I am designing a new house. We will be using 12" engineered joists
with relatively short spans. The deflections on these alone calculate
to about 1/500 of the span. We will be using glued and screwed 3/4" ply
for the subfloor on top of that. I haven calculated that deflection,
but its got to be real small. Normally, the 3/4" hardwood floor would
run perpendicular to the joists. However, to do that would require a
framing direction that is much more expensive. Given that the floor is
so stiff, can we run the flooring parallel to the joists - or is that a
I would think it was a "never" rule, unless the flooring is _extremely_
stiff. Remember that any floor flex in this case will tend to open and
close the inter-board spacing. Ie: cracking any finish. Allowing dust
into the cracks. Ratcheting itself apart thru dust incursion. So
even a tiny amount will amplify over time.
Is your floor "extremely stiff"? I have no idea what constitutes
"extremely stiff" here.
Maybe the flooring manufacturer does.
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.
The floorboards run perpendicular to the joists because the subfloor
sags between them, and that allows the finish floorboards to roll,
giving you a wavy floor. THe stiffness of the joists is totally irrelivent,
because it's the ability of the 3/4" subfloor to span the 16" between
joists that's at issue. If you're not willing to rotate either the joists or
finish floor the other way, then you should do one or more of:
-use the thickest plywood you can find for the subfloor,
-change the joist spacing to 12" instead of 16", or
-put down a layer of Homasote between the subfloor and the
Or you could look into obviating your "more expensive framing direction"
by using more than one beam to support the joists, thus reducing the
Budy wrote:>Geez when you think about the look of a hardwood floor, how would
If the subfloor isn't up to snuff, the sagging between joists will allow the
floor to "roll", cracking the finish, allowing dirt to enter and wedge away the
boards from each other. The OP's subfloor is 3/4 over 12 inch O/C engineered
joists. I think he'll be fine. Tom
Work at your leisure!
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