New single-family house construction in 2025 possible on a low budget?

Additional construction costs (e.g. house connections, soil surveyor, construction electricity, etc.) €20,000 should be enough?

No, unfortunately not enough. You can read about the costs in the subforum Construction Costs.

Renting later for about €1,000 rent is possible, then the repayment continues. A private loan at 1% is therefore flexibly manageable.

I would say: the bank says no. Rents are often unstable, fluctuating, and unreliable. I am currently experiencing this multiple times in my environment. Renting is always only and not gladly seen as a Plan B. If you sell your apartment and increase your equity with it, the bank says yes to financing.

Thank you very much for the numerous responses. The apartment has an emotional value, it is a family house where I grew up. The house has three units, is self-managed because it is all family. The heating system was replaced in 2022 with pellets and solar, new windows in 2019, new electrical wiring and completely renovated inside. There is an air conditioning system, wall box, two parking spaces and a garden area. I acquired it normally, not as a gift. Maintenance is carried out by myself. We have just viewed the existing property. If we are able to obtain financing in the current situation (parental leave) we will make an offer. The plan would be to implement energy measures over the years and first only make the interior nice and move into the ground floor apartment and rent out the attic apartment until the need for space arises.

The apartment has an emotional value, it is a family house where I grew up. The house has three units, is self-managed because it is all family.

Then keep it and stay living in it. That would be the consequence you describe with emotionality, before someone else wears it out. As harsh as it may sound, you have to be able to afford emotionality.

I don't see financing the €473,000 as feasible for us.

It is more like €500,000+, since the additional construction costs were calculated too low and also (the unmentioned) buffer is usually used up. Were the floor coverings included in the calculation, which Town & Country does not carry out?

Possibly, the house costs can be reduced to €300,000 by using own labor.

That won't work. Town & Country offers you turnkey house construction as a general contractor, works with subcontractors who can hardly let you cooperate for insurance reasons alone and indeed also have their own employees…

I have a craft background, can do many things myself (install windows, erect roof, cover and insulate it, drywall, lay floors, painting),

You cannot cover the missing €200,000 with auxiliary work. Your financing will not be approved with such a calculation gap.

Today we are looking at a property for €450k with 600m² of land and a second residential unit but unrenovated from 1975. Some renovation work can be postponed into the future, with correspondingly available liquidity.

Phew, but you have to do quite a lot initially. Something is missing in living costs. Is it the leisure point? Well, you compensate for these expenses with the side job.

I would really be interested now, the original poster probably too.
Let's take the Bodensee 129, which costs 270,000 EUR in a mid-priced region like Hannover, turnkey.
That makes 2,100 EUR/m². What is still missing to get to 3,000 EUR/m²? Or even beyond that.

Please explain.

I built with Town & Country and I would also be interested in what is supposedly even more expensive.

For me, 10 years ago, it was 12,000€ for the lines like gas, water, telecom, sewage
Then also
3,000€ for additional foundation
2,000€ for removal of excavated earth and refilling (could be stored on the property, no basement)
1,000€ construction water and construction electricity
3,000€ surveying costs
Notary and real estate transfer tax as well.

I had a bit more tiles laid on the ground floor, an entrance area is definitely nicer if it’s tiled. But theoretically you can manage all this yourself with floors and painting work. Of course that costs a bit of money and especially time, but definitely not huge sums.
Material including tools was around 5,000€. You just shouldn’t pay pharmacist prices.
My Nolte kitchen was 5,400€.

Garden design, house edging and paving the yard was another solid 20k.

If I estimate 50% cost increases, I’m at 46k + 50% = 69k

and I would also be interested to know what is supposedly so much more expensive then.

Because the mentioned Bodensee 129 is not the LandHaus 142 and the price is also different.

Town & Country Landhaus 142 from 350,000 at our location, I am calculating with 400,000 due to price increases and minimal possible customization

I assume 50% cost increases

So you built with Town & Country 10 years ago. Then be happy about your construction prices from 10 years ago.
The popular Flair 110 has become a lean 110-120% more expensive in the last 10 years depending on the region. That says a lot about the development of construction prices even with a low-cost builder.

But theoretically, you can also handle everything yourself

But we are always talking about the prices of a finished house. Own efforts make it cheaper, that is correct. However, if someone asks about construction prices, they are given the average prices of a finished house into which only the furniture still needs to be moved.