I am currently finishing my basement and looking to install a bathtub. I have already decided that I will be using a sub-floor in the basement.

My question is: Should I place the bathtub directly on the concrete or place a subfloor down first then install the bathtub?


In most cases if you place the bath tub directly onto an existing concrete floor you will then have to remove the concrete in the area around the bathtub drain to permit room for the drain basket, drain pipe and P-trap. Sometimes you get lucky and the bathtub drain lines up perfectly with a drain line that comes up just through the concrete floor .. and .. the necessary P-trap is already in place under the concrete surface.

If this is not the situation that you have then it may be necessary to have the tub on the elevated floor. This can leave just enough room to route a drain pipe from the tub drain over to where there is access to the necessary further parts of the drain line.

  • We've already plumbed the p-trap and drain lines from an existing rough-in that was underground. The alignment looks good I was just wondering from a "good practice" stand point. Would you say that a direct to concrete tub installation makes the most sense? – Cameron Feb 26 '19 at 2:39
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    I would put the tub on the concrete only if the "sub floor" that you talk about is just floor covering material thick. If your floor is raised up some amount (couple inches for instance) it will feel strange stepping in and out of the tub because you would be stepping down into it if it were on the concrete. I know in the olden days when claw foot bathtubs were in use you stepped up into them and even that has always felt odd to me. In addition there may be some unanticipated difficulties sealing a raised floor against a sunken tub. And it would certainly be more difficult (continued) – Michael Karas Feb 26 '19 at 2:51
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    (continued from above) to remove a sunken tub in the case you had to do some repair or to replace it. – Michael Karas Feb 26 '19 at 2:51
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    The sub-floor will raise the floor an additional 7/8". It consists of DMX and 3/4" OSB. So by what you are saying and what my instinct was is to just put the tub on the sub-floor surface. Thank you for your reply! – Cameron Feb 26 '19 at 2:54
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    I would run your sub floor under the tub. If you ever change the tub in the future the new tub may have a slightly different footprint and not fit into the old space causing additional work to remedy the difference. – Alaska Man Dec 25 '19 at 0:21

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