New construction financing - selling old house - experiences?

Actually, no.
1. Selling the house and staying as a "tenant" in the house until moving out
- costs rent
- delays can be annoying if the new owner wants to move in and you can’t move into the new house yet
- costs money
- no certainty about the sale price you will get
2. Bridge financing
- costs money
- delays only cost money, no stress
- no certainty about the future sale price you will get for the house
3. Use of equity
- costs you "only" equity
- lost income from investments
- possibly paying capital gains tax
- no certainty about the future sale price you will get for the house

You can and must weigh for yourself what suits you personally best. All options cost money, although it is not precisely predictable in advance what amounts.
If you assume that you can move in quickly, I would choose option 1. If it takes longer, option 2.

Thanks for summarizing, this is probably what it looks like in the end.

Regarding 1. It is naturally somewhat a matter of negotiation and how much the buyer "wants" the house. I know many examples here from the immediate area where the listing prices were exceeded again through bidding processes, even now in the supposed high-interest phase, which actually isn’t, the money is still very cheap, but construction costs have also skyrocketed.

It is also fundamentally worth mentioning that in this option all risks of the existing house are eliminated. High repair costs that might arise unexpectedly, for example, transfer to the buyer from the sale onward, and so on.

Regarding 2. If I can’t manage 1 in the shortest time, I have bridge financing offers at hand and will probably use them; the same applies if the usage compensation is "too high."

Regarding 3. This is ultimately the absolutely least profitable option. I also have to consider what the stocks lose in the long run, and we’re also talking about the lost compound interest, etc. That is naturally amplified further. It would be an emergency solution, for example, if I didn’t have bridge financing.

You are right; ultimately, it’s more about the feel-good effect—what feels the most comfortable.

There is already a kind of "sporting ambition" to get the best out of it. I can’t get that out of my entrepreneurial soul.

If you have been active in forums for a long time, there are always at least two sides to a medal and possibly a lot of solidarity and fairness. This also applies to selling and buying real estate in the private sector. Everyone should see their win situation in this. Too much information is often not good in a forum if it is not related to the topic.

the bank knows, existing property, other properties, a large motorhome, 6 months old, list price 350,000€ and a stock portfolio well above the intended amount.

Why the motorhome is „listed“ here, I don’t know. Such a thing either breeds envy .. yes .. or people pick it up ..

Sometimes people from outside simply have good ideas

.. and give the advice to live in it. I actually found and still find the idea quite nice and not far-fetched. It’s an experience worth trying, which theoretically you could also turn into money.

If you have been active in forums for a long time, then there are always at least two sides to a coin and possibly a lot of solidarity and fairness.
This also applies to the sale and purchase of real estate in the private sector. Everyone should see their win situation.
Too much information is often not good in a forum if it does not belong to the topic.

I’m thinking about it. Your objection is completely okay.

The too much information probably refers to the motorhome.
I only mentioned it because I mistakenly assumed it could be provided as additional security to possibly "improve" the conditions – I was not aware that no bank does that.

My main bank (commercial bank) definitely considered it an "idea," and I wouldn’t really know why they shouldn’t do it. They can include it as further security worth an additional €100,000, which they always receive. But this should not be any further topic here.

.. and advises to live in it. I actually found and still find the idea quite nice and not unreasonable. It’s an experience worth trying, which theoretically could also be turned into money.

For various reasons, for example, that is not possible, but I don’t want to discuss them here. Just this much: other persons belong to the household who, for example, depend on a wheelchair, so where would they stay during that time?

Unfortunately, I cannot offer you an attractive solution in your case either..

But I would like to explain to others why this situation is a good reason not to repay a home loan "at all costs"... instead, to save the available money!

My approach was always.. repay as little as possible at a low interest rate! Of course, we had set a reasonable repayment amount for ourselves, but instead of giving it to the bank, we saved/invested it. We did this for about 17 years. This put us in the comfortable position of having enough equity available for our new build, without having to sell the old house in advance for financing. An additional loan of about one third of the construction sum rounded out the new build financing and made it comfortably affordable. Since the loan for the old house was about to expire before the sale, I extended it for another year, and we gained time without pressure to sell. We then paid off the remaining loan amount from the sale proceeds.

I unfortunately cannot offer you an attractive solution in your case either..

However, I want to explain to others why this situation is a good reason not to “pay off at all costs” when it comes to a mortgage... instead, to save the available money!

My approach has always been... with a low interest rate, repay as little as possible! Of course, we set a reasonable repayment amount for ourselves, but instead of giving this to the bank, we saved/invested it. We did this for about 17 years. This put us in the comfortable situation of having enough equity available for our new build without having to sell the old house in advance for financing. An additional loan of about one third of the construction sum made the new build financing complete and comfortably affordable. Since the loan for the old house was just expiring before the sale, I extended it by another year and we gained time without pressure to sell. From the sale proceeds, we then paid off the remaining loan balance.

The scenario described is only advantageous under the condition that the interest rate for the follow-up financing also remains at a low level. If the initial loan was serviced with only minimal repayments over the term and, in the course of the follow-up financing, an interest rate of, for example, 3.7% becomes necessary, the low repayment portion due to the previously low interest rate (e.g., 1%) can have a negative effect. In this case, the resulting financial burdens could increase significantly, thereby negating the originally calculated advantage.

If the interest rate for the follow-up financing has risen sharply, you can use your saved equity and reduce the loan amount. This also works well without building anew. At least you have kept the option in case the interest rates stay at a low level. That was the case for us and it significantly simplified the process of new construction/selling the old house.