I’m installing a Kohler Purist bathtub on the second floor of a Cape Cod. The floor joists consist of 2 x 8’s, sixteen on center, with a span of roughly fourteen feet. One end of the joist sits on a masonry front wall, while the other side sits on a doubled up 2 x 8 header installed when the bearing wall separatng the former bedroom was removed to make an eat in kitchen. My question is, by adding a tub that can hold approximately 115 gallons of water (not that I would probably fill it that full), how much extra framing (ie. sistered on LVL’s, etc.) do you recommend I add—-OR, do I need to increase the side of the header carrying the weight on the one side, OR both? Or nothing at all, but I doubt anyone will come back with my hoped for answer….
BTW, Kohler’s installation sheet specs a floor that can hold a miminum 1400 lbs.
Any help appreciated!
Replies
Yep, those floor joists are not quite up to the task.
There will be some division about how much to beef it up, since some will claim the floor for some distance around the tub will pick up part of the load and help support it. It will, but only after the joists imediately under it have sagged considerably.
How much room do you have for joists--just the 7-1/2" or is there room for deeper joists due to a dropped ceiling or whatnot below?
How close the tub is to the wall and the direction of the joists under the tub will also have an impact on the support neccessary.
The header may or may not be ok, depending on how it's built and how much of the load is on it.
LVLs are relatively cheap for what they can do, so we use them quite often in these type of situations. The existing joists can be expected to continue carrying the floor (although 14' is most likely too long a stretch for 2x8s), so just ask the lumber yard to size the load and the number of 7-1/2" lvls needed to hold up a point load of 1400 lbs. however far it is from the ends of the span and add them between the existing joists.
You'll also be fighting the sagging floor so the ideal fix would be bringing the entire floor framing up to speed with some additional 2x8s either spaced between the existing joists or sistered directly next to them with pl10 to prevent squeeks.
At least that's how we would handle the whole situation for a client.
Cheers
The tub is six feet by four feet roughly, and it sits in the middle of the floor span, perpendicular to the floor joists. The kitchen underneath the tub is gutted, so tearing down the ceiling and sistering on new LVL's is not TOO big a deal. Do I have to do the entire floor or just under the tub? If I triple the 2 x 8 header, will that suffice? ( The header is hidden in a soffit, but I've already run drain lines in those pockets. ) If it were acceptable to skip one joist bay (where the plumbing is) or to sister on the right side of one joist and then the left side of another would be great,
Thanks Trout, and everyone else for their advice!
This thing is a monster tub!a. Using LVLs, sister each of the joists below the tub.b. Install solid bridging between the joists, minimun 2 bays beyond the perimeter of the tub.c. Beef-up the beam. Someone needs to do the math. Note: beams should be balanced along their length axis - think "a balanced sandwich."d. Once you resize the beam you will need to resize the posts at each end for bearing the new load and beam size.Frankie
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Well said Frankie.
It also matters how the tub sits relative to the joists. Parallel to the joists in the middle of their span would be the worst situation, perpendicular to them up against one end would be the best. How many of the joists are actually under the tub?
I did this exercise with 2x10 joists and a diagonal wall, so the spans ranged from 13' to 16', and ended up sistering four of them. I also had to put a new footing in the crawl space under the inboard end.
-- J.S.
I agree with trout. If you have a finished ceiling below that you don't want to mess with, and not enough room between it and the floor the tub is on, could you put new, deeper joists in and let them be above the existing floor and have a slight step up into the tub--or even put the tub on a platform? A tub full of water and one or two bathers is a lot of weight.
If your floor is to code (40pounds/sqft), I expect you will have no problems as is.
You could pay an engineer to do the numbers.
What Frankie said. And plan for the plumbing to work with the new framing. Once you get the framing all set, you don't want the plumber to bust out his hole hawg and show you what he can do! Or worse, put in some nice 4 inch notches to run the drain.
Aaron