Redoing a second floor bathroom: question on the weight of Tub?


chrisbouch2002 asks:

I’m going to be redoing my upstairs bathroom and moving the bathtub so it goes parallel to the joints. I’m planning on putting an additional subfloor down however should I worry about the weight of the tub? If so, any ideas of what to do?

Best answer:

Answer by buddy w
most tubs are now made of poly resin and fiberglass lightweight and easy to move just make sure you have no water leaks when finished

5 thoughts on “Redoing a second floor bathroom: question on the weight of Tub?

  1. Take the height & spacing of the joists, for instance, 2″ x 10″ on 16″ centers, then look it up in a span table. You might find a span table here:

    A Kohler Mendota cast iron tub weights in at 370 lbs + 45 gallons of water @ 8.35 lbs/gallon + a person (standing) gets a total weight of 945 lbs over 32″ x 60″ or 13.34 sq ft results in a load of 70.84 lbs /sq ft. (this may not be evenly distributed, but I don’t know how to account for that).

    Having said that (and hoping that the math is correct) I have installed & serviced many cast iron tubs and never come across any sort of support issue.

  2. With all due respect to you and others, and BTW I’m leaning toward one concept JAKE suggests. You state JOINTS, not JOISTS. Define JOINTS.

    First of all the Joists/beams/rafters; whatever you want to call them; that support the second story; especially where the tub is located; should already be situated over a LOAD bearing support structure below. To move the tub off that support is a bad idea.

    With no offense meant to one answer stating materials other than IRON/Enamled tubs; That might actually be better in the sense of a tub on any level but a Slab.

    It would help you to know the load bearing capability of the per. sq. ft. of that second level floor.

    As others suggest. Water weighs 8.5 lbs. per gallon. A usual tub might hold 50 gallons for a deep, nice bath. Adding another/additional sub floor is confusing, unless the purpose is for more than just supporting a tub. All you’re doing is adding weight to the support structure holding up that area of the second level.

    So, considering the weight of any tub; plus 425 lbs. of water; plus or minus; and the weight of the body in the tub; Say for arguments sake a total weight of 685 lbs. plus or minus; I’d be curious to know what parallel means to you; and I’d not strictly want to be sitting below; relaxing; watching my new LCD TV while anyone was bathing.

    Just my 2 cents.

    Steven Wolf

  3. By moving the tub parallel to the floor joists could possibly be a problem. First there is a possibility that you may have to remove a joist to accommodate the tub drain which would weaken the floor and like another answer suggested the weight of a empty tub is probably not a concern, but with the tub filled with water you would have to be concerned. If I were you, I would consult with a structural engineer and have him or(her) advise me on how it should be done. It is better to be safe rather than sorry.

  4. The best time to address this is NOW. It may be able to carry the load of the tub and the water(8lbs per gallon), but wouldn’t it be better to sister some lumber to the existing joists now? I would, even if the tub was going in the same location. Overkill?? Better than a tub falling through the floor.

  5. would not worry about the weight of the tub, i would worry when its full, of water, 1 gal weighs aprox 8 to 9 pounds,
    if it held it before it should still hold it,

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