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


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

2×4 and 2×6 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 2×4 and 5 1/2″ for a 2×6. 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


(c) Mike Merisko www.sawkerfs.com