How to Jack Up a Floor and Replace the Seal

Billy McCarley

Normally, foundation sills are intended to last for the life of the home. However, sometimes environmental conditions erode the wooden sills that are responsible for supporting your floor. These sills sit directly on top of the foundation wall and are attached with large bolts. Replacing these sills will require lifting your home's floor from its resting place, removing the old sill and replacing it with a new, treated wood product. This project can be completed in one to two days by the average do-it-yourself homeowner.

  1. Place a 4x4 timber beneath the floor joists and 24 inches away from the inside wall of your home's foundation. Use 4-inch wood screws to temporarily hold it against the bottom of the floor joists. You will remove this 4x4 after you have replaced the foundation sill.

  2. Position three 4-ton bottle jacks evenly across the length of the 4x4 timber and jack them up slowly. Have a helper keep a watch on the bottom of the floor joists where they rest on the foundation sill. When the floor joists have been lifted at least 1/2-inch off of the foundation sill, you may stop jacking.

  3. Cut the anchor bolts off that attach the foundation sill to the foundation. Place the blade of a reciprocating saw just over the top of the foundation sill where the bolt extends beyond the sill and cut it off. Don't cut off the entire bolt. You will re-thread a nut onto this bolt to reattach the new sill.Continue cutting the bolts off until you have removed all that secure the old sill.

  4. Pry the old sill away from the foundation with a pry bar. The old sill should be completely removed from beneath the floor joists. If you can get the sill up and over the cut bolts, then jack the floor up a little higher until you have enough space to remove the old sill.

  5. Cut a new treated 2x8 to the length of the old sill and pre-drill holes into the sill so that it will fit over the old bolts already in place on the foundation. Slide the new sill in place and over the bolts then add new nuts to fit the old bolts that were partially cut off. Re-tighten the nuts and allow the floor joists to rest back down onto the sill.