Homebuilding: Installing Sill Plates

When building a house, installing the sill plates correctly will determine how straight and square the finished product will be.

Hopefully the concrete contractor did his job and left you with a reasonably straight and square foundation. A good concrete contractor can make a framing contractors job of building a house a piece of cake. Even if the foundation is slightly out of square, a good framing contractor can adjust his sill plates and correct the problem.

When laying out the sill plates, snap chalk lines on the biggest square of the foundation. This will usually be the main part of the house. After snapping the front or back and one side, check for square. This is easily done by using the 3-4-5 method. Measuring 3' from the corner on the side, and 4' from the corner on the front or back. Make a pencil mark on the chalk line at these dimensions. Measure the distance between these two marks on the diagonal and if perfectly square will equal 5'. If it is not square, adjust the shortest of these two lines so that your measurement equals 5'.

Once squared these lines can be used as a reference point to square and keep parallel other sections of the houses foundation, like a garage or sunroom. By using the biggest square portion of the house, your work will be more accurate.

After your chalklines are all snapped, your ready to lay the sill sealer and sill plates. The sill sealer is put on top of the foundation wall first. This material comes in two forms. One is very similar to fiberglass wall insulation except thinner and with the same kraft paper backing. The other is a 1/4" foam similar to laminate flooring underlayment. Both materials come in widths to accommodate 2x4 and 2x6 sill plates. I prefer the foam sill sealer for its ease to work with and what I feel will keep drafts and moisture from penetrating under the sill plate better. Both sealers are installed butting up to the chalk line to the inside of the foundation wall. Both are pushed down over the anchor bolts till it pops through the sealer.

The exterior finish determines the placement of sill plates on the foundation wall. If the exterior finish is siding, the sill plates will finish flush with the outside of the foundation wall. In this case I like to measure in the width of my sill plate, 3 1/2" for a 2x4 and 5 1/2" for a 2x6. If the exterior finish is brick, the sill plate will be 4 1/2" from the outside edge of the foundation wall.

Holes must be drilled in the plates to install them over the anchor bolts. These 2x plates are usually required to be treated lumber to resist rot. To locate the bolt hole in the 2x, put the plate up against the anchor bolts. Using a speed square or a combination square, put the square on the edge of the 2x and against the anchor bolt. Hold your pencil against the squares edge with the lead 1/4" away from the blade of the square and draw a line. This will give you the center of the 1/2" anchor bolt along the length of the 2x plate. to get the center off the edge of the plate, measure from the chalkline to the center of the bolt. This will give you the location to drill the holes in the plate. Drill a 3/4" hole in the plate. This allows some wiggle room to drop the plate over the anchor bolts which are not always straight up and down.

Once the holes are drilled in the plate, bolt it down with a washer and hex nut. Continue the process by butting the next plate to the one just put down and locate the next set of holes, putting the sill sealer down ahead of the plates. Toe nail all joints where the plates butt one another.

This is an important step when building a new home. By installing the sill plates straight and square, it gives a solid reference to follow when framing the rest of the house.

(c) Mike Merisko www.sawkerfs.com

About the Author: Mike Merisko has been a carpenter for 26 years. Most of those years were spent in the homebuilding and remodeling industries. He was also in business as a carpentry and general contractor. While that is his forte, he also has experience in bridge building, commercial construction, and exhibit building which is how he earns his living these days. You can browse through articles by him and others at his website http://www.sawkerfs.com/ or visit his blog at http://www.sawkerfs.blogspot.com.