Planning with an older development plan

In the case of the OP, the problem is more a misunderstanding, the belief that the young development plan is old, just because the knee wall is named and thus the exterior wall on the eaves side is height-restricted – the idea of “exploiting all deviations” I personally find somewhat presumptuous, without considering that a city villa is not the standard for everyone. It is then personal bad luck to have to adapt sometimes. Knee wall houses have their justification; even the attic should be a blessing for many to be able to generate additional living or storage space.

I am aware that there are significantly older development plans. However, in the newest development plans in the municipality, hardly any specifications are made anymore. There are flat roofs, bungalows, city villas, etc. In this respect, I could imagine that the older plans are not seen as rigidly anymore. For example, if you build on the ground floor without increasing the number of floors, you could add the “wasted” 30cm onto the knee wall. It is hardly noticeable from the outside and the knee wall would almost be doubled.

however, hardly any specifications are made anymore. There are flat roofs, bungalows, city villas, etc.

Yes, there are also such areas.
Development plans are made to structure small (residential) areas so that many things fit into an overall picture—not to annoy builders.

In your/this case, it is not about other residential areas but about protecting your future neighbors, that is, exactly this course of the street.
Where should the end of the exhausted limit be?
Ultimately, you as a future builder are also protected so that, for example, no four-story apartment building is placed in front of you.
In principle, the public interest always counts, not the personal one.

However, hardly any requirements are made in the latest development plans in the municipality.

That may be the case for this specific municipality, but generally, this is not the case, and it definitely isn't here. We still have a relatively generous plan; I doubt that the next new development area will be as generous. The reason is... surprise... someone who pushes everything to the limit and wants to build things that were never intended and don’t fit in. As Yvonne said, a development plan primarily protects the neighbors from your misdeeds. That some regulations arise more from doubtful benefits on the green wish list (permeable paving, retention cistern, green carports, ...) does not affect the regulations regarding the building structure.

Yes, you do gain storage space. Especially in children's rooms, you can wonderfully install shelves or cabinets there.

Yes, I see it the same way. My daughter's room is a great children's room and has about 50cm knee wall. Single-layer cube shelves fit under the beams. But in those and in other shallow boxes and such, she has most of her toys and on top her Toniebox, her football, a small plant, etc. Without this space, her room would be tiny.

I am aware that there are significantly older development plans. However, in the latest development plans in the municipality, hardly any specifications are made anymore. There are flat roofs, bungalows, city villas, etc. In this respect, I could imagine that with the older plans, things are no longer seen quite so rigidly.

There are reasons for culture to relate development plans to areas rather than uniformly across the municipality based on years of construction. The principle of equal treatment in discretionary decisions is also a high value. And no one says that your exemption requests are excluded from being granted – the (in my opinion, however, exceptional) example from even gives cause for hope from your point of view. I am merely saying from my experience that the tolerance of municipalities regarding knee wall height, roof pitch, and roof overhang – especially in combination – is particularly thin-skinned because this significantly affects local color (and that I see the hardest unwillingness to negotiate there).

Development plans are made to structure small (residential) areas so that much fits into an overall picture – not to annoy builders.

And even in the Insalata-mista development plan areas, there are builders who get annoyed – because they wanted a Bauhaus and their building plot lies beyond the dumpling line in the "Tuscan quarter" WA5 ;-)

For example, if one builds on the ground floor without increasing the number of floors, one could add the "given away" 30 cm to the knee wall. Hardly noticeable from the outside, and the knee wall would be almost doubled.

Yes, I feel like I’ve been saying this since the exodus from Egypt: that the individual, explicit regulation of the knee wall height is irrelevant for neighbor protection and the ensemble image of the development area, as it captures the position of the ground floor/upper floor ceiling rather inadequately in principle, and that public and neighborly interests would be sufficiently and appropriately considered by the specifications for eaves height alone. But I can’t run for municipal council everywhere to influence this ;-)

If in your case it is so that a modern ground floor instead of a podiumed raised ground floor would offer a potential for 30 cm height redistribution in favor of the knee wall, then my advice would be to cite this circumstance in the justification for the exemption request. Under these circumstances, I would consider 100 cm knee wall a reasonably achievable goal – and if you add a waiver of roof structures (and also package this in the justification), even 120 cm. Your exemption request must be acceptable to the municipal council without loss of face vis-à-vis neighbors who are treated legally without exception. No municipality and only very few council members want to annoy building applicants.

However, municipalities are affected to varying degrees by newcomers from other architectural taste regions and have therefore developed their defensive attitudes towards "excess users." That's why I said, inform yourself as best as possible about which sanctity level is attached to which individual restriction from which history. My experience is that the more rural the specific Hintertupfing is located, the more seriously the non-mixing of Bavarian / Franconian / Swabian building culture is taken, and the "saupreißische mog mer fei scho garned." (roughly: "we certainly don’t want the darn Prussians.") Similarly, there are certainly similar cases with the Schleswig and Viking cultures ;-) and here in the Rhineland, the Counter-Reformation remains a perennial sore spot in many areas ...

If this is the case for you, that a modern ground floor instead of a raised piano nobile would offer potential for 30 cm height redistribution in favor of the knee wall, then my advice would be to also include this circumstance in the reasoning for the exemption request. Under these circumstances, I would consider 100 cm knee wall desirable for success – and if you waive roof extensions (and also include this in the reasoning), even 120 cm.

Thank you, that’s roughly how I had imagined it. In my opinion, all three wishes could also be argued with the (increasingly important) topic of climate protection (even though building a single-family house is not climate-friendly per se).
A higher knee wall allows me to fit my spatial program on less sealed area in square meters, a roof without roof structures with an ideal inclination to the sun for the highest yield of the photovoltaic system, more roof overhang, more roof surface (photovoltaics) and at the same time better shading of the façade in summer.

Now, to come back to my first question: Should I first discuss my wishes (including arguments) with the municipality, come directly with the building application, or hire an architect for a preliminary building inquiry?