GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

What to do with rotten sill plate?

aberrant | Posted in General Questions on

In the middle of finishing my basement and I was cleaning up excess mortar around the sill plate (4×6) and I discovered about a 4ft section of sill plate that’s rotten, the worst of it concetrated in the middle of the section where up to an inch of the plate looks to be rotted out. I carved out all the rot I could with a screw driver to assess how deep the rot went.

Is it best to replace this 4ft section with new PT lumber with a sill plate? Does it look like there’s enough of the plate to put some EDPM under what remains and use non-shrink grout?

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. walta100 | | #1

    To me it seems like you need to understand why the wood rotted away before you repair the damage.
    What is the exterior grade like? You would want the wood to be several inches above grade and you don’t want water splashing on the ground near the wood.

    Today the wood sill plate would not be in direct contact with the concrete and the sill would be treated lumber.

    1. andy_ | | #3

      I think what you meant to say was the dirt level should be several inches below the wood. And sloping away from the foundation so that water won't pool at the wall.
      But yes, this is all about water management. If it's not water near the ground then it could be coming down the outside wall through a poorly detailed intersection like a window.
      Once the water is stopped, then you can look at repair. This doesn't seem too bad compared to a lot of the ones I've come across so you might be able to get away with a less invasive repair technique rather than jacking and replacing the sill.

  2. Expert Member


    As long as there is a fair amount of good wood left, I would dig out the rot as best I could, coat that section with wood preservative, add shims protected by strips of impermeable membrane under each joist for bearing, and fill the rest of the void underneath with spray foam.

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |