Assessing the affordability of home construction and criticism

You simply first buy a used kitchen for €1000, and gradually do the exterior work yourself. I would never let a house purchase fail over such things. And, for example, there should be no additional land register entry, since he already owns the plot. I would just inquire directly with the usual brokers whether I could get the financing. If you agree that it might be tight, and are also willing to take a second job or give up vacations etc. if something unexpected comes up, I think it can work.

Not quite right. The bank still owns the plot, as it is currently being paid off. And if another ranking is entered in the land register, who do you think will pay that? Certainly €1000+. And then the biggest problem, the reserves. What if prepayment penalties become due? He can barely save €1000 per month. Everything is more than just tight.

How is that supposed to work? Doesn't the bank end up in second lien? You haven't answered the question about fixed interest period and variable interest.

Who pays the 20k€ for the kitchen and who covers the ancillary financing costs like land registry entry, etc?

I wouldn't rely on 1.1%. I rather see 1.4-1.6% for you.

Very many uncertain things. I wouldn't do it.

fixed interest period 10-15 years
The property is an annuity loan
Financing costs like land registry entry have already been paid because the property already belongs to me.

Not entirely correct. The property still has the bank because it is currently being paid off. And if another lien is registered in the land register, who do you think will pay for that? Certainly €1,000+. And then the biggest problem, the reserves. What if prepayment penalties become due? He can hardly save €1,000 per month. Everything is more than just tight.

Okay. You are right, he has to pay for the entry of the land charge.
It would be best if he financed the house with the same bank as the property.
He has a savings rate of €1,000 plus €700 for vacation and the like, which he could first save as well. From that, such things can be paid.

It is certainly tight, but in my view doable with over €4,000 together.

Not quite right. The property still has the bank, as it is currently being paid off. And if another lien is registered in the land register, who do you think will pay for that? It’s certainly €1,000+. And then the biggest problem, the reserves. What if prepayment penalties become due? He can just about save €1,000 per month. Everything is more than just tight.

Just about saving €1,000. You really have to wonder who can still afford a house if that’s not enough. And that despite €1,200 expenses/month for apartment and land.

Aside from that, there is still €5k/net every 6 months as a bonus.

While I understand what you are saying, I think we are in a slightly different situation here. It is foreseeable after all. It is basically the decision now or in 3 years, but what fundamentally changes?

In three years you can probably afford it, today rather not.. You save 1000€ and have a warm rent of 500€ – and in addition to the land loan you want to amortize 700€ plus another 1200€ for the house. On top of that come the ancillary costs. So 1200€ second loan and 300 ancillary costs – 1500€. It just barely adds up.

And since you can only negotiate a house loan with the bank from the land loan (second rank), in my opinion you will not get top interest rates. Your financing costs will increase. Have you talked to the bank? Financing advisor sounds very generic. Especially the idea that the bank recognizes the land loan in first rank completely as equity if they also broker the second rank for you.

You then spend 700€ + 1200€ + 300€ = 2200€ on housing. That is quite a lot with >50% of your household income, in my opinion too much. You are in the probationary period (loan??) and here you just have to wait until your girlfriend is finished. The marriage is not yet concluded, meaning no advantage can be taken from splitting here.

The land is already included as paid off in the calculation (several advisors have said), then equity through own contribution plus the 15k that will then be there.
We ended up at 80-85% financing.

I don't know which calculation wizards are at work here, but you have paid off €25,000 for the land and €11,000 in cash.
With a project volume of €475,000, that is about 7% equity. And honestly, you certainly cannot include the €11,000 cash in the financing, but have to keep it as a buffer.

The land is an annuity loan

Then the bank is already in the first rank. Either you pay the prepayment penalty (how high is it for you?) or you are bound to exactly that bank, because no other bank can go into the second rank. So you are forced to refinance your €50k remaining debt on the land. Or where should the money come from? Have you already spoken with the bank that holds the loan? Or only with independent advisors?