Construction costs: Single-family house in Baden-Württemberg 2019 (KFW 40 plus)

You should inform yourself again about the meaningfulness and also the economic efficiency of a KFW 40 (Plus) house. In my opinion, it may be ecologically sensible in the long term but not economical. So if you have the money, you can gladly invest it in this. If the budget is tight, you should reconsider.

For KFW 40 or Plus, a prefab house is not a bad idea. As a solid construction, this is harder to achieve. As an alternative offer, you can get a quote from Viebrockhaus. It is solid construction and KFW 40 Plus, and the provider is available almost everywhere.
I find 2500 EUR/sqm a good size. You should manage with that; it's not an excessive luxury for a 40 Plus house.

What I find problematic about your calculation is the basement apartment (does that add to the 150 sqm?). If the basement has living space quality and is then also supposed to be 40 Plus, why should it be cheaper than the other sqm? If you want the basement like that, also calculate with 2500 EUR/sqm. Pure utility basement maybe 70k.
20k for the garden is also tight on a slope. Usually, with a standard plot, it goes for paving the driveway, laying a terrace, and some greenery. Do you have to do a lot of shoring? Terrace the garden? Then certainly too little.
Garage or carport is missing. Kitchen and other furnishings are missing.

I'll give you a rough calculation (we are building ourselves on a slope with a basement, but not 40 plus) 150 sqm living space + 80 sqm granny flat in the basement: 230*2500 = 575,000 EUR as 40 plus Additional construction costs: 35,000 EUR Excavation: 35,000 EUR Carport: 20,000 EUR Outdoor facilities: 30,000 EUR Kitchen and some other furnishings: 25,000 EUR Final sum: 720,000 EUR Maybe it can be a little bit cheaper. But if you get total panic at that sum, think about where you can save. No KFW 40 plus (but standard KFW 55 or Energy Saving Ordinance) We are lucky to get rid of the excavation cheaply, maybe there is a possibility for you too. What is possible in EL? Oh, and one more bad news. In 2019, the start of construction probably won’t happen anymore if you are only now at this "rough stage."

Two years ago, the KFW conditions were so sh*** that I wouldn’t use them as a basis for my planning. Especially if you already have a plot of land that hopefully has some value, you will get good conditions anyway. A timber frame automatically becomes a KFW40 house with photovoltaics, but the designation is actually of little relevance. If solid construction is an option, I wouldn’t put much value on it, but rather consider the heating load for the energy assessment. Photovoltaics is always good.

Hello,

the costs have already been well broken down here. For the garden design and outdoor work, it naturally also depends a lot on how big the property is, how large the area to be paved is, etc. In general, construction costs have risen sharply in recent years and craftsmen are hard to find, also for outdoor facilities. The decision for a prefab house or solid construction is (also) a matter of taste. We built a prefab house because we were convinced by the short construction time, the fixed price and (in this case) the ecological construction method and are very satisfied with it. But it probably doesn't hurt to get other offers if you are not quite convinced yet.

Basement granny flat: 230*2500 = 575,000 EUR as 40 plus
Additional construction costs: 35,000 EUR
Excavation: 35,000 EUR
Carport: 20,000 EUR
Outdoor facilities: 30,000 EUR
Kitchen and some other furnishings: 25,000 EUR
Total sum: 720,000 EUR

Seriously, only for the house with a bit of garden, without land?
I didn't even know there are so many millionaires in Germany...

But now seriously, what kind of prices are these supposed to be?
600k just for a smaller house with a basement?
We’re building 200sqm with 100sqm waterproofed basement, 60 sqm of which is finished with a kitchen.
500k would have easily been enough for us if it weren’t for various extra wishes.

We’re building 30 km as the crow flies from the OP, regional price differences are irrelevant here. Sometimes I really wonder if everyone here is indulging in golden faucets or something else to get to such prices.

With additional costs, garage, hillside location, etc., this is unfortunately currently realistic. And they are not millionaires (at most in debt). If everything goes well, they will be in 30 years. With €2500 per m2 without additional costs, garage, land, outdoor facilities, etc., this is a good reference point in BW.