Zip or Zip R?
I’ve been doing a lot of research trying to find the best option for residing by 1920 house located in Climate Zone 4 – mixed-humid. Existing plaster and lathe walls on the interior. I’ve asked a few questions on this website and the responses have been very helpful so I’m asking one more.
I’m planning to remove the existing vinyl siding and wood clapboards and spray foam the walls from the exterior with medium density spray foam to give the stud cavity an R value of about 21.5.
I’ve then debated using Zip sheathing or possibly Zip R to get an additional 3.6R and reduce thermal bridging and then a rainscreen under Boral Truexterior siding. My question is, Zip R has a vapor permeability of less than 1 perm – Zip sheathing has a vapor permeability of 12 – 16 perms.
Will the permeability matter since the spray foam is vapor permeable? Or do I need to allow the wall to dry in both directions (and will the existing plaster walls reduce drying to the interior?) Thanks
GBA Detail Library
A collection of one thousand construction details organized by climate and house part