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Retrofit caulk/tape seal exterior gap between sheathing and foundation

AScudder14 | Posted in Plans Review on

1910 Zone 5 balloon frame 2.5 story home. Looking for advice. 

We plan to have dense pack cellulose blown in spring when temps raise so we can safely remove vinyl siding without cracking it. Interior recently skimcoated with mesh so do not want more holes to fix. 

In the meantime to help with drafts and air leaks I would like to caulk exterior bottom edge of our t&g sheathing boards that lay over concrete foundation. I can see obvious gaps when I look with mirror. I have already caulked interior under baseboards and sealed around outlets. 

We cannot easily access interior basement stud bays since covered in plaster/lath and layer of 3/4 plywood. Plaster is lead painted so plan not to disturb interior.

Mud sill is directly on foundation without sill seal gasket or capillary break. Will sealing sheathing edge still allow drying of mud sill in case of water wicking? Foundation water issues have been addressed but still want to be smart. 

Would this be worth time and effort since we cannot seal every t&g joint? 

Debating between exterior polyurethane caulk better or a tape product like Siga. Poly caulk cheaper. Or acoustical caulk? Gaps vary greatly but I don’t think any are bigger than 0.5 inch. 

Is there a better way to do this that I’m missing? Minus any interior demo. 

Pics are looking from ground up to sky. Thanks for all the help, I spend countless hours on here learning.


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  1. user-2310254 | | #1


    I don't have input for you but can give your post a bump.

  2. Expert Member
    BILL WICHERS | | #2

    This is not an application where you want to consider acoustical caulk. Acoustical caulk doesn’t set up, it stays gooey forever. You need something that sets up.

    My guess is you won’t gain much sealing that bottom gap unless it’s either much bigger than the gaps between boards, or if there is some kind of air barrier behind the T and G sheathing.


  3. Jon_R | | #3

    Consider using a blower door (or equivalent) to find the areas most in need of air sealing.

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