do like the fact that it can someday be reused (we ourselves will be using reclaimed XPS on the cold side of the walls and roof, for what its worth).
I look forward to any and all replies. Thanks! 🙂
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