Build a terraced end house with an additional unit (GÜ) on your own

You can't use the topsoil for backfilling anyway. I would buy the basement. It's practically already one. 2.40m strip foundations = ideal basement height. You can leave it unfinished for now. Then you only pay for the stairs and the floor and the necessary supporting columns additionally, right? Have a few empty conduits laid down... In case of sudden wealth you'll be happy, otherwise it's storage space for comparatively little money.

We will have it calculated. However, that quickly adds up to another 30-40k, as we would also move our technology from the attic to the basement - but then the attic must also be developed to a higher standard, which causes additional costs. We have planned some buffer - but not 60k, which the basement with additional work will cost in total.

However, then quickly another 30-40k add up, since we would then also put our technology from the DG into the KG - however, the DG would then also have to be upgraded to a higher standard, which causes additional costs again. We have planned a buffer - but not 60k, which the basement will cost in total with additional work.

Technology downstairs would be nice. But the DG isn’t going to get more expensive because of that, is it?! Unless you give up the in my opinion unnecessary dormer and save yourself the money for the additional base slab.

Lowering the technology would be nice. But the attic wouldn't be more expensive because of that, would it?! Unless you skip the, in my opinion, unnecessary dormer and save the money for the additional base slab.

Then alternative roof windows also cost money - and the dormer, however, costs "only" 7,000, so the savings wouldn't really be that high.
We could scrap the controlled residential ventilation - that's around 15k. Then we would have saved something.

Remove insulation and controlled residential ventilation – it's almost like the basement already.
You can't calculate anymore like at the beginning. Basically, you HAVE to build the basement. The money for the walls and the structural engineering is lost either way. Filling it with gravel now so you don't need electrical outlets is almost idiotic. Yes, okay, you still need a staircase – but it doesn't have to be made of gold like the others. A floor slab or a ceiling will be added. Okay, that has to be paid for as well. Otherwise, I don't see any major additional expenses now. No one is forcing you to lay tiles, build walls, or install a lighting system down there. And if you’re really in trouble, something like that can still be done later.

Roof gone and controlled residential ventilation gone - it's almost like the basement already.
You can't calculate like at the beginning anymore. Basically, you HAVE to build the basement. The money for the walls and the statics is lost anyway. Filling the thing with gravel now so you don't need sockets is almost stupid. Yes, okay, you still need a staircase - but it doesn't have to be made of gold like the others. A floor slab or a ceiling will be added. Okay, that also has to be paid for. Otherwise, I don't see any major additional expenses now. No one is forcing you to lay tiles down there, build walls or install a lighting system. And if it gets you, something like that can be done later.

If only it were always as easy as you described...

No attic and no controlled residential ventilation – it's almost like the basement already.
You can’t calculate the way you did at the beginning anymore. Basically, you MUST build the basement. The money for the walls and the statics is lost either way. Filling it now with gravel so you don’t need any sockets is almost stupid. Yeah, okay, you still need a staircase – but it doesn’t have to be a golden one like the others. A floor slab or a ceiling also needs to be added. Okay, that also has to be paid for. Otherwise, I don’t see any major additional expenses now. No one forces you to lay tiles down there, build walls, or install a lighting system. And if you feel like it later, such things can still be done afterwards.

To pick up your idea of a stripped-down basement once again: what can be omitted if the basement is used solely as a storage space and technical room?

Do I absolutely need a screed and underfloor heating? Do I have to build interior walls necessarily? But what about the Energy Saving Ordinance then? Wouldn’t the cold from the basement come upstairs on cold days?

What do you think?