Interpretation of the 1957 development plan <-> possibilities for new construction

And if the legend says that red is a building line, then it is mandatory.

I cautiously ask from the side whether the ridge direction is also specified?

The existing building does not comply with the building line. The topic does not seem to be taken very seriously. I have sketched the existing building with roof overhang.



According to the OP, the ridge direction is specified but does not seem to be set in stone.

In my opinion, the parking space and garage can be a unit. The house behind the garage then on the setback line.

The plan says nothing about that.

We don’t know that. This again shows that plan fragments are not sufficient for forming an opinion. This applies especially to development plans that became legally binding before the introduction of the Federal Building Code, the Land Use Ordinance, and the Plan Symbols Ordinance.
You could get more well-founded answers and assessments if you showed the complete plan here and a current land registry excerpt. Then one could also see how strictly the building lines of the residential houses in the area of application were adhered to and whether the garages actually have to be within the building window, which your existing garage certainly does not.

Yes, there is only the graphic part of the development plan.

But hopefully a legend and maybe also a reference to the legal basis.

"optically from a recessed garage"

Show the full wording.

but why would it have to be 6m there?

It doesn’t have to be; the minimum distance depends on the building height. But information on your planning is still missing. Does your municipality have its own setback area statute?

… or could the shed be part of the house

Yes.

whether I am allowed to come within 3m of the boundary behind the garage

Yes, if it’s not too high.

It has to be within the building window.

Says who?

Then one could also see how strictly the building lines of the residential houses within the scope were adhered to and whether the garages actually have to be within the building window, which your existing garage does not do.

I took the trouble to sketch the existing situation into the plan (post #13); the garage is exactly within the building window of the development plan. The house, however, is 4 meters away from the building line, if it is one.

I took the trouble to sketch the inventory into the plan (post #13)

Yes, I saw that.

the garage is exactly within the building window of the development plan. However, the house is 4 m away from the building line

However, that does not match the information from the OP. According to that, the house stands exactly on the building line and also on the northern building boundary. The garage would then partially stand outside the building window, which can be permitted according to the building use ordinance, except that it did not exist in 1957. Therefore, I would like to have a generous excerpt from the cadastral map. Then one could estimate how many ancillary structures stand outside the building window and how many neighbors deviate from the building line, which would allow conclusions about the exemption possibilities.

The OP wants to understand how to interpret the development plan, and only someone who knows the entire plan and the entire reality can help with that. A pixelated aerial photo of the building plot without reference to boundaries and with hardly recognizable neighboring buildings is not sufficient for that.

I once sketched the existing structure with roof overhang.

I took the trouble to sketch the existing structure into the plan (post #13),

However, that does not match the information from the OP.

I also see no identity there. I have not even overlaid the plans yet, but the front distances approximately fit. At your side, something at the back is apparently shifted or the building structure runs differently.

I also do not see any identity there. I have not even overlaid the plans yet, but roughly the front distances fit. At your place, something shifted at the back or the building mass runs differently.

But I do, then traced it as well as possible. The blue line.

is right though. A section from the cadastral map is helpful (more precise). It is easy to copy out from the geoportal.