Hi, All -
I've purchased a cast iron clawfoot to put into my bathroom, but I'm a little worried about the flooring.

Right now the joists are 2"x6", spaced 16", with a run of 15' Right now, I've planned to put the tub roughly in the middle of the joists, but since the room is gutted, I have to option of placing it closer to the wall.

The subfloor itself is 3/4" plywood, with no finished floor on top - I just tore out the carpeting, so I have the option of starting fresh in this room.

Is it recommended to install a few extra joists for support, or perhaps a support beam in the basement, or both? And is the plywood sufficient support for this tub, or should I provide a better base?

Thank you for your help!

that floor joisting sounds way, way light. you sure those aren't 2x8? 2x6 wouldn't hold up a baby in a bassinet.

I am not a professional engineer. but I have been left with the impression that the minimum code span over 12 feet is 2x10. that should be sufficient for a one-person classic clawfoot and its typical 40 gallons of water at 16 pounds per gallon. I had to chase the numbers a bit when I redid our bathroom to include a whirlpool single tub, and it worked out.

I heartily recommend, since you have the opportunity to open things up, calling city hall and asking the building inspectors what you need. I bet they will say you have to sister the joists, and perhaps double-sister them.

This message has been edited. Last edited by: swschrad,

2x6 is too light for a 15' span. So would be 2x8. 2x10 16" OC is good for around 15' of normal load, but not for a large tub.

Water is 8.65 pounds per gallon, a big tub will easily hold 100 gallons. The last cast iron clawfoot I installed was right around 500 lbs. Toss in a person and you are at 3/4 ton.

Beef up the joists, add support from underneath, move the tub closer to the support walls - preferably all of the above.

I checked the measurements again, just to be sure on everything. The joists are (you were right) 2"x8", but the run is 15' on those. All considered, I'm surprised the floor isn't more spongy, even when I jump on it.

But then again, the joists aren't new - I'm guessing turn of the century or older, so they're a lot more sturdy. The house is an old workshop with no existing plumbing, and I'm working on making it a livable space.

The clawfoot tub is one of the lighter ones (for an antique) and weighs roughly 250lbs, and it has a roughly 70 gallon capacity.

Sounds like I need to:

• sister the joists
  
• provide some sort of additional pillar of strength below the tub
  
• place the tub against the wall near the edge of the joists
  

Based on what I'm hearing, it wouldn't be a bad idea to run a support beam under the center of the joists to provide extra support for the entire floor.

Any suggestions on the subfloor? Is 3/4" plywood enough to support the weight of a clawfoot on those 4 claws?

The 3/4" subfloor with finished flooring on top of it will support the tub OK. You may see some sagging only if the feet are resting o a point that is in the middle of the 14-1/2" span between floor joists. If you can plan the tub location in advance, you could always add some solid blocking in the tub foot areas to avoid this.

If the basement area underneath is unfinished then the easiest and cheapest way to really support the tub would be to add a few columns directly under the tub area. Even though 2x8's are too light for a 15' span, as you say the floor does not bounce now and they have been there for a long time - if you add some support directly underneath the tub then you will not have to do anything else to the rest of the floor framing.

Are you jumping on it by yourself or is someone jumping while you are standing there.?
Take and cut strips of 1" plywood about 1/8-1/4" narrower then the 2 x 8's, glue and nail the strips on both sides of the 2 x 8's making sure to stagger the joints by at least 2' - 4'. Install your joist ties, 2 per joist spaced equally.

I've had someone else come in to jump on the floor while I stand still, and vice versa.

After a lot of consideration, we've decided to run a series of support beams under the entire house, so that the floor is split into sections with each run no longer than 8 feet. We have a lot of heavy antique furniture, and there's no sense taking risks just to save a few bucks and time.

Additionally, we're going to give extra attention to the joists where the tub will sit, and sister those joists.

And, finally, we've decided to go with a 3/4" plywood platform for the tub, so it can have extra support in the foot area, and we won't run the risk of it damaging the finished flooring that will be put in rest of the house.

Thanks for all your help - it's been much appreciated!