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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 🙂

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Replies

  1. art_kiwacz | | #1

    anyone?

  2. Expert Member
    PETER Engle | | #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. kbentley57 | | #3

      Peter,

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

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