span length for floor joists

[kyra]

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 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 14" OC. If I would add another joist in between, that would make the joist system 2x6 8" OC.

I want to know which one would be better to try.

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; deflection of L/360.

Maybe you could help me with an exact answer or tell me where should I look to calculate myself.

Thanks in advance!

[suemarkp]

The one crucial piece of information missing is the span of the joists. A 2x6 joist is a rather pathetic unless you have some short span for a bedroom or a closet or bathroom (e.g. less than 10'). I have 2x12 joists on 12" centers, and drilling holes between the joists for pipes and wires is a major pain because a drill won't fit. I have to use right angle drills or adapters, and the adapters don't last all that long when drilling big holes in 40 year old lumber.

Can you rip out that crossed 2x4 and change all the joists to 2x8's? If so, that is a much better solution than 2x6's on a tighter spacing. But if this room is 16' or 18' across, I think you'll still need doubled 2x8's to get this done (or just use 4x8's).

Here's a deflection calculator that goes to 10" spacing and allows 4x joists instead of just 2x ones. http://www.johnbridge.com/vbulletin/deflecto.pl

What you really need are the equations so you can calculate it yourself.

[kyra]

But do you have any idea where could I get those equations?

The span of the joists is 13'. Lately I was thinking about OSB as a solution.

Thanks

[pushkins]

I think you will find that what you have, is and will be should you add yet another 2x6 not sufficient. OSB has little strength on a horizontal plain so I don't see how that will strengthen your floor like you hope.
My calculators show that for the most 2 x 10's are required, try the web site below, enter your specs. and lumber species.

http://www.awc.org/calculators/span/reversecalc/reversecalc.asp