Downsides to Zip R-sheathing over existing board sheathing?
As part of an addition/renovation of my 100 year old colonial style home in NJ, I will be taking the existing portion of the structure down to the existing board sheathing as well as replacing all windows. I will be having cellulose blown into the existing balloon framed cavities from the outside.
My original plan was to then cover the board sheathing in a self-adhered WRB–either Henry Blueskin VP100 or Pro Clima Adhero. I am now considering putting Zip R-sheathing (thickness TBD) over the existing sheathing, to match what I’m using for the addition.
The question: Are there any downsides I should consider with having a second sheathing layer? Window opening depths are a non issue since I’m replacing them (with new construction windows) anyway, and replacing all jamb extensions.
I am ruling out removing the existing board sheathing. I have already scope crept the project enough that I don’t want to add another demo step, nor do I want to play structural Jenga and try to keep the existing structure braced properly while there’s no sheathing on it.
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