Divide the plot in half or change it from a single house to a duplex?

Or in other words:

Assuming one buys a large plot of land,

Large is relative.

on which one could easily build a semi-detached house or a townhouse.

At 100% development? That reads as if a child says: I will build a huge princess castle in my parents’ garden because there is still space.

However, the building permit only allows single-family homes.

Then that's how it is. But a single-family house often can also have a granny flat...

Can one realistically achieve a change, or will it be difficult?

Why should the municipality change something for you that took several years of examination to establish?

Will it be easier to divide the plot and make two or three out of it, each with single-family homes?

See above. Why should the farmer simply be allowed to do what the king has determined? Certainly, some things are possible, as Escroda also writes, after all, we live in Germany without a king and not in the Middle Ages and so on, but that only in exceptional cases. For you, it just sounds like costs are intended to be saved because you can’t financially afford the plot.

Or will this fall victim to the same difficulties?

Victim? Why victim? Fortunately, there are rules.

The statement is that currently only detached houses are allowed to be built. There are multi-family houses in the neighborhood, but the houses directly around the plot are all detached houses. I would of course like to provide more facts, but unfortunately, I do not have them. [...] The plot has been vacant for several years.

That sounds more like you are mixing up detached houses and single-family houses, and secondly, as if you were talking about a §34 area (where there are no development plans).

Is a development plan then permanent? So, if a plot is only to be built on after, for example, 20 years, does the development plan from 20 years ago apply?

If it has not been changed in the meantime, yes. A development plan is valid until it is changed or repealed.

If the sum of the distances must be observed, but otherwise one can agree bilaterally, could one then build the houses almost like a semi-detached house together, as long as there is enough distance maintained on the other side? But one is not allowed to build a semi-detached house on these two plots together? In other words, buy two plots and put a semi-detached house on them (shared wall basically on the property boundary) to create more space at the far boundary?

1. I was talking about distances and distance sums between two houses – not two houses to third parties. 2. No, a semi-detached house may only be built on two adjacent D or E/D plots or on one plot. On two adjacent plots that do not permit D or E/D, attaching one house to the other side is not allowed (except sometimes in §34 areas in old village cores). 3. You may always maintain more than the required distance – it is a minimum distance. We have fully understood your crazy idea in all its facets – it doesn’t work, no matter how oddly and crosswise you ask about it.

Hello everyone.

Thank you very much for the many pieces of information. There were indeed a few misunderstandings on my part. I had understood the statement to mean that if, according to regulations, you must maintain a 2m distance on each side from the neighboring property, you can agree with one neighbor to reduce the distance to 0.5m but then must maintain 3.5m on the other side. Because the total (2m on the left, 2m on the right, so 4m) must remain. If that were the case, you would gain much more space on the free side with 3.5m.

I also did not say that I am making any demands on the municipality. So no one here should feel attacked if I ask something to gain more information about what is possible and what is not. A development plan may have made sense 20 years ago and today the world looks different and a change might be (also from the municipality’s point of view) more sensible. Situations do change. That is why my question.

But then I basically have most of the information and thank you for your help.

Why should a municipality update a development plan just because the building style is different now? The setback distance has (if I am not mistaken) something to do with fire protection as well. You can't just split the distance to the left and right however you like. Neighbors can agree among themselves that one builds closer to the boundary. Accordingly, the other must keep a greater distance.

I understood the statement to mean that if, according to regulations, you must have a 2m distance on each side to the neighboring property, you may agree with a neighbor to reduce the distance to 0.5m on one side but then have to keep 3.5m on the other side. Because the total (2m left, 2m right, i.e. 4m) must be maintained.

No, it is about the total distance sum between house A and house B – what is negotiable is only how much of that is fulfilled on the section between house A and the fence between properties A and B, and the rest between the fence and house B must then add up to the total again.

A development plan may have made sense twenty years ago, and today the world simply looks different and a change might be (also from the municipality's point of view) more sensible. Situations do change. That is why my question.

A development plan from twenty years ago even has a higher chance of being changed than one from sixty years ago: because in the latter case, of eighty-six building plots, only three remain undeveloped, and it is more sensible for the municipality not to have to rebuild the entire buffet along with the Christmas tree again for those three guys. The older potentially the more open one is to deviation requests. But as I said, your sparse information sounded rather like no development plan anyway.