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

Feedback on Masonry Wall Assemblies

art_kiwacz | Posted in General Questions on

Please share your thought on this. Its in Zone 5. Concern is exterior to interior R value ratio as well as inward vapor diffusion.

Have 2 options for wall assembly, which would you go with? Framing is done, windows are coming next week and this guy is having last minute doubts :0

Option 1:
Queen size Brick – 1″ gap – 1.5″ mineral wool (R6.3) – cdx with WRB (38 perm) – 2×6 with mineral wool (R23)

Option 2:
Modular Brick – 1.5″ gap – cdx with WRB (38 perm) – 2×6 with mineral wool (R23)

Would love to avoid things rotting 🙂

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.


  1. art_kiwacz | | #1


  2. Expert Member
    PETER G ENGLE PE | | #2

    For zone 5, both options leave the sheathing cold enough for condensation to occur in winter, so the sheathing will be getting wet unless you have a Class II vapor retarder or smart membrane on the inside (Table R702.7(3)). Your option 1 meets the 2021 IRC insulation requirement for R20 cavity insulation with R5 continuous. If you go with all cavity insulation, R30 is required, so your option 2 falls short. The vapor retarder will provide some resistance to inward vapor drive from the brick during warm weather, but I would still direct A/C vents away from walls to prevent direct chilling and stay away from vapor impermeable wall treatments.

    1. Expert Member


      Correct me if I'm wrong, but since it's mineral wool the normal rules on the insulation ratio do not apply, do they?

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |