Planning a Granny Flat - What to Consider?

Hello everyone,

we are still somewhat "planning" the house and are currently considering a granny flat (approx. 50 sqm) in the attic.
For us, the granny flat is to be located in the attic and accessible separately via an outside staircase.
Things like coordinating sanitary connections in the attic with the ground floor, etc. already come to mind, but there are surely many other things to consider (supply lines, electrical circuits, subsidies, noise, etc.).

It would be great if someone could share experience regarding special features in the planning or later living with a granny flat.

Thank you very much

Nobody with experience?

If controlled residential ventilation is planned, it must be separately controllable.

Additional heat quantity meter for the heating.

Water and electricity meters.

And pay attention to soundproofing; I would be annoyed by strangers whose footsteps I can hear.

Observe room height, at least 2.4m.

A second KfW loan is possible.

For taxes, you can specify the apartment; back then we declared 100k, that was 50k KfW and 50k additional loan. Additionally, everything like outdoor facilities, but only a portion of that and your work as a janitor.

We bought the kitchen and depreciate it; however, something changed this year.

That’s what I can think of quickly; it’s best to go to a tax advisor.

Are you sure about that? Usually, people build a house to have peace and quiet. Then someone is trampling on your heads and watching you sunbathe etc. from their apartment... Not my thing.

Parking lot, the regulation is different here. For us, up to 50sqm one parking space is required, and over 50sqm two parking spaces.

Are you sure about that? Most people build a house to have their peace and quiet. Then someone is trampling over your heads and watching you from their apartment while sunbathing, etc... That wouldn't be for me.

Currently still thinking it over. However, the rooms would already be there for us anyway (keyword KFW 55 for 2nd residential unit). The granny flat would be spatially and visually on the other side of the main garden, if we wanted to rent it out. The entrance would also be separate.