How to obtain an exemption from the development plan?

I didn't mean the plot area, but the floor area on the upper floor. So on the sides, where the roof is still very low, space is lost because of the knee wall.

Yes. is right. If you care about space, wasted space in the house, then you would clearly plan a basement under your ground floor.
That way you avoid losing space under the house that could be used.

I didn't mean the plot area, but rather the floor area on the upper floor. So on the sides, where the roof is still very low, space is lost because of the knee wall.

That's even sillier. The area won't be developed, and that's that.

Girls, I thank you, even if it is sometimes a bit exhausting

Basement is out of the question, as space underground is even more expensive than above ground. It should also be cost-optimized.
(I’m already taking cover for the next verbal beatings)

You are really different.

You are really different.

No, he isn’t. Just contradictory.

And the underfloor heating will probably only extend up to this point, I suppose?

Yes, why would you want to heat the storage space as well?

If space on the property were that crucial, you would build with a basement.

In case the circumstances of the OP's story – apart from my memory of 11 posts – have escaped most of the discussants: the OP lives in a two-family house from the 70s on a property, behind whose garden side there used to be a road planned for a long time but in an uncertain manner. Now this road is to be completed and the OP wants – after a redrawing of the boundary line – to build a new building in this garden with a future direct street access, into which he will then move.