Smallest possible "mini-house" for residence

The main reason for the consideration is not that I find a tiny house so much cooler than a granny flat. It’s more about the property/garden. I am a big fan of ponds. I know they require maintenance too. But I am rather from the faction that likes “natural” ponds, and I think it’s great if I can observe how they develop over the years (I used to have a pond).

What do you need a pond for if— as you write— you are only at home to do laundry?

The question is: Does the laundry really get clean there?! ;-)

Why do you need a pond if you - as you write - are only at home to do laundry?

I am sometimes there for a whole day or even two before moving on. Let's say as an intermediate travel stop. It's nice to be able to relax by the pond. ;) Since the camper is then also at home, I actually only need the "house" for things I don't have mobile with me in the camper. And as long as a "residential house" stands on the property, no one can complain that I am camping on the property, which of course I would never do. Naturally, I then stayed overnight in the residential house, and the camper was just parked.

I travel a lot for business & usually spend my vacations traveling in the camper. The "house" would therefore only be used occasionally to do laundry, shower, charge the batteries of the camper, and to have an official residence. So 10m² would probably be sufficient. But do you get that approved or does building law recognize a "too small"?

If I were you, I wouldn't aim for a custom design, but rather place a small house "from the catalog" on a small plot. Or you can take a look here: and - in my posts, it is about a facility in Biblis (Bergstraße district, Hesse), where parcels can be leased at an excavation lake, whose usage differs in many ways from that in a community garden association: from caravan pitches to fincas, everything can be found there; in front of the gate on the country road stands a platoon of mailboxes (you can probably have packages delivered to the beach bistro). If the district code "Hessian Police" ;-) and the association of the place name with a nuclear power plant do not bother you, it is a quite nice location. The lessor is, as far as I know, the gravel mining company.

Garden. I am a big fan of ponds. I know they also need care. But I am more from the faction that likes "natural" ponds, and I think it's great.

but some random one in the middle of nowhere.

What you are describing is a recreational plot. Normally, you are not allowed to build in the middle of nowhere because there is no building land there, unless you have agricultural interest. Watching frogs is not part of that. To park a camper at night, you don't need a plot with a hut. You can also wash clothes more efficiently. And whether you have to build a hut for your hobby, simply to relax, is also questionable. Every municipality has recreational plots on the outskirts or in the forest. You can buy them for cheap money. Everything included, mostly with a septic tank, but running water and electricity. Some can even be registered as permanent residences. Where are you registered now?

For registration as a residence, you don't need a house. Just a house number. Plot within the inner area and a house number. Nothing more. Apply for a house number at the regulatory office of your municipality if you don't have one yet. It costs around 35 euros. Then you can register at the residents' registration office and that's it. You could also put up a mailbox for the mail.

Legally, it is like this. Depending on the federal state, you can then build without a permit, e.g., a garage with 50 sqm and an eaves height of 3 m. You could put a washing machine and refrigerator etc. in there. You can also sleep inside or in the camper.