Exterior wall retrofit
Hello, I rebuilt a 24 foot section of my home’s front wall a few years ago. The wall has 2or studs on 16 inch centers, 1/2 inch sheetrock inside, rockwool faced batts between the studs, 1/2 inch blackboard on exterior of studs, I then built a new 2×4 wall on 24 inch centers outside of the blackboard, fastened to 2×4 horizontal strapping , r13 unfaced insulation between those studs, 3/4 inch xps insulation board fastened over those studs with 2or horizontal strapping, and then vertical cypress board and batten. I have purchased 2 inch polyiso for exterior walls, and plan on using two layers of 2 inch on the roof. My question is, How much of this one wall that I built on the front should I remove? I plan on putting 1/2 inch Zip Sheathing, then the 2 inch polyiso, then 1×4 strapping, then my Cypress . Can I put the Zip Sheathing over the xps, then my polyiso, or should I remove everything back to the blackboard? And for the rest of the house, just a 2×4 studs wall with rockwool, and 1/2 blackboard. Can I leave the blackboard and put the Zip Sheathing right over it, and then my polyiso? Thanks
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Replies
HI Tommy.
It would be helpful to know where the house is located, but if you are planning to take the existing walls apart and plan to use ZIP sheathing and polyiso insualtion, it may make the most sense to take the assemblies back to the studs.
Use the ZIP for structural sheathing, water and air barrier, install the rigid foam as the exterior continuous thermal layer, then rainscreen details, and siding.
These articles will help to make sure you have the details right for your climate:
Walls that Work
Calculating the Minimum Thickness of Rigid Foam Sheathing
All About Rainscreens
Thanks Brian, That sounds like good advice. Would you recommend removing the 1/2x4x8 blackboard off of the studs as well, all the way down to 2x4 studs and the insulation batts between them? Thanks again
Hi Tommy.
I think that's a judgement call, based on it's condition and how much work you want to do. It may make it easier to install the ZIP to the framing in an airtight manner, and that would be a worthwhile reason to remove it.
Thanks Brian for your help . I'm going to remove everything down to the studs. Thanks again.