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I am asking myself if there is any way possible to lower the bathroom floor level without causing damage to the floor.

So I am researching if it is any way possible to install a Japanese unit bath system, which basically is a shower in a (deep) tub but completely isolates itself from another room, in a typical American housing.

Here's an example: unit bath system in Japan

This type of bath system is commonly used in a regular household in Japan, and major companies like Toto and Panasonic sell the bathroom system/room as a whole as a set, which their contractor can build it together for customers (hence the name "unit" bath).

One key feature of it is the depth of its tub. In general, their tub is much deeper than one in the US as it is designed for soaking and relaxing. Thus, their unit bath system is generally designed to lower the bathtub floor height to accommodate with the bathroom floor level.

HSV-1616 unit bath system HTV-1616UT unit bath system

As you can see in the above illustrations, look how its ground level is lower than the bathroom floor by 197mm and 450mm respectively, and this brings back to the question above.

Obviously, one solution is to make it for a basement bathroom so I can dig up a hole and don't have a joist to worry about, but say if I don't have one. Another option would be simply to place the system directly on the ground floor and live with 7 3/4" steps, but I was hoping for a better solution. Not to mention, there would be a tub that holds 110gal + person's weight. Trimming a joist seems just too much of a risk to me... Any thought anyone?

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  • Welcome to Stack Exchange. You should take our tour so you know our site works with upvotes for helpful info and checks for accepted answers. – HoneyDo Feb 25 at 4:31
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    In your diagrams it looks to me like the entire bathroom floor is raised, on screw jacks like a typical commercial raised floor. Can you do that? You would have a step into the room and a lower ceiling. – jay613 Feb 25 at 11:30
  • You are right, in Japan, double-layered, raised floor is commonly used throughout the house even at a regular residential (so that they have a space to take off shoes at the entrance called "genkan"). That is why they have no problem having empty space between the flooring and the subfloor. Raising an entire bathroom by 8" seems an awfully complicated job, but yes, that also seems to be a valid option to take. – Shun Feb 25 at 13:23
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    Another option for you ... there are beautiful deep tubs designed for use in the US. Maybe not quite as deep as this but almost. Instead of using this bathroom-in-a-box you could get a tub designed for US construction and plumbing, and put some thought and design into giving the rest of the bathroom whatever kind of Japanese aesthetic feel you are going for. You can probably do a lot better than Panasonic at creating a beautiful space with Japanese styling around a deep tub and it will cost less and give you fewer engineering problems. – jay613 Feb 25 at 13:51
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    PS -- because I am not Japanese, the only exposure I have to one-piece bathroom systems is on airplanes and $49 business park hotel rooms. You might want to consider that to most Americans, such a bathroom will not convey the same ambience as it does to someone who grew up with them in their homes. IE, you might be devaluing your house by installing this. – jay613 Feb 25 at 13:57
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You need to lower the top of the joist by like 4 inches. trimming them down is not going to work.

You could move the joists down and attach them to the sides of the beams using joist hangers, that's going to lower the ceiling downstairs.

You could talk to an engineer and get some steel joists designed: you can probably use 4x4 RHS as joists (which seems to be what's in the drawing), but you need to know which wall thickness of RHS, and the engineer will be able to tell you which.

If the joists partly go under another room that's going to complicate things.

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    RHS = what exactly? – FreeMan Feb 25 at 14:28
  • Rectangular hollow steel – Jasen Feb 26 at 3:32
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Short answer is no way. You aren't trimming you are taking out the joists there. It wouldn't even work with a 20 pound tub and a 100 pound person. Also if it is a no the step option shouldn't be an option. I have seen this on many a house and what the hell do you do at the top of the step, dive in the tub? I am rather tall and have dealt with it, can't imagine someone shorter or older. Not to mention making this look luxurious is almost impossible with the step method. I have never seen it done where I was like "wow that looks nice".

Long answer yes you can do anything with enough money. If your joists are parallel to the tub it is a bit cheaper (probably) and you can simply have an adequate header installed to carry the joist load. Now I have no idea what is below this part of your basement but you may need a pole or a wall or whatever. With enough money thrown at it an architect can design a way to carry the load for sure. This could range in as little as 2k up to 10-12k (plus maybe an out of place wall/pole).

If I had already bought this and can't return it, it would unfortunately go in my basement. I can't see paying for something like that, having it installed quirky, and then effecting other parts of my house.

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Your concerns about reducing the depth of floor joists to accomodate an ofuro bath are well founded. The dimensions you are talking about (197mm) or about 8 inches would negate any joist at all without rebuilding the flooring and encroaching on the lower level. The weight of the tub plus the water and an adult would need the full support of a properly constructed floor.
If you don't want to move the tub to the basement you could build a surround that would permit a person to step up and into the tub. We had considered a steeping tub in our home and planned out just such a design - maybe a future project for us.

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  • Thank you for clearing that out! Now that I think of it, perhaps raising the rest of the bathroom floor (obviously not whole 8" but maybe an inch) may help a bit in combination with adding a step. Putting the whole system in the basement would be the last resort as the best "ofuro" experience does not complete without a window! – Shun Feb 25 at 5:55

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