Floor plan first to live in, then to rent out, but how?

Someone regularly comes up with the idea. We also considered it once. In practice, you end up with either a bad single-family house or a bad two-family house. So far, I haven't seen a floor plan that does both well and uses space efficiently.

Because it simply doesn't work. The necessary, strict spatial separation of residential units in a multi-family house is diametrically opposed to the desired spatial unity in a single-family house. This is a conflict of goals that cannot be resolved, basically the squaring of the circle.

And in most cases, it’s nonsense anyway. Nowadays, people have children in their early to mid-30s, at least that applies to the clientele who can even think about building new homes. The children are out of the house by their early 20s (at the earliest), then you are in your early to mid-50s.
And then tenants are supposed to move in upstairs? In 45m²? The clientele that demands this size is not the kind you want living above you...
And what about the children when they come to visit?

There is already a clientele that is reasonable and needs little space. For example, young people who no longer want to live with their parents, but as a first apartment do not need or want to afford 100sqm. Middle-aged and older singles. Whole families, of course, are rather difficult to accommodate in 45sqm.

The problem is not only the strict separation or its avoidance. A single housing unit also has different requirements for the floor plans than the sleeping floor of a two-story housing unit.

We are currently renovating a two-family house, using it alone with the option to split it up again later. Either because we move out ourselves and then want to rent out the whole house, or just one residential unit. This is mainly a wish of my wife :) However, our new neighbors on both sides have handled it this way as well. There are also several multi-family houses on the street, so at least usage-wise it fits.

That means we have opened the stairwell, but made sure that on all (we have 3 – ground floor, 1st floor, 2nd floor) levels there is at least one bathroom with a shower (there was one before), kitchen connections are in place, a separate distribution box for the electrics, water meters for each unit, also a room on the open ground floor that can be used as a bedroom, etc...

I am still quite sure that we have forgotten something important. Also, this is of course an additional investment now. It starts with the distribution boxes but leads to an endless string of consequences – for example, with the doorbell system. Suddenly a simple doorbell is no longer enough, but you need an intercom system with 3 indoor stations, etc. The same theoretically applies to mailboxes, although these can be retrofitted better later, at least if you do surface mounting from the start.

For a new single-family house, however, I would never plan it like this. I would build it for the here and now just like everyone else wrote.

A single residential unit also has different requirements for the floor plans than the sleeping floor of a two-story residential unit.

For a new single-family house, however, I would never plan it that way. I would build it just like everyone else wrote, for the here and now.

A combination house as a both-in-one of current house and later house complicates not only the planning effort, but also unnecessarily increases costs in realization. All the pre-installations are also not stored in original packaging, aging-free, on ice. And the main problem is that these combination houses are a self-fulfilling prophecy: the extra effort burdens the agility of the assets. The extra money spent is missing, it burdens the economic ability to change property forever, and you therefore actually have to stay longer in the first house. A first house overloaded with universality expectations will then remain the only house, and that’s the vicious circle of the popular misconception "you only build once" :-(
So beware, whoever thinks too far around the corner, whether they are not shooting themselves in the back!

In short: whoever builds a current house and later house in one will automatically make the first house also the last one. For a young family, there is practically no heavier mortgage than this seemingly clever concept.

I actually have to contradict my predecessors here, as I know of 3 properties in my close circle of friends that have recently implemented this. In 2 of the 3 cases, the additional residential unit is currently even being rented out ("before the children"). In one variant, the upper floor consists exclusively of the 3 children's rooms + bathroom, which can easily act as a 2-room apartment. The entrance area can be quickly separated or reopened using drywall. In the other variant, 2 large rooms plus a bathroom are provided for the children, which are currently accessible via an external staircase and constitute a 40 sqm apartment. Also easily reversible.

And how practical is the solution in family life?