Floor area ratio; § 19 para.4 Building Use Ordinance - experiences?

Wrong. If a municipality designates a residential area, it must be treated as such. The municipality does not have completely free rein. QUOTE:
"Deviating regulations in the development plan (§ 19 paragraph 4 sentence 3 Federal Land Utilization Ordinance)

In the development plan, deviating provisions from the regulations of § 19 paragraph 4 sentence 2 Federal Land Utilization Ordinance can be made, e.g. higher or lower percentage rates, higher or lower capping limits than the floor space index of 0.8. The deviating provisions must be justified from an urban planning perspective...
Provisions must be made by text (§ 2); examples:
On the parcel of land ..... the stipulated floor space index of 0.3 can be exceeded by the floor area of structural facilities according to § 19 paragraph 4 sentence 1 of the Federal Land Utilization Ordinance (Note: date/reference) up to a floor space index of 0.6.
The floor area of ... m² stipulated on the parcel of land ..... can be exceeded by the floor area of structural facilities according to § 19 paragraph 4 sentence 1 of the Federal Land Utilization Ordinance (Note: date/reference) up to 120 percent."

The fact that the development plan in § 3 one allows exceeding the floor area ratio for terraces and access paths COULD mean that these are precisely not considered as "privileged areas" under the regulation of § 19 Baunutzungsverordnung, thus actually belonging to the main building, but an easing was intended for these. Therefore, the development plan is even less strict regarding areas than the Baunutzungsverordnung. Which would also be logical... rather smaller plots, dense development.

The fact that the development plan in § 3 one allows exceeding the floor area ratio for terraces and access paths COULD mean that these are precisely not considered "privileged areas" under the regulation of § 19 of the Land Use Ordinance, thus actually belonging to the main building, but an easing was intended for these.

Caution, you are mixing up things again: the access paths concern the pipe-head plots in WA1, the terraces are located in WA2 and WA4 (and here it is commendable that the development plan specifically addresses this, since views nationwide are not homogeneous as to whether terraces belong to main buildings or whether they must be directly connected to them for this assumption).

No, it was already clear to me that different plots of land were meant each time.

The point is: I think § 3 creates *facilitations* for the *main buildings* limited by the floor area ratio: for some regarding terraces and for some regarding access paths. Especially with the latter, this is very fair, as otherwise the owner would be disproportionately affected by the shape and location of their property. Provided my assumption is correct, that both elements, terraces and access paths, are counted as *main buildings* in that federal state, so they are not ancillary facilities and thus would not fall under the regulation of §19 (4). This one is additionally to be applied further with the values specified in the Land Use Ordinance. Since I am not allowed to post links. However, on the websites of the city of Hamburg as well as Munich and various law firms that offer courses there are guides for the creation of building plans. These can be found quickly by googling.

At the end of the day, only the municipality / building authority can give you a truly binding answer, and it’s best to have this clarified by an architect from the region, as they have more authority and also know better who can really give you a reliable answer (and they should receive one as well).

I had a similar problem and had to make several calls. Then came well-meaning but little reassuring responses like "I spoke with my colleague, it should be possible." After a brief relief, there was again a shock shortly afterwards when, at the second appointment with the architect, we were told that he rather thinks it is NOT permitted. We then had it clarified ONCE MORE through our architect, and it is indeed possible. Nevertheless, I am already looking forward to the waiting after submitting the building application.

So much for the quality of development plans. Unfortunately, it is very variable.

Oops, there seems to be quite a bit to correct here.

Plot = 554.6m²

The basis for the calculation is the registered area, which is recorded in the property cadastre and noted in the land register. This is always given in whole square meters, so this cannot be the registered area.
Otherwise, your calculation would be correct.
For the main buildings Floor Area Ratio I: 555m² * 0.3 = 166.5m²
For all structural facilities Floor Area Ratio II: 555m² * 0.3 * 1.5 = 249.75m²
If you fully utilize Floor Area Ratio I with house and terrace, you still have 83.25m² left for garages, parking spaces, driveways, ancillary facilities (garden house, greenhouse, ...)

Does § 19 para. 4 of the Land Use Ordinance have to be included in the development plan in order to apply it, or does it always apply?

The legal basis must be indicated somewhere on the documents, but not every paragraph. The Land Use Ordinance is federal law and therefore must always be applied regardless of the state building code. However, with §19 (4) sentence 3 it grants the municipality some scope for design.
Deviating provisions from sentence 2 may be made in the development plan.
The municipality has made use of this with §3 for your area WA1 under 3. To be specific: you do not need to include the access path to your house in Floor Area Ratio I.

In this respect, your idea (of cheerful summations) is indeed nonsense.

The original poster did not elaborate further on whether he actually wanted to apply a cheerful summation. I find your thought more questionable

Depending on the federal state, roof overhangs, bay windows, etc. can also be included in the Floor Area Ratio.

since we are dealing here with federal law and municipal statutes, and the state has no say in this.

You must also observe your Floor Space Index of 0.45.

Which is a very important note.

This development plan ... does not mention such a second Floor Area Ratio

That is exactly why the provisions of the Land Use Ordinance apply.

But shouldn't the development plan explicitly restrict the rules regarding garages contained in §19 (4) of the Land Use Ordinance in §3?

That is correct.

The municipality does not have to justify its urban planning intention.

Yes, it does. The demands on justifications have increased immensely in recent years.

It would not deviate from the maximum framework of the Land Use Ordinance

First, it does: the maximum framework would be 0.4 and second, it does not only apply the measure of

The point is: I think § 3 creates *reliefs* for the *main buildings* limited by the Floor Area Ratio: for some regarding terraces and for some regarding access paths. Especially for the latter this is very fair, otherwise the owner would be disproportionately affected by the shape and location of his plot. Provided my assumption is correct that both elements, terraces and access paths, are counted as part of the *main building* in that federal state, i.e. they are not ancillary facilities and thus would not fall under the regulation of §19 (4). This has to be further applied with the values as specified in the Land Use Ordinance.

Except for the restriction "federal state", I see it the same way. And there is not really consensus about the access paths, which still leaves room for interpretation.