[notahacker]

I think the main challenge with modular bathrooms integrated into an otherwise traditional build is that you're plonking a finished unit into a rough-and ready site that has no pipes or wiring to connect to yet and people running round laying bricks and lifting in beams... which feels a little premature. You're not going to fit one through the doors of your average existing building either, and the economics of hiring a large crane just for the upstairs bathroom rather than the entire build probably make less sense

It's a bit different when the modules are part of a hotel/apartment block that's entirely built using a modular system. That's common enough in city centre hotels and motels where they're a single full-sized room and nobody can tell the difference.

[bluGill]

Hiring a crane to put the roof trusses on isn't unheard of. It costs more than a large forklift (which you have onsite to move piles of lumber around anyway), so it isn't normal, but where the terrine doesn't allow the forklift to get the trusses in place crews will hire a crane. I've also seen crews (generally of old people - almost of retirement age with the typical failing body that come from years of hard labor) hire a crane to life their walls up, such crews are still competitive with other crews so in the scheme a crane cannot the that expensive.

If it became common I'm sure crews will switch to using a crane for the roof, just because the crane will be there to lift the bathroom in place anyway. However someone needs to start making the factory bathroom first and convince builders to use it.

[jaclaz]

They (prefabricated bathrooms) are sometimes used, but they do bring a number of issues (I am talking of "real" prefabricated bathrooms, concrete, not the plastic/fiberglass ones that also exist), a few of them:

1) they are heavy, the actual structural design needs to take this weight into account

2) since they have an "own" floor you either have a step to enter them or you need to have a somewhat thicker underfloor on the rest of the house

3) since they have an "own" ceiling, the internal height will be smaller than the rest of the rooms (here in Italy this is not an issue from the techincal norms as rooms are minimum 2.70 m and bathrooms and corridors can be only 2.40)

4) since there is the need of connecting the internal utilities, electricity is the lesser problem, but typically you have two or three (cold and hot + in some cases circulating) running water pipes, two (at least) drain pipes, two or more venting pipes and the radiator (or under floor) heating, you need some additional space on the outside or some (not really pleasing to the eye) boxes on one wall or in the floor (or both)

In practice the only kind of building where they make sense are new multi-storey, multi-apartment buildings and hotels, hospitals, prisons, etc., and even then usually they are not usually much cheaper, they are only much faster and easier to put up, and definitely have an advantage for "luxury" bathrooms where local workmanship capable of a high quality work are not available or cost too much.

An example, this is an Italian builder of such "pods" with experience in international projects:

https://www.eurocomponents.eu/en/portfolio

https://www.eurocomponents.eu/en/modular-bathrooms-for-inter...

[bluGill]

If you design for it, floor trusses with a lower section that the pod can fit into can be had, solving the step objection.

I agree overall with your point though.

[jaclaz]

Yep, it is possible, but it is not something you would normally do.

Usually these pods are lifted by a crane and "inserted" in the building (talking of reinforced concrete buildings) after the structure has been built (before building the outer walls).

Once they are on the floor they are moved manually on carts/wheels attached to the pod structure, so it is much easier if everything is at the same level, the lowered level of the deck (only where the pod goes) would add another complication in the moving/placing.

With the advent of underfloor heating the thickness of the screed is increased anyway (compared to the old buildings) so the "step" is not anymore a problem as it was years ago.