Conversion of a split-level house into two apartments

In search of help, we need a little (or more) input.

Shortly before retirement, we are faced with a familiar problem. The children have moved out of the house, which is now too big in its current form. Our son would like to come back and occupy the upper part of the house, provided that a separate apartment can somehow be created. We cannot use the granny flat because it is occupied by grandparents. So, somehow we need two separate apartments in addition to the granny flat. We have already thought back and forth, but we are not making progress due to the split-level construction.

We understand that this cannot be done for €10,000 – 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 is also suitable for old age, the location is unique, unobstructed directly in nature, and the building fabric is excellent. Our construction company preferred to use an extra reinforcement back then and did an excellent job.
Here are the further details:

Plot size 650 sqm
Slope yes
Edge development: Our garage is a boundary development and on the entrance side we could theoretically extend onto the neighbor’s garage with terrace in the same form. This was also recorded in the land register at the time.
Number of people Granny flat 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 the dining/living room, bedroom, bathroom, possibly guest WC, reasonable wardrobe (we have a lot of dirty clothes because we spend time in nature). Nice to have would be a backup kitchen and dressing room. But I’m realistic – not possible due to the square meter count. ... Does an elevator make sense for old age???
Home office: Still about 2x per week for the next 8-10 years. We will probably have to arrange somehow...
No overnight guests
Fireplace yes! We have one and since we manage forest ourselves, it’s a no-brainer.
We currently have a double garage. If it has to give way for living space, then so be it.
2nd floor: Cooking, dining, living, sleeping, bathroom, children’s room, permanent home office space, wardrobe, guest WC?
Preferably the living rooms facing north with a view of nature. On one level without many stairs for old age. (Tear down the rear gable and bring it to one level?) Unfortunately, this was not taken into account in the house planning. Until now, we have lived wonderfully and very generously according to our needs – is there even THE SOLUTION so that everyone here will be happy?
We thank you in advance for all input and ideas.

Our son would gladly come back and live in the upper part of the house, provided that a separate apartment can somehow be created.

For how long? There are two of them. I do not see the attic as a long-term solution for 4 people; it doesn’t seem to meet the needs at first if you want to accommodate 3 bedrooms, a kitchen, and a living room.

Number of people in the granny flat 2, 1st floor 2, 2nd floor now 2 later with child(ren)
Space requirements: 1st floor: separate kitchen with small dining area, space for a large dining table in the dining/living area, bedroom, bathroom, possibly guest toilet, reasonable wardrobe (we have a lot of dirty clothes because we are out in nature) nice to have would be a backup kitchen and dressing room. But I’m realistic – not possible due to the square meters...

So basically the current state of the middle level. I do not currently see the space requirement as reducible, although it would be possible to create a connection from the utility room at the top of the plan to the staircase with a separate entrance for the attic.

We can’t go into the granny flat because it is inhabited by grandparents.

How old are the grandparents?

Just before retirement

Home office: Approximately 2x per week for the next 8-10 years.

How should your age be understood: just before retirement with 8-10 years of home office?

Our garage is a boundary development and theoretically we could attach the neighbor’s terrace on the garage entrance side in the same form.

Is it a townhouse? Semi-detached house? Boundary development usually excludes living space unless it is one of these.

Does an elevator make sense for old age???

If one cannot manage steps, possibly. However, there are other options. Why do you need an elevator if you want to separate? For the 5 steps to the intermediate level?

I am actually missing the site plan here, i.e. the entire property. How much space and area is there on the left, right, etc., so that you could even generate parking spaces or another access?

The age of the residents is not clear to me at all: if you are just before retirement, you would be around 65? Then the grandparents would be around 85? Then realistically, you could wait a few more years and then simply move into the ground floor, with all the consequences, i.e. downsizing, and give the upper and attic floors to the son, whereby the entrance situation could possibly be modified again via the utility room or workroom.

How many outdoor stairs are there to actually reach the ground floor?

Here is a first idea, hoping that I have read the plans correctly:
Basement apartment remains unchanged

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


The role of the conservatory is not entirely clear to me yet. Could the home office space go there?



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

Edit: Sorry, there was a wall missing between the basement stairs and the top-floor apartment stairs.

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Just a tip: 3 apartments = multi-family house. Is that even approvable with you? Can the necessary parking spaces be created?

Not that you plan wildly (I prefer to stay out of that) and later it turns out that according to the development plan only 2 residential units per building are permitted.

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

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