span length for reinforcing 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!

[Redoverfarm]

To be honest with you that is not much of a floor joist. More than enough for a ceiling.  Hindsight is always 20/20 but If you really wanted to stiffen it up I would have used 1/2 or 5/8 OSB glued on both sides and then apply your additional 2X6. Like you would sandwich the OSB between the two.

I found this deflecto calculator on John Bridge for tile and marble but they all work the same. I am not sure you could run it as a 3X6 and see what you get.

I am sure there is someone on the board with more structural knowledge than me that can put additional light on the subject.

http://www.johnbridge.com/vbulletin/deflecto.pl

John

[glenn kangiser]

You could probably double the single 2x6 load if you doubled the 2x6's -- each will support it's own portion of the load so 2x will carry twice the load.  

What is the span you are supporting - how wide is the room?

[peter nap]

Actually Glenn...I think the sistered 2x6's will carry more than double the load but I don't have a clue how you'd calculate it.

Flex would be my biggest concern at this point and i agree that a sandwich of OSB would be the solution. Still not too late to consider it.

[MountainDon]

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.

Were you able to get the added joist slipped in on top of the support, or is it just doubled up up to the support point. Just doubled will create more stiffness, but without the extra end bearing the floor strength won't be doubled.

Most joist calculators are set up to work just with 2x material. Like this one...
http://www.awc.org/calculators/span/calc/timbercalcstyle.asp?species=Spruce-Pine-Fir&size=2x12&grade=No.+2&member=Floor+Joists&deflectionlimit=L%2F360&spacing=12&wet=No&incised=No&liveload=50&snowload=-1&deadload=10&submit=Calculate+Maximum+Horizontal+Span

The John Bridge calculator is very nice for calculations on floors where ceramic/porcelain tile or natural stone will be installed. I've found it handy in the past. It's nice that it does larger materials as well. You should have no problems running it at, say 3 inches width for fully doubled up 2x material.

I could be wrong but I believe that most additional strength would come from extra joists. The plywood or OSB may add some strength, but in constructing a built-up beam/girder the 1/2" ply/OSB is mainly there for spacing the 2x material apart to fit standard size metal brackets, like Mr. Simpson's.

[mikemgi]

thanks Kyra for helping.  This is the owner of the house. The guy that remodeled the house did not get a permit and now i'm left to try to correct his mistakes without tearing up the entire second floor.

yes the added joists are supported. 

I have not worked on the room under where I want to put the table yet.  I'll write more when I get off work, but the guy ran 2x4's 16" OC perpendicular to the ceiling joists and secured toungue and groove subfloor this this lattice.  I had a structural engineer make recommendations - He suggested dbl 2x6's and that I position two of the pool table legs over the 2x4 lattice that the 3/4 inch subfloor is secured to.  The engineer did not recommend blocking, which I plan on doing.  The span in the 1st floor bedroom below where I want to put the pooltable is 13.5 feet. 

I like the idea of OSB.  I think this will help with deflection. 

anyway - thanks

mike
the guy who did the remodel

[glenn kangiser]

Welcome to the forum, Mike.  I think you are the first new member since the switch today.  Sounds like this will work out for you.

Glenn

[kyra]

No problem, Mike. Glad you're back in town to take it from here. Wish you good luck and good work!

It was nice meeting all you guys in this forum! 

Thanks to all and all the best,
Kyra

[JRR]

If you double 2x6's that are 16" oc, don't you now have 4x6's ... but that are still 16" oc?? 

Or do I need a big cup of (well laced) coffee?? ...

[glenn kangiser]

I'm sure you must be right, JRR -- although for some reason I didn't think of it.  Just skimmed over it...but the space between must go down 1 5/8" or so.

...and I need the coffee -thanks for the reminder.

[kyra]

If you double 2x6's that are 16" oc, don't you now have 4x6's ... but that are still 16" oc?? 

Or do I need a big cup of (well laced) coffee?? ...

No - you are right - they are still at 16" oc. It was my mistake - I typed it wrong.

Sorry about that,
Kyra