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 Detail Library
A collection of one thousand construction details organized by climate and house part
Search and download construction details
Replies
anyone?
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.
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?