Please advise: Polyiso exterior in mixed humid coastal climate
This site is wonderful…and I’m hoping I can get some of you to weigh in on the wall assembly we are designing for an upfit of a really old single wide trailer at the coast. I’m wondering about the polyiso and how warm humid air on the inside dries out during the winter.
# Proposed Wall Assembly
Based on all our reading and research, here’s what we’re thinking for an exterior wall assembly.
* Interior finish: 1/4″ plywood paneling, painted with non-vapor barrier paint, then
* R-6 ecobatt insulation, compressed in-between the 2×2 studs and puffing out between 1×4 nailers, then
* 1/2″ polyiso foam exterior-facing foil-lined sheets as a continuous sheath (air/vapor/thermal barrier), then
* 3/8″ coroplast / air gap (rain screen), then
* 1/2″ LP Smart Siding panels (back-primed, structural siding) as the final layer.
What are we missing? What could be done better?
Here are some additional details that might help understand the context.
Thanks in advance for your feedback!!!!
# Climate Conditions
HUMIDITY & DEW POINT
Relative humidity 50% – 93%, rarely <30% or up to 100% Driest mid Feb; relative humidity <61% three days out of four Most humid late Sept: >89% three days out of four.
Dew point typically 28°F – 76°F, rarely <12°F or >79°F
Early Mar – Mid May and early Oct to mid Dec are most comfortable
Typically 36°F – 85°F, rarely <26°F or >89°F
Warm season late May – late Sept, average high temperature > 79°F
Cold season early Dec – early March, average high temperature <59°F RAIN Warm season 42% chance precipitation on a given day (49% thunderstorms, 20% heavy rain, 19% light rain, 12% moderate rain). Cold season 34% chance precipitation on a given day (35% light rain, 28% moderate rain, 26% heavy rain, 6% thunderstorms). Hurricane season Jun – Nov
# Current Construction Situation
Single-wide trailer with 2×2 framing. Has been gutted down to studs and retrofitted with hurricane straps. Currently, we have:
* Floors: Plywood, R-19 ecobatt insulation, enclosed cinderblock crawl space
* Ceiling: 1/2″ gypsum, R-19 ecobatt insulation, old metal roof, R-13 rigid foam, new metal roof
* Walls: 1/4″ plywood paneling, studs, 1×4 horizontal nailers, corrugated aluminum siding
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