floor joists - span length - max load

[kyra08]

Hi everyone,

I am remodeling a recently bought home. One of the upstairs rooms is a game room and I plan on putting a pool table (1000 lbs) in it.

The original floor joists were 2x6 16" OC - I glued and nailed another joist on to existing joist - so now it is 4x6 16" OC. If I would add another joist in between, that would make the joist system 2x6 8" OC. The joist span is 13'.

I wonder which one would be better, that is, 4x6 16" OC vs. 2x6 8" OC.
How can I find out since there are no calculators I can find online that will allow me to get the appropriate spans as a function of sistered 4x6 joists or at a spacing of 8" OC?

The thing is the former owner added a second story, but did not reinforce the 2x6 ceiling (floor for the 2nd floor) joists. He simply laid 2x4's perpendicular to the "ceiling" joists 16" OC and used a single layer of tounge and grooved 3/4" floor boards. Upon inspection there are many places where the crossing 2x4 do not even tough the underlying joists.

The rest of information: Southern Pine grade #2; dead and live load of 10 and 40, respectively; L/360 deflection.

Maybe you could help me with an exact answer or tell me where should I look to calculate myself.
Thanks in advance!
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[ausdesign]

AS1684.1 [Design Criteria] lists calculations for loads & AS1170.1 refers to 'Dead & Live Loads & Load combinations'.

[kyra08]

Thanks - but would the codes match the US codes?

[DvdHntr]

AS1684.1 [Design Criteria] lists calculations for loads & AS1170.1 refers to 'Dead & Live Loads & Load combinations'.

Have to pull you up on that one. AS1170 actually uses "Permanent and Imposed Actions" now

In answer to the question. You are better off to consult and engineer in the US, as the codes are obviously not the same. You could do the checks against the Australian code and feel confident but if you are ever queried then it may not meet US codes, then again it may.

[thebuildingsurv]

DvdHntr I think he was referring to the title of AS 1170

[DvdHntr]

Yeah, it is called Permanent, Imposed and Other Actions.

[thebuildingsurv]

yeh thats AS/NZ 1170.1, AS 1170.1 is the one peter was refering to both are referenced in the BCA

[Dirty Doogie]

As a general rule additional intermediatte timber joists will hold and transfer point and live loads better (without bounce) than built up joists at wider spacings. As you are in the USA I cannot advise what spacings to use becuase I dont know the timber grades / species in use there.

One thing to consider however is the wall structure holding the joists - ideally there should be a stud under or close to the point where the joist rests on the wall frame. If it is the case that the new intermediatte joists DON'T have any support under them - then doubling up (even tripling) the existing joists is the only way to procede.

To gain any benefit from doubling up joists the end of the joist must transfer load. If you simply fix another piece of timber to the side of the joist without resting the ends on a support, all you are doing is making the joist heavier but no more structurally stronger.

If your existing joists are pine or softwood then the timbers will definitely need reinforcing to carry the weight of the pool table.

[DvdHntr]

We can tell him about the methods in Australia but it is better if he gets advice on this from an expert on the US codes.

What Dirty Doogie said is correct though. The best solution is to either laminate extra timbers onto the existing joists or put in more joists, taking care that they are adequately supported by the walls below (studs under joists).

I think you will find that AS/NZS 1170.1 is the current version as AS1170.1 was released 18 years ago. I know the BCA has both referrenced but it is better practice to use the most up to date standard.

[addo]

...I wonder which one would be better, that is, 4x6 16" OC vs. 2x6 8" OC.
How can I find out since there are no calculators I can find online that will allow me to get the appropriate spans as a function of sistered 4x6 joists or at a spacing of 8" OC?

It shouldn't make any difference as I see it - if you consider the fourth moment of area determining the bending, then bh³/12 is simply double with the sistered joists - yet the FLW is twice as the joist centre doubles - so it cancels out... Whichever choice is easier!

The thing is the former owner added a second story, but did not reinforce the 2x6 ceiling (floor for the 2nd floor) joists. He simply laid 2x4's perpendicular to the "ceiling" joists 16" OC and used a single layer of tounge and grooved 3/4" floor boards. Upon inspection there are many places where the crossing 2x4 do not even touch the underlying joists.

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Are the 2×4s laid on edge or on the flat? If they're on edge, getting everything rigidly hooked up will add a fair degree of stiffness, too. Improvise with 2×1 cleats running from one up to the other and gunned or screwed in.

Now - the pool table - I'm assuming four legs, so 1000lbs=250#/leg. That's not a whole lot but it could punch through a softer floor medium when a heavy guy leans on the table for a shot! what about doubling up on the flooring with either a ¾" OSB or ply underlay, or strategic stiffening around where the feet will go? I mean, trim it out with a bunch of 2×4 at close spacings. Even add a ledger below to sit them all on; that might make for improved accuracy on the top heights.

A final hint: Photograph the floor framing before you close it all up. Next time you need to tap into the wiring, fix a leak etc - you'll know better where it is.

Cheers, Adam.


P.S. For people who've commented on US standards vs Aussie ones - there is not a great deal of consistency, and state regulations are really the determinant. I have shared our waterproofing one with a few contractors that reckon it's miles ahead of local regs. OTOH, they have some good (in theory) rules for how you build against tornados.