Hard wood flooring 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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Len wrote:>I am designing a new house. We will be using 12" engineered joists

Len When running the ply perpendicular to the joists, why not? Tom Work at your leisure!
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I am confused. I have seen hardwood flooring running 2 different directions in a house depending on where the joist ran in a house. Is there a reson why you want the flooring to run a certain direction?
Plywood does all kinds of crazy bowing and dipping. When you nail into those valleys it may not be pretty. The flooring that runs perpendicular to the joists is usually spanning a joist or 2 or 3. Of course that depends on the wood you install. My house has engineered joists on 19.2 inch centers. How they came up with that number in Atalnta Ga. I'll never know.

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I think the 19.2 inch centres is the whole number to allow increments of exactly 8 ft for the subfloor. 5 x 19.2 = 96 in = 8 ft but still have a wider spacing than 16in. I expect 24in spacing would result in the subfloor needing to be increased in thickness too much.
Dave Paine
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Well that makes too much sense. Almost 7 years and I never thought enough to figure that out.
Thanks.

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The builder is trying to save a joist every 8 ft. Cheap builder. Panel stiffness is the cube (power of 3) of the span. (19.2^3)/(18^3)= 1.21
21 % more deflection. Good for creaky floors.
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The floors do not creak. I have been living in the house for nearly seven years and the floors are silent. Just like the brand name on the 14" joists. The builder did not give a rats butt about cost. I wrote all the checks for materials and labor. The floor joist size and spacing was based on some computer program the joist vendor made. I guess next time you come over for a visit you can stomp aroung the house and tell me which areas have joists 19.2 on center and which has joists 16" on center. ;-)

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On Wed, 22 Sep 2004 03:11:11 GMT, Jim Behning

Are those engineered joists? It sounds like they are.
Engineered and metal products can carry different usage specs as 2x joists.
Barry
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Well yes. I would have screamed all kinds of stuff if they tried to install 2x lumber in such an odd spacing.

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With 'standard' spacig being 16", not 18", it's even worse 19.2^3 / 16^3 = 1.728
Ouch!

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