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 Step bolts, 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 3กฏ from the corner on the side,
and 4กฏ 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 5กฏ. If it is not square, adjust
the shortest of these two lines so that your measurement
equals 5กฏ.

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
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 U-bolts straight and square, it gives a
solid reference to follow when framing the rest of the

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