Definition
A sill plate (also called a mud sill) is the bottom horizontal member of a wall that sits directly on the foundation. It connects the wood framing to the concrete foundation through anchor bolts embedded in the concrete. Sill plates are typically pressure-treated lumber to resist moisture and insect damage. A sill sealer or gasket is placed between the sill plate and concrete to prevent air infiltration and moisture problems.
Formula
Standard anchor bolts are 1/2 inch diameter, embedded at least 7 inches into concrete, spaced maximum 6 feet apart. In high-wind or seismic zones, spacing may be reduced to 4 feet. Use washers and nuts to secure the sill plate. Replace any anchor bolts that are misaligned, corroded, or improperly placed before framing begins.
Example
Sill Plate Installation Example
For a 40-foot foundation wall with anchor bolts at 6 feet OC, place bolts at approximately 6-foot intervals along the wall. Use 2x6 pressure-treated lumber for the sill plate. Cut the sill plates to length, drill holes for the anchor bolts, place a sill sealer gasket on the foundation, then position and secure the sill plate with washers and nuts.