Financing plan for new construction on existing property

€230,000 just for the land is already outrageous.

In Kaarst 310 TEUR for 125 sqm including additional construction costs.

180 sqm for 310 TEUR + additional construction costs... Never!

Our plot has a BRW of 217 TEUR. Not unrealistic and Neuss is still between us and Düsseldorf.

Financing is adequate so far

In principle, this is feasible and probably a better situation than many others.

You should calculate your affordability based on only one income as a precaution.
With that, it should be possible to pay everything off before retirement.

If, as previously requested, you can break down the "buffer" into individual items, then in my opinion it is no longer a buffer. What I mean by this is that you should not have taken this buffer into account with specific measures in any way, so that it is really available for absolutely unknown costs (and those almost always come). Otherwise, you would have to increase your buffer if you already have realistic/probable scenarios for using up the buffer.

Also consider that a house causes higher additional costs plus taxes and insurance than an apartment.

Without questioning the framework conditions of the house and land and their sense or nonsense, I would continue to pursue the project based on the given information.

With the bank, possibilities for installment changes and special repayments should be agreed upon (without changing the interest rate), so that you can react, for example, to job loss. In addition, I would recommend a very long fixed interest period (at least 20 years). Higher interest, but then you won’t sleep so restlessly in years 5-10.

If you, as previously requested, can break down the "buffer" into individual items, then in my opinion it is no longer a buffer.

That is correct, but in the original post it says:

House: €310,000
Land: €230,000
Additional costs: €60,000
Special requests/Buffer: €40,000

In my opinion, the additional costs are just enough for the essentials (taxes, fees, and typical incidental building costs). Then we have the house and land and only one further item "Special requests/Buffer." In special requests must(?) now include
- Sample reserves, if the house is not yet fully planned (which is to be assumed)
- Construction period interest, commitment interest
- Outdoor facilities
- Expenses (construction supervision, topping-out ceremony, moving van, ...)
- Furniture (kitchen, lights, mirrors, wardrobe, ...)
- ...???
There remains a remainder (greater than zero?) for the actual buffer.

Also from my point of view, the financing fits due to the generous income and very ample equity capital. Only whether all the key data of the project are already so clear, I would quietly doubt, although I generally like to accept the information from the thread starters without criticism (see also #4, #5 and #8) ;-).

There remains a remainder (greater than zero?) for the actual buffer.

That is exactly what I meant by that, towards you it was intended as an agreement on my part.

We have €65,000 in additional costs including flat rates for sewer, kitchen, driveway, garden, carport. For us, the usual 6.5% property transfer tax and notary fees were added to the land (which was also fine), as well as estimated development and final road construction contributions of €30-40/m² for previously undeveloped land. Then we also have a buffer of €20,000.

Interest etc. is included in our annuity, so I do not take out a separate loan for this, but include it directly in the financing and repayment plan.