House costs, first reality check

Good morning,
that is of course an important point. I had not written anything about it yet.
The basement of the old building is of course not deep enough. I estimate that you have to go 1m deeper.
But in terms of area, it fits quite well. The building lines and building boundaries specify quite a bit.
I would say the old building is 9x9m + extension.
The new building should then be 8x10 or 8x11m.
Garage old building at the same place as garage new building.
The extension of the old building 5x9m would then roughly be the area where the terrace is to be located.
The demolition contractor said that the debris could be crushed and used as load-bearing gravel replacement.
We know that the soil is very clayey.
The developer has already built 4 city villas in the immediate neighborhood. Therefore, he is already familiar with the conditions.

May I ask a parallel question in this thread? (If not, feel free to start a new thread)

In view of the construction costs, the option to sell the plot is also still open for us. (Since it is quite large)
We already had an appraiser (certified for the tax office) out there.
He determined a value of 1.1 M based on the standard land value + WGFZ - demolition costs.
(I have a follow-up question regarding the WGFZ)

Are there any experiences from the community on how well this determined value can ultimately be realized?
I can only look for comparable offers on the portals myself. But first of all, I do not know at what price they were then sold. Or if the offers have been online for a while, the requested price could be too high. (You just see what is possible). Or if the offers are no longer online, you don’t know if they were actually sold or if there was simply a pause.

I already consider the 1 million for the 170 sqm including additional costs etc. to be rather high-priced. If you put in some effort and don't always go for the top shelf, in my opinion you might be able to save 10-20% there. Is there a soil report? What does it say about the ground or the sealing of the basement?

The value for the tax office can sometimes have very little to do with the real value, although it is of course an initial guideline. For that amount, I would maybe additionally have an expert appraisal done or ask a few realtors for their opinion for free. What does the standard land value say? It probably won't be much below that.

Hello,
we do (still) not have a soil report. We only refer to the recently built urban villas in the direct neighborhood, who mentioned the clayey soil to us. They had to (expensively) replace the soil back then to make it load-bearing.
For us, this partly does not apply because the existing basement was already level with the ground.
(In the case of the urban villas, the floor areas did not fit the old structure. 4 houses on 2.5 plots)

The real estate appraiser used the (current) standard land value and converted it to a possible development.
Then deducted the demolition costs.
I was able to follow the calculation method. However, this floor space ratio (WGFZ) seems a bit suspicious to me.
It is probably difficult to determine a market value for a demolition object.
We have already used first free real estate agent inquiry tools. These, of course, are partly quite rough or only give a range. In the end, it is difficult when the result says 680-1700.

Seems like a good area, just ask a reputable real estate agent, they have experience and in my opinion will gladly give you a number. Of course, they hope for a deal. The floor area ratio is already very relevant for a plot, because a huge plot is of little use to me if I am only allowed to build a small house and vice versa.

Definitely have a soil survey done (anyway), because with clayey soil water can possibly be a problem - do you have to build a waterproof concrete shell or is drainage enough? Waterproof concrete shell for a large basement easily costs 30k+ extra.

I consider the 1 million for the 170 sqm including additional costs etc. to be rather on the higher priced side.

It’s actually only 900k (the rest is buffer/outdoor facilities) for 170 sqm including full basement, double garage, existing building, possibly difficult foundation including demolition etc.
That’s fine.