How to Build a Sill Plate

Stretch a chalk line along one wall from corner to corner along the outside edge of the slab, 1/8 inch from the edge. Lift the line and let it go to snap a chalk line on the slab. Repeat this for one adjoining wall.

Measure along the chalk lines and make a mark at 3 feet on one line, and at 4 feet on the other. Measure between the marks — the distance should measure 5 feet if the two lines are square to each other. Make adjustments to the chalk lines if necessary. Add additional chalk lines extending from the first two and square them using the 3-4-5 method described here.

Lay a 2-by-4 on the slab on the inside of the bolts. Place the end 1/8 inch from the end of the slab. Mark the location of each bolt that protrudes from the slab on the 2-by-4, then measure the distance from the chalk line to each bolt and transfer that measurement onto the 2-by-4. For example, if the bolt is 1 1/4 inches from the line, mark the 2-by-4 at 1 1/4 inches from the edge. Note: If you're building on a foundation wall and not a slab, place the 2-by-4 flush with the end of the wall, and add 1/8 inch to the bolt-to-line measurements so the resulting sill plate is flush with the foundation wall edge.

Drill holes in the 2-by-4 at the marks for the bolts. Remove all the nuts and washers from the bolts. Roll out the 1/4-inch foam insulation, and place it over the bolts with the edge even with the outside edge of the slab or foundation. Push the foam down on the bolts. Place the 2-by-4 over the bolts and repeat Steps 3 and 4 for each side of the slab or foundation.

Measure 3 feet along one 2-by-4 from the end, and 4 feet along an adjoining 2-by-4 from the end. Mark each 2-by-4, and measure between the marks to ensure that the two pieces of lumber are square to each other; the marks should be 5 feet apart. Make adjustments to reposition the 2-by-4s if necessary.

Place a washer over each bolt and screw the nuts on clockwise. Tighten the nuts with a box end wrench or socket.