Zip R12 with Class III Vapor Retarder in Portland, ME Zone 6
![](https://secure.gravatar.com/avatar/c7ebe6f25bdd0dd09b94a213c05f1792?s=52&d=https%3A%2F%2Fimages.greenbuildingadvisor.com%2Fapp%2Favatars%2F200x200%2Fb.png&r=g)
Hey folks,
For our house in Portland ME, Zone 6, here is the wall assembly we are planning:
Cedar Clapboard Siding (unfinished)
Vertical Rainscreen
Zip R12
R23 Rockwool in 2×6 cavity
Sheetrock with latex paint
We are assuming we don’t need a vapor barrier on the inside of our wall given that we are above the R11.25 necessary to keep the sheathing dry. Is this sound?
thanks!
Brad
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
![](https://www.greenbuildingadvisor.com/app/themes/greenbuildingadvisor/dist/img/modules/detail-library/thumb1.png)
![](https://www.greenbuildingadvisor.com/app/themes/greenbuildingadvisor/dist/img/modules/detail-library/thumb2.png)
Replies
I don't have a response to share but will bump your question as I'm curious to hear the replies also!
thanks!
Yep, this meets the requirements shown in Table 2, derived from Table R 702.1 2018 International Residential Code. Okay, technically you're at 34%/66% instead of 35%/65%... but that doesn't really matter.
BSI-100: Hybrid Assemblies
https://www.buildingscience.com/documents/building-science-insights-newsletters/bsi-100-hybrid-assemblies