# Hardwood floor direction

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 "never" rule?
Len
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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.
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Chris Lewis wrote:

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 the 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 finish floor.
Or you could look into obviating your "more expensive framing direction" by using more than one beam to support the joists, thus reducing the span.
--Goedjn
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Geez when you think about the look of a hardwood floor, how would the direction is runs in effect it in any way?
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Budy wrote:>Geez when you think about the look of a hardwood floor, how would the

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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