House construction on narrow land? 3-family house already exists

Thank you for the message.
So an architect said that in Hamburg 2.5 m to the respective property boundary would also be possible.
That would then be a good basis.
With 4.5 m I could imagine quite a bit, but with only 3.5 meters rather not.
Especially since with 4.5 m you can also plan many windows.
I have already created a floor plan as a layperson, but it is certainly optimizable.
A conservatory would also be added to the living room.
For my ideas, I am only missing 0.50 meters in width.

Do I understand correctly that this is about parcel 684? Where exactly is the width of 9.5m? To me, it looks on the site plan as if the property gets wider towards the south...

Which rooms are supposed to be accommodated? Office? Children's room?

I'd like to play around a bit

In Hamburg, the boundary distance is only 2.50m, but the roof overhang must not extend beyond 50cm. So 4.5 m remain. However, I would try to get permission for one-sided boundary development. Isn’t there also a building line to be observed?

It concerns the plot 684. It actually only becomes somewhat wider towards the end. My current measurement actually shows 10.80m towards the end. That is quite pleasing. Inside it should be as follows: On the ground floor: Living room with open kitchen (at least 50 sqm) Large bedroom Guest WC Upper floor: Bedroom Large bathroom Storage room, does not have to be big Large roof terrace towards the end of the plot Basement: 2 large rooms Possibly small kitchen and WC with shower The house can also become wider towards the end, just like the plot. Looking forward to your design!

There is a completely different hurdle - no rear development is permitted in the development plan, the building line only includes the front, existing development. Ergo, application for amendment of the development plan (no legal claim!), so that it is even addressed. If at all, only with neighborhood consent.

If no supplementary development plan exists ... a long way for a house width of 4.5m ...

Best regards
Dirk Grafe

There is a completely different hurdle - the development plan does not allow any rear development at all, the building line only covers the front, existing development. Ergo, application for amendment of the development plan (no legal entitlement!), so that it is even addressed. If at all, then only with neighborhood consent.

If no supplementary development plan exists ... a long way for a house width of 4.5m ...

Best regards
Dirk Grafe

Oh dear, I was not aware of that at all.
However, there are indeed houses in the second row on this street.
I hope it is somehow possible.
Because such a plot would cost me another 150,000-200,000 euros here in Hamburg.
Then my dream is shattered.