Floor joists

[jel1988]

Which senario would result in a stiffer floor, (less deflection) 2*8's 16" on centre or 2*10's 24" on centre.

 

[eddie48]

My calculations say use the 2x8s. That assumes that the load is evenly distributed and that the flooring is sufficently strong to avoid deflection between the joists.

 

[oosik]

To be quite honest - unless this floor is in some type of work shed or something like that - - I would recommend 2x10 or better yet 2x12 on 16" centers. Otherwise - go with 2x8 on 16" centers.

 

[/pine]

FWIW... Row(s) of "X" bridging or solid blocking help to distribute load...this will also stiffen the system regardless...

 

[KennyG]

Your 2x10 configuration has more weight carrying capacity. A 2x10 has about 65% more strength than a 2x8 and your increased spacing will only add 50% to the load. The 2x10 floor will be stiffer over the joists. HOWEVER, the stiffness between the joists will depend on your flooring material. Whether you use 2x8 or 2x10 and the spacing should be taken from a standard joist table which is readily available on the internet. The span is critical which you did not specify.

 

[BHD]

you will not even remember the cost of the deeper joists, in time to come but if you have sag or bounce you will kick your self ever time you walk across it or deal with the sag, for the few dollars you saved,

many years ago we added on to the church, I calculate out the size of joists for the span, and it was 2x8 I think, well later the plumber ended up gut about half of them by drilling out a large portion of the joist in the middle, later we remodeled some partly because of the sagging floor, (I had no idea that they nearly gutting the joists in the plumbing but in the end we sistered up new joists along the old ones, but even where they were not hack up there was more sag than desired,

I would suggest 2x12 lumber or the I joists, I do not think you will be sorry,

on a floor use 16" on center, your floor will thank you,


(I am not seeing you distance your spanning) which can influence your choice,

 

[newbury]

Which senario would result in a stiffer floor, (less deflection) 2*8's 16" on centre or 2*10's 24" on centre.

Yes, we REALLY need to know the span for a half decent answer. Are you spanning 4 feet or 14 feet?

 

[DFB]

Yes, we REALLY need to know the span for a half decent answer. Are you spanning 4 feet or 14 feet?

What he said! :thumbsup:

 

[PILOON]

Absolutely, the span is most important.
Also a few other factors: plywood sub, strand oriented chip board etc.
All being said the wider will offer more stiffness, in fact I am sure that 2 x 10 will 'out stiffen' 2 x 8 in just about any situation as long as you don't exceed the spec for the span .

ex: on a 8' span there will be no difference but at 14' there will be a noticeable difference.
At 16' neither is within norms.

 

[Deere Dude]

Just a slight hijacking here, but in the house I just bought has 2x10 joists @ 16" and is sturdy. But I noticed all the Xs with 1x4s in between the joists were never nailed or screwed in the bottom. Should I fasten them on the bottom?

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