ᐅ Thick Floor Slab or Structurally Optimized Layout?

Architect-1 plans the reinforced concrete intermediate floor slab at 30 cm (12 inches) and has a lot of freedom in wall placement.
Architect-2 calls this "letting the forces roam" and suggests that for cost reasons, the load-bearing walls should be better planned to then manage with 22 cm (9 inches) of reinforced concrete.
The construction supervisor calculates 260 sqm * 8 cm (3 inches) = 20 m³ (additional) reinforced concrete * 150 € (85 per m³ concrete plus steel) = 3000 €, and sees no reason to adjust the floor plan.

Of course, the structural engineer has the final say, and small wall shifts don’t hurt anyone. But I also tend to avoid compromising on the floor plan just to save 3000 €. Looking forward to your comments on this.

This cannot be clearly answered because it depends on the compromises you have to make with the floor plan.

@WilderSueden That's correct, and how these compromises are valued is, of course, a very personal matter for me. So I'll ask differently: Is the assumption correct that the planning flexibility will cost me only about 3,000 € (approximately 3,300 USD)? Or are there other factors to consider (the total height of the building is expected not to be an issue regarding building regulations or permits)? Architect-2, for example, mentioned additional costs of around 15,000 € (approximately 16,500 USD) but usually works on different types of buildings.

You probably won’t have complete freedom in planning, but thicker ceilings can help compensate to some extent. However, since we don’t know exactly what you’re planning, it’s hard to assess. Fundamentally, I find it more reasonable to try to work with the physics rather than just throwing resources at a problem.

karl.jonas schrieb:

Is the assumption correct that the planning flexibility only costs me about €3000?

I agree with the opinion of @WilderSueden.
If you are only building an 8 x 8 meter (26 x 26 feet) structure, spending €3000 on “planning flexibility” is money wasted.
If a room can only be made wider by 500cm (197 inches) to 520cm (205 inches) through this investment, I personally still find €3000 far too expensive for that.
We had planning flexibility even without such an extra option and live in a spacious open-plan area.

WilderSueden schrieb:

Basically, I find it more reasonable to try to work with physical principles rather than throwing resources at a problem.

I fully agree with that!

karl.jonas schrieb:

Architect-1 plans the reinforced concrete intermediate slab to be 30 cm (12 inches) thick and has a lot of freedom in wall placement.
Architect-2 calls this "letting the forces walk around" and suggests that, for cost reasons, the load-bearing walls should be better planned so that a 22 cm (9 inches) reinforced concrete slab is sufficient.
The construction supervisor calculates 260 sqm (2800 sq ft) * 8 cm (3 inches) = 20 m³ (706 cubic feet) of (additional) reinforced concrete * 150 € (85 per m³ concrete plus steel) = 3000 €, and sees no reason to adjust the floor plan.

karl.jonas schrieb:

Is the assumption correct that the planning flexibility only costs me about 3000 €? [...] Architect-2, for example, spoke of additional costs around 15,000 €, but usually builds different types of buildings.

The latter explanation “is not sufficient” for me. When there is a cost estimate disagreement by a factor of 5, I assume the “truth” is closer to the higher figure.

WilderSueden schrieb:

Basically, I find it more reasonable to work with physics instead of throwing resources at a problem.

I generally consider "brute force" worthy of being the "Plan Z." Between the Neanderthal era and today, there should be several millennia of humanism (and it should not have been for nothing).

WilderSueden schrieb:

But we don’t know exactly what you are planning, so it’s hard to assess.

That can be fixed, that’s what good old external private messages are for...

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