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

What is there to downsize? I live on the ground and upper floors, and the basement is just storage space. Somehow, I find that the wrong approach. I obviously did not mean the load-bearing interior walls here – for our small house, these are only the exterior walls and the stairwell walls. The rest is non-load-bearing. I am still not 100% convinced about the basement – whether 15k or 50k makes a significant difference to me – even if it might hurt to bury 15k. It would hurt more to reduce high-quality living space or to cut the controlled residential ventilation than to not build a basement.

I don’t want to convince you here to be pro-basement, because you’ll need your budget later anyway to cover other things. This is just the beginning, without really having started yet.

Well, the building services could at least go in the basement, washing machine, freezer, etc. You can theoretically just run down the stairs for now, but screed has to be installed. Light shafts, at least small ones, should be included. Everything else (electricity / heating / drywall walls / doors) you can theoretically do later. However, I would already provide for and plan certain preparations now and have them laid. The Energy Saving Ordinance is a problem, possibly a door has to be installed in front of the stairs, and the ceiling will have to be insulated. I’m telling you, if it actually costs 35k more in that area, the basement with that house size is so worth it! There’s so much stuff you have and it definitely has its justification, but you also like to have it tidied away sometimes.

I’m telling you, if it’s actually around 35k more

It’s not just 35k but a total of 50k more. I don’t think it will be that extreme. Our previous basement offer from the general contractor was 44k including everything – but only with "sand soil". However, that included excavation of three meters – now it’s only 1.50m.

Our general contractor is on vacation now and will write us a precise offer with and without basement shortly thereafter – then we will also know to what extent we can use the excavation for filling the garden.

Our new development area will probably be finished by 01.10, so we can start right away. All applications for house connections as well as, very importantly, construction electricity are or are being processed.

We lived for 38 years in a house whose basement had no screed, whose raw walls were painted white, and where electrical wiring was surface-mounted, with one basement ceiling lamp per room. It didn’t bother me at the workbench, nor the preserved cherries and pears on the shelf next to it.

A partial basement will bring no savings here, not even a small one. Just take the ground floor from #52
https://www.hausbau-forum.de/attachments/Reihenendhaus-mit-gue-in-Eigenregie-bauen-336541-1-jpeg.36757/
with the following modifications:
Mirror the wall between the stairs and the wardrobe along with the door on the other side of the stairs # extend the kitchen wall up to there # omit the partition wall between the WC and the wardrobe. The utility room is then at the bottom of the plan, and a multipurpose room at the top of the plan, divided with slats or not divided at all. The door to the utility room will possibly be a classic interior door, the door to the multipurpose room you take like as an attic closure as an inexpensive DIY store balcony door. No window under the terrace, so that there is no light shaft in front of the sliding door upstairs.

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

Basically, it is as 11ant writes. But I wouldn’t do it exactly like that today anymore.

If it were mine, I would spend the money on the floor slab including floor insulation. That means a concrete slab, bitumen sheeting insulation, styrofoam, screed. This way you have proper insulation against cold from below.

Then the structural engineer will probably come and demand walls or columns at certain points. These have to be installed. I would do only what is necessary. Once you know that, you choose a 10 to 12 sqm room to section off for the technical equipment, ideally in such a way that the pipes are short. I would separate this room with drywall. Since the heating is inside and insulated from below, the room will be warm. Put the washing machine in there along with all connections.

I wouldn’t install heating in the rest of the basement but would provide connections for a possible extension at the heating. (What kind of heating will even be installed there?)
The same goes for the electrical system. Only the stair light and possibly a lamp for the path to the HAR (house utility room) should be switched together via a two-way switch. More lights or sockets can be retrofitted – surface-mounted cables don’t bother in the basement either.

I would coat the screed with a sealant. We also did that in the garage so it doesn’t get dusty and dirt doesn’t penetrate the concrete. It’s inexpensive and quickly done with a paint roller.

Done. If there is still some extra cash left somewhere, you can plan a light well. But that’s already a luxury and not necessary.

done. If there is still a miniEuro left somewhere, you can plan a light well. But that is already luxury and not necessary.

What would you still use the basement for, Katja? The garden is too small for a slope for a second emergency exit. Because I would probably try to place the rooms in such a way that you manage with 3 floors. This is all a calculation example. Sure: with the option of a finished basement you can probably sell the house better, but if that means restricting your lifestyle because the loan payment becomes too high, then I would also consider what you are borrowing money for something you don't need. And honestly: the attic is cozy. Much nicer than a basement. If the money is there, yes, then! The best thing would probably be to put an underground garage in there Unaffordable in this constellation.

Then the structural engineer will surely come and require walls or columns at certain points.

Not necessarily. 7 meters external dimension can still be easily managed without load-bearing walls.