choosing drain plain material or no drain plain at all
pakrat1
| Posted in General Discussion on
I have a problem about a decision.
houston tx, 16 foot tall wall 2×6 studs with Dense pack cellulose or open cell SPF, 1/2 plywood, ccw-705 P+S vapor closed, (probably should have used vapor open P+S, but too late to change, a drain plane just incase water gets behind foam, then foil faced polyiso taped at seams which will be the WRB, 1×4 strapping rainscreen, then Hardi lap siding. The space will be air conditioned and heated and have a dehumidifier and ERV
my question is choice for the drain plain.
option 1) 1/8″ waterway mesh vented at bottom (will I loose too much R value due to excessive air movement from chimney effect through any air leaks higher up the wall, no guarentee they will all be sealed)
option 2) drain wrap, or hydro gap, more restrictive to air movement.
option 3) forget drain plain, would water trapped between foam foil and P+S be a problem,
yes, I do realize that (In a perfect world) a good tape job on the outside of the foam-foil should prevent water from ever getting back there
I appreciate any help I can get, I have been stewing over this for way too long, but have been unable to get a definitive answer anywhere on GBA/ FHB / JLC
I am posting this on all three sites
Thanks Mike
PS pix shows bottom of wall and roofnado air block for waterway drainage path
Replies
PS I have studied "wrinkled-housewrap-behind-exterior-rigid-foam"
Can the CCW-705 move to the outside of the foam or is it already built?
already installed
Can you switch from polyiso to rockwool? Polyiso is acceptable below grade so it shouldn't be a problem installing it without a air gap, but two vapor closed layers in a wall makes me cringe.