Upstairs bathroom, will it continue to hold!

[AG A]

If the joist is only designed for 200kg and you load it with 300kg, you are overloading the joist. This can lead to significant deflection or, in the worst case, collapse. However, as you heard, the joist should withstand 400kg/m2, considering the free load. Therefore, you can, simply put, have a fixed load of 300kg without problems, as long as not too many people are in the bathroom at the same time.

These loads/forces are what are used nowadays when designing joists. It’s also not the case that it will only hold exactly these loads. Rather, it’s what it should at least hold. It often holds more/much more. To my knowledge, these load standards have not changed since -69, so it should be the same for you. You won't reach such a high total load.

 

[Kirre2021]

If the floor structure is only rated for 200kg and you load it with 300kg, you are overloading the structure. This could result in significant deflection or, in the worst case, a collapse. However, as you mentioned, the floor should withstand 400kg/m2 if we include the free load. Therefore, you can, in simplified terms, have a fixed load of 300kg without issues, as long as there aren't too many people in the bathroom at once.

These loads/forces are what are used nowadays when designing floor structures. It's also not the case that it will hold exactly these loads—it holds at least that much. Often, it can hold more/much more. To my knowledge, these loads haven't changed since '69, so they should be the same in your case. You won't reach that high of a total load.

Thank you for the detailed information. One last question if it's possible to answer. What is considered significant deflection concerning wooden beams, disregarding experiences like sloping floors? I'm thinking is up to 5cm in the middle far from the breaking point, or is it close to the point where the beam could break? I think this might provide a small indication of how heavily the beams are loaded, based on the number of cm of deflection.

 

[AG A]

I can't remember the numbers right now. But the allowed deflection is calculated based on the span, the height and width of the beam, as well as the material of the beam.
In your case, 5cm is approaching the breaking point, I think. 5cm would not be accepted, as it would also affect much else. It would both be visible, feel wobbly, and wall, ceiling, and floor materials would crack. I guess that about 2cm would be accepted in your case.
However, remember that 2cm is terribly far from 5cm when it comes to deflection of wood. You are very far from any breaking point if you have a deflection of 1-2cm.

 

[Niklaspe]

70x195 on cc600 are substantial pieces as intermediate joists. Then you have chipboard on top, which also binds the whole construction together and makes it rigid.

 

[Kirre2021]

70x195 on cc600 are substantial pieces for a mid-floor structure. Then you have particle board on top which also ties the entire construction together and makes it rigid.

I'm thinking that the thickness of the beam is irrelevant and that only the height carries the load?

Over the weekend, I've done further research at home and can see that the bathroom rests on a total of 7 beams. 3 of these lie over a wall on the lower floor, so it should help even though theoretically you should be able to remove it in these houses (some have done it). The span over the wall is then 3M. Then there's 1 beam at the other end resting on the entire staircase construction with a wall underneath, so the span there is 3M.

So assuming that the beams actually rest on underlying structures, only 2 beams remain with a 4.7m span.

 

[mexitegel]

The width matters, but not as much as the height. As for the chipboard, it would need to be glued and screwed into the studs in order to further increase the load-bearing capacity.