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floor joist spacing

floor joist spacing

floor joist spacing

hello all,
I'm preparing plans for a 2 story + basement house and had a question on the floor joists for the first floor. I have specified 2x12 @ 24" OC SPF #2. the loading is 50psf LL + 10 psf DL. the joists work for l/360 deflection and are close on allowable stress. the house width is 28' with a center beam so the design span is slightly < 14'. the house is in NY. My question is will 24" spacing be ok for hardwood flooring, a local contractor recommended 16" spacing to make sure there is no problems with whatever flooring system the owner decides on using. thanks....
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RE: floor joist spacing

I did a little calc, I cant get 2x12 at 24 with SPF.  Just go 16".  I always use 16"  I think the spacing doesnt matter.  They space it at 8, 12, 16, 19.2, 24, 32 because they can lay down the OSB.  So they can the edge on a joist instead stopping in the middle.  I think you should stick with 2x12 @16.  I always use LL/480 and TL/280 for floor.

RE: floor joist spacing

I agree with COEngineer.  I always use 16" O.C. for residential (mostly because that is industry standard in residential).  Also, I use L/480 for LL deflection.  This generally gives you enough stiffness in your floor system to limit vibration and to also limit cracks in brittle floor finishes such as tile.  Also, SPF material larger than 2x6 here is not readily available.  We use SYP #1 for anything larger than 2x6.    

RE: floor joist spacing

Oh my.. i just read my message.. I didnt do complete sentences.. I wonder what happened.  What I was trying to say was, hardwood goes on the plywood.  Easier to lay the plywood down on 8,12,16,19.2,24, or 32.  So theortically you can space your joists @14" but then they will have to cut a lot of the plywood because you want the edge of the plywood on the joist for nailing.

RE: floor joist spacing

The Tile Council of Americal only recognizes 16 inch spacing for joists supporting tile or stone as viable.
I would stick with 16 inch spacing as stated by others.
Also, I would expect for 14 ft spans, 2x10's wouldat 16 would satisfy most performance requirements (especially if #1 S pine of D fir. #2 might also work. L/480 live load requirement is a common standard for good performance. Ther eis much written about this in some of the engineered wood joist producer's sites.

RE: floor joist spacing

thanks for the advice, I will go w/ 16" spacing

RE: floor joist spacing

does anyone specify lateral bracing (diaphragms) for the joists? i was considering 2x10 at 1/3 points on the joists.

RE: floor joist spacing

We use bracing per the NDS.

RE: floor joist spacing

If you are supporting a hardwood floor it is possible to go to a 24" joist spacing.  Size your joists for the larger tributary width, but also design the structural subfloor to meet at least the minimum APA guidelines, see their "APA Performance rated subfloors under hardwood flooring", its free at www.apa.org.

If you are supporting a tile or stone finish, agree with above posts that 16" is best, particularly if you don't know exactly what the finish is going to be yet.  

RE: floor joist spacing

check your link, it goes to the american physcological association.

RE: floor joist spacing

Sorry about that, correct link to main site is www.apawood.org,
then go to publications, then technical papers.  Cheers

RE: floor joist spacing

I do not think there would be any problems with either 16" or 24" spacing at all for that span, occupancy and module. However, If a heavier floor finished is desired I would just specify (2) 3/4" plywood subflooring.
Another consideration beyond what is structural would be that extra room for ductwork if joists are spaced at 24".

Hope it helps.


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