Homebuilding: Laying Tongue and Groove Plywood

You have just finished framing the first floor deck for a brand new
home and your ready to start putting down the 3/4" tongue and
groove plywood. If you framed it well and got your 16" centers
laid out right, the process should go smooth as silk. The key to
success is in the framing of the joists.

The first step in laying plywood over the floor joists is to snap
a chalk line. This gives you a straight line to follow. I always
snap this line at 48 1/4" in off the edge of the rim joist. This
ensures that in the course of installation the plywood (which is
48" wide) will not hang over the edge of the rim joist. It
doesn't matter whether you start in the front or back of the
house.
For best results, start where you have the longest run without a
jog in or out in the foundation.

After you have snapped your line, determine which joist the first
sheet of plywood will break. If the joists where laid out 16"
o.c. (on center) from the end of the building, the edge of the
plywood would split the joist at 8 feet. Sometimes the roof
layout determines the floor joist layout. This is usually the
case when the roof is a hip roof. In this instance start with the
joist that will allow the plywood to cover all the joists, even
if it hangs over the edge of the first joist. This will be cut
off later.

After you have determined where to start, apply construction
adhesive to the top edge of the joists. Apply no more than 48"
the width of the plywood. Lay the first sheet in the glue with
the groove edge on the chalk line. Holding the sheet to the line,
nail the leading edge of the plywood to the rim joist so it
splits the joist. You'll be covering 3/4 of an inch of the joist
with 3/4" exposed. Still holding the plywood to the chalk line,
put a nail in the rim joist at the first joist.
Now put nails in the rim joist where the floor joists are nailed
into it. When nailing off the field these nails can be used as a
guide to find the joists.

Now the groove edge can be nailed. On the leading edge, move the
joist so the edge of the plywood splits the joist. Once you have
the joist where you want it, nail the plywood to it. Now taking
your tape measure, hook the leading edge of the joist you just
nailed, and pull it along the edge of the plywood. Mark 16"
centers on the plywood and pull the leading edge of the joists to
this mark and nail them. This will help keep the joists in line
and will help make sure future course of plywood break on 16"
centers no matter which joist you start with.

Glue up the joists for the next sheet. Butt the next sheet to the
one previously installed, making sure to hold it to the chalk
line and nail the groove edge corner. Nail it to the rim joist
just like the first sheet. Once again move the joist so the
plywood splits it. Hook that joist with your tape, mark centers
and move the joists to the lines. Keep laying the plywood in this
fashion to the other end of the building.

Your now ready for the next course of plywood. If I've started
with a full 96" sheet on my first course, I like to start my
second row with a 48" piece. This works great if the building
length is in increments of 4 feet (24',28',32',36' etc.). This
isn't always the case. If the building is an odd length you can
usually use your ending cutoff to start the next course. Stagger
the joints a minimum of 32" apart.

Start the next course by gluing the joists. Do not apply the glue
more than 4' beyond the first course of plywood. Stand the sheet
on its tongue edge next to the groove edge of the sheet you are
standing on. Make sure its butt edge is lined up on the joist it
is breaking on and let it fall into the glue. As it hits the
glued up joists, step on it and try to pull it in with your foot.
Only under the right conditions will the tongue go completely
into the groove. Sometimes the sheet can be jumped into the
groove. This involves standing on the sheet and jump with force
towards the the sheets in the previous row. In most cases it
takes a sledgehammer and a 4' to 6' 2x4 beater block to persuade
the sheets together. The block keeps the groove edge from getting
damaged by the sledge. This is a two person operation. One stands
on the tongue edge of the plywood to guide the sheet into the
groove while the swings the sledgehammer. This will be the
process for the rest of the installation.

Once the piece is in place, nail off the tongue edge, making sure
the leading edge is breaking on a joist. Move the joist so the
groove edge breaks on the joist. Pull 16" centers from that
joist, mark the plywood, move the joists if necessary, and nail
them off.

To keep the joists at the ends of the building straight, do not
glue or nail them. Ideally we'd like the plywood to be hanging
over the ends. After all the plywood is in place, snap a line
from one corner to the other and cut this over hanging plywood
off. Move this joist to the cut edge to make it straight and nail
it off.

Tips:
-Field can be nailed as you go (recommended to set sheet in
glue)
or after all plywood is in place.
-do not glue more than 4' out from sheet. Keeps glue off your
tape
when you pull centers.
-When nailing groove edge, nail at least 2" from edge to keep
from
collapsing groove.
-Before installing plywood, check for damaged grooves and
tongues.

Mike Merisko (c) 2006
www.sawkerfs.com