What wrap should be used with thicker rigid foam? What about moisture release?
Would housewrap be necessary if I had:
hardicolorplus plank siding
with closed cell r5 1 inch taped rigid panel under that
then T11 panel under that
then r13 batt under that
then painted 1/4 drywall on interior?
(I am about to insulate and hardiplank the exterior of my already t11 paneled walls)
If wrap required what type/permeability would be required of housewrap and placed where? I am confused about trapping moisture not letting it escape, yet others have written that the tape on rigid board seams peel away and that rigid board shrinks exposing seam gaps over years, so leaving me to think taped closed cell may not remain moisture proof from outside. Reno Nevada, zone 5
I’ve read that with newer codes, foam rigid board that is thick enough for proper zone to not cause dewpoint issues, may also be too moisture resistant to allow the building to release moisture, so inspectors now allow not using wrap, yet the idea that tape fall off from rigid seams, and also that rigid shrinks and exposes seams makes me wonder if wrap should be used anyway. I’ll want to use rigid foam that is fire resistant i think that is the corning. Thanks for any help.
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Replies
Kelly,
Every wall needs a water-resistive barrier (WRB). A wide variety of housewrap products are available, any almost any of them will work for your project.
For more information, see:
All About Water-Resistive Barriers
Where Does the Housewrap Go?
There are some XPS products that are rated as WRB if detailed properly (mostly using twice as much tape on the horizontal seams by Z-flashing them with tape, but there are other details.) For the extra labor involved going with felt or housewrap (the wrinkly-crinkly kinds are best, if housewrap).
The XPS runs about 1 perm, housewraps run 8-50 perms, 15# felt is about 5max (lower when dry ), so the XPS would already be determining the drying rate toward the exterior.
R13 +5 meets IRC2009 code-min R-values for zone5 and R5 is at the absolute minimum IRC prescriptive R for insulating sheathing on 2x4 construction for zone 5 as well, but it works. A double-layer staggered seam approach using of 1" foil-faced iso (2" total) is easy to air seal, and would beat the code-min on whole-wall R by about 50% (for a 30% reduction in heat loss per square foot of wall.) And it would have less than 1% of the lifecycle greenhouse footprint of that 1" of XPS. Foil facers block all drying toward the exterior, but with 50% of the center cavity R outside the sheathing it has HUGE dew point margin in zone 5, and the interior can be kept fairly vapor open.