BlackNBlue
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- May 11, 2016
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I'm doing a lot of research on how to layer my materials, and getting conflicting information, much of which makes assumptions that aren't true in my case. I'd like to hear from people who have experience with similar circumstances (materials and location).
My materials:
* Aluminum-bodied stepvan. Built fairly well, not quite airtight but nowhere near as airy as corrugated metal RV siding. It won't rust, so if I design a system that gets it wet, not a problem per se.
* Fiber/paper-faced (not foil-faced) 4" polyisocyanurate boards. This stuff is apparently much less effective when wet, unlike XPS.
* Some kind of heavy plastic sheeting.
* Adequate ventilation: floor vents, opening skylights, and probably extractor fans.
* Heat will initially be catalytic propane, to be mostly replaced by a woodstove in the not-too-distant future. I'm also looking into air-air heat exchangers.
Intended climates:
* Priority one is very cold/dry (Rocky Mountains in the winter).
* Priority two is cold/wet (PNW in the winter).
* Priority three is hot/dry (central California or Montana in the summer).
* Hot/wet will be rarely encountered; I'm willing to sacrifice suitability for this climate to optimize for the other three.
Do I place sheeting between the insulation and the alu skin? Then won't moisture from the inside condense on the sheeting and soak the insulation?
Or do I place it between interior plywood and the insulation? Then won't any moisture that does get to the insulation be trapped forever? Would drain holes help? I suspect not; that it has to breathe to get dry. An air space between the alu and the polyiso is not a good option because it takes up even more space, but I'll consider it if it works really well.
:huh:
My materials:
* Aluminum-bodied stepvan. Built fairly well, not quite airtight but nowhere near as airy as corrugated metal RV siding. It won't rust, so if I design a system that gets it wet, not a problem per se.
* Fiber/paper-faced (not foil-faced) 4" polyisocyanurate boards. This stuff is apparently much less effective when wet, unlike XPS.
* Some kind of heavy plastic sheeting.
* Adequate ventilation: floor vents, opening skylights, and probably extractor fans.
* Heat will initially be catalytic propane, to be mostly replaced by a woodstove in the not-too-distant future. I'm also looking into air-air heat exchangers.
Intended climates:
* Priority one is very cold/dry (Rocky Mountains in the winter).
* Priority two is cold/wet (PNW in the winter).
* Priority three is hot/dry (central California or Montana in the summer).
* Hot/wet will be rarely encountered; I'm willing to sacrifice suitability for this climate to optimize for the other three.
Do I place sheeting between the insulation and the alu skin? Then won't moisture from the inside condense on the sheeting and soak the insulation?
Or do I place it between interior plywood and the insulation? Then won't any moisture that does get to the insulation be trapped forever? Would drain holes help? I suspect not; that it has to breathe to get dry. An air space between the alu and the polyiso is not a good option because it takes up even more space, but I'll consider it if it works really well.
:huh: