Conversion of a two-family house into a duplex with complete renovation

Hello everyone, we already own a house from the 1950s. A complete renovation is urgently needed.

Our current plan is as follows: to convert/expand the existing two-family house (basement, ground floor, first floor, attic) - if possible - into a semi-detached house. Two separate semi-detached halves are to be created. Whether this is possible and economically sensible due to the existing staircase, we cannot yet assess. Is there anyone who has done such a project before or has ideas/suggestions? So far, I have found nothing online that helps us further.

We want to move into one semi-detached half (2 adults, 2 children), and grandma into the other half (she may need less living space). Separate front doors, terraces, and garden are important to us.

Here are current plans (we own the approximately 800 sqm plot 15, the red building does not exist):

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Your floor plans are countless and the small site plan excerpt is not really usable. The floor plans also do not seem to be from the original year of construction (rather from the attic conversion?). The floor plans apparently confirm a suspicion of (I suspect that old and new brick formats were mixed). Why you keep fixating on the idea of turning the granny flat into a semi-detached house, only the gods know. The extension potential of the current house certainly does not support this concept idea. Possibly, an upper house entrance for the unit "upper floor & attic" could be realized. What about the shed/stable/laundry room, what role should this outbuilding play in the future and could it possibly be removed?

Give up your stinginess with background information, then you can be helped.

What is still missing:
- Photos of the house, masonry, infrastructure, roof, etc.
- the repeatedly requested information on budget, requirements, etc.
- justification why it has to be these very specific solutions

I also have a 1953 house here. Of course you can live in it, of course you can renovate it, but even a basic renovation is more expensive than a new build and a reasonably energy-efficient house is out of the question, not to mention a passive house. Renovation while the house is occupied? No way.

- Reason why it has to be these rather special solutions

I think, at its core, it is simply about a separate front door for the "grandma" (so that it doesn't disturb when she comes home very early from the disco ?). One thing I can guarantee is this: that grandma will feed the dear kids chocolate at her own discretion, separate front doors will not prevent that.

I think, at its core, it's simply about a separate front door for "Grandma" (so it doesn't disturb when she comes home very early from the disco ?). One thing I can guarantee: that Grandma will feed the dear kids chocolate at her own discretion, separate front doors won't prevent that.

I meant it more globally and galactically, like why the house should be completely renovated and expanded instead of building a new house – if you have to move out temporarily anyway, it doesn't matter whether you move out for two or twelve months.

I'm a bit fascinated by the consultation resilience, asking the same question every year and expecting a different result – after all, the initial situation has changed a little by now. Now, with the photos, detailed information, etc., then one can say something.

Why always so unfriendly? Private problems? I kindly ask for no further replies or "tips" from you, thanks.


Yes, you're right, the initial situation has changed insofar as the 1st floor is no longer occupied and our grandma (who lives on the ground floor) is open to all suggestions/variants. Since she still lives in the house, it does make a difference for her whether she would have to move out long-term (in case of demolition and new construction) or only for 1-2 months. The energy standard to which the house (possible semi-detached house) can be brought in case of core renovation/rebuilding also plays a role. It should become a low-energy house; passive house is probably impossible in renovation. Basically, for us it is first about clarifying which floor plan variants would be possible with the existing house. Then we would weigh up a cost comparison between new construction and renovation as well as energy standards, etc. If a semi-detached house is not possible from the outset or no house with a separate ground floor (entrance via 1st floor is not an option), it will not be a renovation anyway. For KfW, renovation would of course be great.
The shed does not play a role here and can, of course, be removed.
Unfortunately, there are no further plans of the house than the ones already uploaded :) Or which plan exactly do you mean?
I will take some photos of the house tomorrow, but I don’t think it’s that important for the floor plan planning yet, right?
Thank you very much!