Questions about basement construction in relation to KfW 40 Plus

Good morning everyone on this rainy Sunday,

after we requested offers from several providers for a kfw 40 Plus house, we are now thinking about the basement. At the beginning, it was clear that we wanted a basement with living space. Now two providers have informed us that we must expect around 100-120 T € for a kfw 40 Plus house with a living basement (this seems very high to me, but they argue with the insulation and underfloor heating; the earthworks are included in this price, the basement has an area of 10x10). Due to the high price, we are now reconsidering whether it really has to be a kfw 40 Plus house or if a kfw 55 house would also do.

Since we unfortunately have few opportunities to exchange information about costs and experiences with other builders, I wanted to ask you:

1) Is this price realistic for a living basement?
2) Are there approximate benchmarks for how much cheaper a living basement becomes if you do not build as a kfw 40 Plus house?

Many thanks in advance and have a nice Sunday to you all

The price is about right. That is 100 sqm of floor space "downwards" in living space quality, i.e. higher ceilings than normal utility cellars, complete interior finishing, second escape route, etc. The extra cost from KFW 55 to KFW 40 should be marginal. That means 4-6 cm more insulation in all directions and that's it. You might save around 3-5T€ on that.

Hello Alex85,

thank you very much for your quick response. It is already good if someone considers the price to be realistic. On the internet, you always read "we plan 40-60K for the basement," and for us, it is supposed to be twice as much.

Are there any possibilities or does it make sense to prepare the basement as a living basement and then tackle the entire interior construction later? At the beginning, I want to keep the costs within limits, and we are already near the pain threshold when including the 10% for all contingencies.

Best regards

The price information applies rather to utility basements. Residential basements have higher ceilings, i.e. they are deeper in the ground. Earthworks are not cheap. However, the term Wohnkeller is also used carelessly. Putting a carpet in a utility basement does not yet make it a residential basement. Ultimately, residential basements cost the same as above-ground living space plus underground construction. Therefore, one should also question why it necessarily has to be a residential basement.

Preparation ... depends on what condition you expect at the beginning and how it is to be executed. If everything is to be concrete, you will have to plan the electrical system directly if later everything is not to be surface-mounted. Heating must be installed from the outset, as well as the screed (assuming underfloor heating) ... I don’t think you will save much on that. Maybe painting and flooring (although at least the connection room would have to be done here).

We have a white tank as a prefabricated basement at 10.5 x 10.5 m. However, here we have a raw construction height of 2.385. In the basement, we do not have underfloor heating, only radiators. For us, that is enough. For this, we pay €70,000. But we build according to [Energieeinsparverordnung 70], because we believe that anything higher is not worth it.

Thank you for your answers - I’m slowly also becoming unsure to what extent a kfw 40 Plus house is worth it. We were told that starting from 2021 a KfW 40 Plus house will be mandatory and a potential resale value without this standard will be significantly reduced. Can one roughly estimate the additional costs a kfw 40 Plus house entails compared to a kfw 70/55 house?

Best regards