Dose anyone know how I can find out what the load a 2x8 can carry? I have a whirlpool tub going in over some 2x8's on a 12 foot span. The tub filled with water weighs approx. 750 lbs. or 54 lbs per sq ft. Would like to know if I'm ok or in trouble.

 

OK, you have some number of 2x8's on a 12' span. I would say that you have a problem.

Your calculation shows nearly 14 sq. ft. of footprint for that whirlpool tub. Let's say it's 5'x3' dimensionally. That load is too concentrated for a 12' span supported only at the ends. The 2x8 material will eventually deflect, particularly when a 200# person gets into the tub. Now you are nearly at 1/2 ton center loading a 12' span. Looks risky to me.

 

Sorry, and thank you for your reply. the 2x8's are running the long way in a 5x8 bathroom The tub is a 32"x60" whirlpool. There are 5-2x8's. Hopefully this helps my situation?

 

OK, it's a 5x8 bathroom. Where's that 12' span located? A bit more information please. The floor of the bathroom is
a) concrete
b) wood
c) located on the second floor of a house

The tub containing only water is 54 #/square foot. With a 200# adult in it, that's 67 #/square foot.
If you perform a Google search for 'span tables' you will see that the greatest span in this load range is about 8-10' spaced 12" O.C.

This load concentration would require some type of pier or pad beneath the floor with posts/beams supporting the floor from below.

 

Not enough info!

As stated, 12' is too long a span for 2x8's. However, if the 2x8's are supported at mid-length with a girder (4x6 or 4x8) then it should be OK.

Also, the location of the tub makes a difference. Is it located near one end of the 2x8 joists. Judging by your statement that there are 5 joists supporting the tub then I would guess that the tub is adjacent to one of the support walls and parallel to it.

In order to determine what will work, a lot more info is needed than you've given so far. That's why Architects and Structural Engineers are so often recommended to look at these problems.

-Joe