How to Replace a Floor Sill

A floor sill is construction-grade lumber that is bolted to a residential foundation. It is a "connection point" between the concrete foundation and a plywood subfloor. In general, floor sills are placed on a gasket, which prevents moisture from creeping into the wood sill from the foundation. Over time, a floor can feel uneven and might sag. This either is the plywood subfloor or the floor sill underneath. Repairing a floor sill means replacing it once you have pulled up part of the plywood subfloor to expose it.

Work gloves
Safety glasses
Impact wrench
Pry bar
Hand-sledge
Reciprocating saw
Tape measure
2-by-4-inch lumber
Pencil
Circular saw
Bolts

Instructions

- 1
  Put on work gloves and safety glasses before attempting to remove the floor sill.
- 2
  Unfasten the retaining bolts securing the floor sill to the foundation using an impact wrench, then set the bolts aside to reuse if they are in good condition.
- 3
  Pry up the old damaged floor sill with a pry bar. Use a hand-sledge to knock it free, if necessary. Cut the floor sill out with a reciprocating saw if you are unable to pry and/or hammer it out. Leave the gasket connected to the foundation for reuse.
- 4
  Measure the space for the intact floor sill using a tape measure, then measure and mark a piece of 2-by-4-inch lumber with a pencil.
- 5
  Cut the 2-by-4-inch lumber to size with a circular saw.
- 6
  Fit the replacement 2-by-4-inch lumber floor sill into place, then bolt it to the foundation with an impact wrench. Use the old bolts if in good condition or use new bolts if needed. Next, replace the plywood floor to finish the repair.

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