Houzz Logo Print

Sealing Sill Plate in Fully Cast-in Joists

Jesse Frank
3 years ago


I'm looking for advice on how to best seal the sill on a section of my South Dakota, 1978 home where the rim joist and sub flooring are fully cast-in, below the block foundation. Below are two pictures of the issue and a diagram (courtesy of that I hope better illustrates my dilemma. On the floors where the 2x6 framing meets the block foundation I get air/cold drafts into the living space along the exterior of the room; the drafts are evident coming through the carpet/LVP where the block is exposed (as in the pictures). The pictures are of an area I'm renovating near a fireplace, however the issue is throughout the room. From the areas I can see, the block cavities are filled with fiberglass insulation.

I had considered spray foam in any big gaps, caulk and Drylok (or similar) the top of the exposed block, but looking to see if any of you have tackled this before or ideas as I do not want to install plates/insulation that will effectively raise the floor height and require redoing the whole room(s) flooring.

Comments (3)