ᐅ Conversion of a split-level house into two separate apartments

Looking for some help, we need a little (or more) input.

Shortly before retirement, we are facing a familiar problem. The children have left the house, which is now too large in its current form. Our son would like to come back and live in the upper part of the house, if a separate apartment can be arranged somehow. We can’t use the secondary apartment because it is occupied by the grandparents. So, in addition to the secondary apartment, we somehow need two separate apartments. We have thought about it back and forth but can’t really make progress because of the split-level design.

We understand this won’t be solved with just 10,000 € (around $11,000) – better to bite the bullet now and then enjoy the house and surroundings in retirement.
Selling is actually not an option, although it would be the easiest: we feel very comfortable here, the infrastructure still suits us as we age, the location is unique, protected from future development directly in nature, and the building quality is great. Our construction company used more reinforcement than required and did excellent work.
Here are the additional details:

Plot size: 650 sqm (7000 sq ft)
Slope: yes
Bordering development: Our garage is built on the property boundary, and on the entrance side we could theoretically extend onto the neighbor’s terrace in the same style. This was also recorded in the land register at the time.
Number of people: Secondary apartment 2, 1st floor 2, 2nd floor currently 2, later with children
Space requirements:
1st floor: separate kitchen with small dining area, space for a large dining table in dining/living room, bedroom, bathroom, possibly guest toilet, reasonable wardrobe area (we have a lot of dirty clothes because we spend a lot of time outdoors in nature). Nice to have would be a backup kitchen and dressing room, but I’m realistic – probably not possible given the square meters. ... Would an elevator make sense for old age???
Home office: About twice a week for the next 8-10 years or so. We will have to figure something out…
No overnight guests
Fireplace: yes! We have one and since we manage our own woodland, it’s easy to run.
We currently have a double garage. If it has to make way for living space, then so be it.
2nd floor: cooking, dining, living, sleeping, bathroom, children’s room, permanent home office space, wardrobe, guest toilet?
Preferably living rooms facing north with views of nature. On one level without many stairs for old age. (Tear down the rear gable and level it out?) Unfortunately, this was not considered in the original house planning. So far, we have lived very well and generously for our needs – is there even THE SOLUTION so that everyone here will be happy?
We thank you in advance for all input and ideas.

Problemchen schrieb:

Our son would like to come back and live in the upper part of the house, if somehow a separate apartment can be arranged.

For how long? There are two of them. I don’t see the attic as a long-term option for four people; it doesn’t seem to meet the needs if you want to fit three bedrooms, a kitchen, and a living room.

Problemchen schrieb:

Number of people in the granny flat: 2, first floor: 2, second floor currently 2, later with child(ren)
Space requirements: first floor: separate kitchen with small dining area, space for a large dining table in the dining/living area, bedroom, bathroom, possibly guest toilet, decent cloakroom (we have a lot of dirty clothes because we are outdoors a lot). Nice to have would be a backup kitchen and a walk-in closet. But I’m realistic – not possible due to the square meters...

So basically the current state of the middle level. I don’t think the space requirements can be reduced at the moment, although you could create an access from the utility room at the top of the floor plan to the staircase with a separate entrance to the attic.

Problemchen schrieb:

We can’t use the granny flat because it is occupied by the grandparents.

How old are the grandparents?

Problemchen schrieb:

Just before retirement.

Problemchen schrieb:

Home office: About twice a week for the next 8-10 years.

How should we understand your ages: just before retirement with 8-10 more years of home office?

Problemchen schrieb:

Our garage is built on the property boundary, and theoretically on the entrance side, we could extend onto the neighbor’s terrace connected to the garage in the same form.

Is this a townhouse? Semi-detached? Building on the boundary usually excludes living space, unless it is one of those types.

Problemchen schrieb:

Does an elevator make sense for old age???

If you can’t manage any steps, possibly. However, there are other options. What exactly do you need an elevator for if you want to separate the living spaces? For the five steps to the intermediate level?

I’m really missing the site plan here—meaning the whole property. How much space and area is there on the left, right, etc., so that parking spaces or an additional entrance could be created at all?

The ages of the residents are unclear to me: if you are just before retirement, you would be around 65? Then the grandparents would be about 85? Realistically, you could wait a few more years and simply move to the ground floor, accepting the usual consequences like downsizing and giving the upper and attic floors to your son. The entrance situation could then possibly be modified again via the utility room or workspace.

How many external stairs are there to reach the ground floor at all?

Here is an initial idea, hoping I have read the plans correctly:
The basement apartment remains unchanged.

Upper floor: The wardrobe will be shared. The family upstairs can also install a narrow hook board at the height of the stair landing.

I am still not entirely sure about the purpose of the conservatory. Could the home office be located there?

If it is possible to close off the open space and add a ceiling, I would do that. Then the office could be downstairs in the conservatory, and upstairs either the living area could be larger or, even better, a large balcony could be added.
The washing machine would have to be integrated either into the bathroom upstairs or, if necessary, into the kitchen.

Edit: Sorry, there was a missing wall between the basement staircase and the attic apartment staircase.

Just a tip:
3 apartments = multi-family house. Is that even allowed with your local authorities? Can the required parking spaces be provided?

I just want to make sure you’re not planning wildly (I prefer to stay out of that) and later find out that, according to the zoning plan, only 2 dwelling units per building are permitted.

K a t j a schrieb:

Edit: Sorry, there was a missing wall between the basement stairway and the stairway to the attic apartment.

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Thank you very much for the quick response. That was actually our approach as well. The conservatory is currently being used as a workspace and music room. A ceiling can be installed there without much difficulty to create a separate apartment on the upper floor.