We were in the same situation when we built our house almost 25 years ago. A split-level with a cast-in-place foundation slab and masonry walls on the lower level, along with underfloor heating on both levels. Our desired stairwell couldn't be achieved in a good way with prefab flooring or wood. So the alternative was to use a cast concrete floor slab. With that, we could design our stairwell as we wanted. The only downside I've noticed is that the cast floor slab is a bit slow when it comes to underfloor heating, but otherwise, it has mostly been an advantage. Any potential waterbeds, pianos, or large aquariums can be placed wherever you want on the upper level without any problem. Structure-borne noise is also reduced compared to, for example, a wooden joist floor. It took some time to make the formwork, but it was worth it.
I suggest that you try to choose a constructor near where you plan to build so that the constructor can come and check the construction site when needed. Since the forum doesn't know where you live, it's hard to suggest someone.P PetKim said:
You will have to supplement with at least some pillar and hidden beam in the floor if you don't want a load-bearing wall near the staircase opening. Otherwise, as @roli wrote, it's probably difficult to solve in any other way than with a cast floor.
What can be done is to place the heating loops in 30mm grooved EPS on top of the floor, hopefully avoiding the problem of sluggish underfloor heating.
Yes, it's a curved staircase that creates an opening of about 2.4x2.4 m in the floor slab... I don't understand how I could think like that, but now I've gotten stuck on the idea.. 
Moreover, there is no wall by the opening on the lower level (see sketch) but walls near the dashed lines. I could imagine a steel post at the filled small square where the staircase comes down.
Peter
Moreover, there is no wall by the opening on the lower level (see sketch) but walls near the dashed lines. I could imagine a steel post at the filled small square where the staircase comes down.
Peter
W Wiklundo said:
Thanks! Yes, there are several advantages, but the concrete scares me. I have built several wooden joists myself and know what it involves - and can then solve things at a slower pace. With water, sewage, ventilation, electricity, and 100 other pipes I will want to secure if it's to be cast, I get a bit panicked... Additionally, I have understood that the underfloor heating will be problematic when it automatically also heats the ceiling on the lower floor... (will have simple mechanical exhaust).R roli said:
Have you cast in water heating loops directly into the concrete joist? Does it affect ventilation/climate?
Peter
The house will be built in the middle of Skåne.
I've worked with EPS, but the idea is that parts of the upper floor should have tile flooring, so it doesn't work well together. And if the loops are embedded, there will likely be problems with heat in the ceiling downstairs, from what I've heard - in addition to the sluggishness.
I can have a post where the stairs come down - but unfortunately not where the stairs start - and it is curved, so the hole in the joists will be about 2.4x2.4.
Peter
I've worked with EPS, but the idea is that parts of the upper floor should have tile flooring, so it doesn't work well together. And if the loops are embedded, there will likely be problems with heat in the ceiling downstairs, from what I've heard - in addition to the sluggishness.
I can have a post where the stairs come down - but unfortunately not where the stairs start - and it is curved, so the hole in the joists will be about 2.4x2.4.
Peter
We have the loops embedded in the floor slab but insulated the underside with 50 mm cellular plastic, so we don't have any heating problems on the ground floor. Sure, there are a few things to consider when it comes to getting all the pipes in place, but it's not impossible. We have electrical conduits, underfloor heating loops, pipes for cold/hot tap water, and c-vacuum pipes embedded, along with passages for mechanical ventilation. If you go through everything a few times to ensure you don't miss anything, it works. In hindsight, we probably should have placed the underfloor heating on top of the concrete floor slab to make the heat less sluggish, but that's probably the only thing I would change after almost 25 years in the house. Much of the wiring in the ground floor ceiling is also in a raised ceiling, so it can be altered if needed.
Here is a proposed solution when underfloor heating is above concrete floors: https://www.lksystems.se/sv/produkt...system/pa-barande-golv/lk-sparskiva-eps-3050/
Works with all types of flooring, including tiles.
Works with all types of flooring, including tiles.
Thanks! I see EPS works with tiles now - but it seems you have to self-level with EPS-cement over it. Nevertheless, it's a good solution - if it ends up being a concrete slab. I'm still looking for alternatives for wood/steel - we'll see if it's possible. Thanks for the help so far! Peterpdov said: