GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

What water/air barriers in this roof assembly

Stolzberg | Posted in General Questions on

We’re thinking about replacing an old slate roof over gapped board sheathing and real 2×6 rafters in northwest MA (zone 5). With the following roof assembly, what affordable yet effective water/air barriers and/or underlayments would you use and where would you put them?  From the outside in we’re thinking:

1. Metal or synthetic slate (or asphalt shingles if need be)
2. 1/2 inch plywood
3. Vertical or diagonal 2x4s  laid flat to create vent cavities
4. 5.5 inches of polyiso rigid foam (2 layers taped)
5. Original board sheathing
6. Fiberglass batt insulation between 6″ rafters
7. Shiplap

I was thinking some sort of WRB between the board sheathing and rigid insulation and some sort of underlayment between the plywood and whatever roofing material we choose.  I was also thinking the WRB would serve as the air barrier plus taped foil faced polyiso as back up. Wondering what should be permeable and/or not permeable?   Thanks for any advice.

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.

Replies

Log in or create an account to post an answer.

Community

Recent Questions and Replies

  • |
  • |
  • |
  • |