How to Repair or Replace a Rotted Foundation Sill

The wood foundation sill, or sill plate, of a home installs against the concrete or cement foundation and serves as the base for the home’s structure.
Structural components, such as wall studs, attach to this sill plate for support. Though the location of a sill plate, a few inches above ground, helps keep moisture from damaging the plate, moisture does sometimes still penetrate and cause a foundation sill to rot. When this happens, the rotted wood should be repaired or replaced immediately to prevent further structural damage. Homeowners can handle some repairs. Widespread repairs or replacement need to be handled by professionals.

Step 1

Scrape over the rotted area of the foundation sill with a putty knife to remove the soft rot from the sill surface. Once you remove the soft rot, tap a putty knife into the wood around the rot with a hammer to dig into the wood by about an inch. Do this to create a rectangle shape around the rotted section and the chisel the wood out little by little with the putty knife and hammer to remove the entire rectangle.

Step 2

Measure the depth, height and width of the empty space in the wood. Cut a block of wood of this size out of a wood board. Apply a thin, even layer of wood preservative to the block of wood with a paintbrush and let the preservative fully dry.

Step 3

Cover the back of the piece of the block of wood with a thin, even layer of wood glue and put dots of wood glue around the edges. Press the block of wood into place in the sill and hold it for about five minutes until the glue adheres. Drive two wood nails through the wood and into the main section of the sill to further secure it.

Step 4

Remove all rotted sections of the rotted foundation sill. Cut down wood pieces, apply preservative to them and place them in the missing sections of wood to fully repair the seal.

Things You Will Need

  • Putty knife
  • Hammer
  • Measuring tape
  • Wood board
  • Saw
  • Wood preservative
  • Paintbrush
  • Wood glue
  • Wood nails


  • The repair or replacement of a rotted foundation still is best left to professionals. Though most homeowners can handle a small repair on their own, a professional can determine whether the entire sill plate is in need of repair or replacement. If the sill does need replacing, a professional also has more efficient means of securing the structure of the house so that no shifting or settling occurs during the replacement process.

About the Author

Alexis Lawrence is a freelance writer, filmmaker and photographer with extensive experience in digital video, book publishing and graphic design. An avid traveler, Lawrence has visited at least 10 cities on each inhabitable continent. She has attended several universities and holds a Bachelor of Science in English.