Is it feasible to build a two-family house with parents / parents-in-law?

Even though all of this is a bit vague as a "forward looking statement": If you really want to build completely accessible for your parents, then you should add a good buffer. However, then some funding might become interesting. If it is only meant to be partially accessible, this is somewhat less relevant again.

So you can definitely build with 5000+ net income and >300k equity. Especially since the plot of land is a gift. How large you can build, you will have to see in 3 years.

@11ant The slope definitely requires a basement. However, it is moderate compared to what we have looked at otherwise. But probably the Fichtel Mountains are not the best comparison area for that :D We would like to build a prefabricated house in timber frame construction, and as far as I know, the basement will be masonry anyway.

For which advantages do you prefer a "prefab" house? Almost all of their manufacturers do not make their own basements. Due to the responsibility for fitting at the OKKD interface, be sure to have the basement delivered by the house manufacturer anyway (sometimes the manufacturers or the builders themselves come up with the idea to order the basement separately).

@Benutzer200 What size would be "well manageable" in your opinion? I completely agree that you can feel very comfortable even with less living space.

@11ant The slope definitely requires a basement. However, it is moderate compared to what else we have looked at. But probably the Fichtel Mountains are not the best comparison area for that :D We would like to build a prefabricated house in timber frame construction, the basement will be, as far as I know, built of masonry anyway.

There are three points you need to consider. 1. You are still really young chicks ;) . Then you can also comfortably work with 2% repayment. Especially against the background of good jobs. Example Interhyp, full repayer with a 30-year fixed interest rate - total security until the loan is repaid and at the same time rising salaries.

You can do quite a bit with the construction costs – it doesn’t have to be the highest energy standard or the golden faucet. 2. Hillside location You should involve a planner very early on. Maybe the basement will also become living space + utility room. Then the areas and thus also the costs are relativized again. And as I said, smaller houses also work, 10 sqm children's room, smaller bathroom, no ballroom as living/dining area, etc. 3. Parents / second apartment That’s an ace you still have up your sleeve. At least the additional costs for the apartment will be covered by the parents. In this respect, the operating costs for the house are more manageable (division of property tax, joint waste disposal, etc.). And of course, childcare is also already quite comfortably arranged.

Leave the classic basement, the parents' apartment goes, for example, into the [UG] with direct garden access. Or into the [OG] and you have [UG] with terrace and [EG]. Build 2.5 floors instead of 3.5. The basement is an additional cost driver because you are building on a slope. Split level is a keyword here.

Or into the upper floor and you have the basement with terrace and ground floor

But then an elevator or stairlift probably still needs to be factored in, because:

My parents need 85 sqm of living space, which we want to plan accordingly age-appropriate (barrier-free, etc.) right away.