Just a quick question. I have been researching floor framing. I notice
it's common to set floor joists on 16" centers. Now, if you start
laying the subfloor plywood on the outside of the rim joist , the otger
side of the subfloor falls short of the joist. Where do you make up the
Thanks. Hope that makes sense.
The first joist is set 3/4 inch offset, e.g. 16" from the outer band
edge to the center of the first joist. The subsequent joists are on
16" centers from there.
For example, if you start measuring from the left, make your marks 3/4
inch back from the 16" center marks on your tape, and use those as the
"left" edge positions for the joists, and it should work out. If
you've not done this before, double check everything before you start
I've also heard of people nailing a 3/4" scrap on the outside of the
band and measuring 16" intervals from there.
Most tape measures have some optical indicator of where every 16" falls,
like color of the number. Start at the rim joist, find this color, move the
pencil back 3/4" and past 3/4", make marks there. If the tape measure is
long enough, make these marks until done. If you start at the outer edge of
the rim joist (like you're supposed to), the tape measure will not be in the
center of the rim joist. That's the reason for the 3/4" offset to make it
16" OC on the remaining joists.
Use a framing square marks at each of these marks downwards for positive
squareness especially if you have a cupped joist.
Bridge blocking is a good idea if the span is long enough. A bar clamp may
assist you well.
Do use tongue and groove plywood. Place the worst side down. Use a scrap
end (long side of the plywood) for beating, tongue or groove. Do not hit
the tongue or groove of the intended installed plywood directly with a
hammer. The scrap must be the opposite of the intended end of the plywood
you intend to bang on. Tongue / groove, or groove / tongue. I prefer a 4'
length of scrap, at least 6" wide.
Do use the proper adhesive on the floor joists just before laying each sheet
of plywood. Don't lay the adhesive until you're sure of the proper length
of plywood, cut it first. Then lay the adhesive.
Run the long side of the plywood parallel to the joist runs. Pop a
chalkline for reference to keep all square and straight for the first run of
plywood across all the joists.
Be sure the nail heads do not break the veneer surface of the plywood.
Otherwise, you're going to have creaking noise later on when walking on it.
Do put the crown side up on the joists. Heavy crown should be avoided. Do
not use twisted lumber. Do not use badly cupped lumber. Do use metal joist
hangers with the proper nails. Do treat the piers and so forth for
potential insect infestation prior to laying the plywood if this is your
The rim joist on the ends where the joist are nailed need a cap when done.
That is, the rim joist should be doubled up. Bear this in mind when laying
out. Put the cap on before laying the plywood or internal joists. For
purposes of this response, the outer cap is the rim joist when laying out
the pencil marks for the remaining joists. The joist hangers should be
installed before installing the joists, if you use these. Nail only one
side of the joist hangers here, install the joist, then nail up the other
side of the hanger. Badly twisted or cupped joists will show their faces
The rim joist should be not just setting on the piers, they should be bonded
in some fashion to the piers.
Finally, commonality of 16" OC is pertinent to the span and the lumber size
of the joist. May not be pertinent to your situation. 12" OC may be needed
Um .. no? The tongue and groove plywood I've seen has the
tongue/groove on the long edge. This should cross the joists, so that
when the tongue and groove are engaged, there is support between the
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