I want to build in spring 2026

Hello everyone, I want to build a single-family house with a granny flat. A total of 250sqm living space. 150sqm will be the single-family house and 90sqm the granny flat. Of that, 10sqm goes to the heating room.

The plot price is 198€ per sqm.
For a 400sqm plot, that would be 79,200€.

Would 500,000€ be enough for the construction costs?

I want to do a lot of the interior finishing myself.

My maximum expectation for the total costs is 600,000€.

I would appreciate hearing about your experiences.

Before you get to the costs, it first needs to be clarified whether 400 sqm can even be developed with 2 residential units, whether the size of the property can then be that large (floor area ratio, plot ratio), and how many parking spaces you then also have to accommodate.

Otherwise, the rule of thumb is 3000 €/sqm, you state BW as the place of residence, I assume Baden-Württemberg, where the tendency is also towards 3500 €/sqm.

Do the interior finishing yourself ... what exactly? Wallpapering? Laying the floor? Usually saves less than you think because you still need the materials anyway.

I think, no, you won’t manage it with 600,000 €.

Would 500,000€ be enough for the construction costs?

Rule of thumb: 750k for the pure construction costs. In addition, there are incidental construction costs as well as costs for garages/parking spaces/terrace/outdoor facilities/driveway, etc. If you want to manage the entire house building project (with everything I listed) with 500k, you should rather assume that you have to build the house completely by yourself. And completely really means completely.

Hello people, I want to build a single-family house with a granny flat. A total of 250 sqm living space. 150 sqm will be the single-family house and 90 sqm the granny flat. Of that, 10 sqm go into the heating room. [...] I want to do a lot of the interior finishing myself.

400 sqm plot probably results in 160 sqm footprint = actually around 250 sqm living space as a detached villa two full floors (assuming a floor area ratio of 0.4). Interior finishing also costs money – however, as a self-builder, you can fool yourself if you don’t consider your hourly wage at zero without being retired. It is often forgotten that you cannot tile and day trade at the same time. 90 sqm granny flats are extremely weakly demanded; without a concrete long-term rental contract, I would not build them.

Doing interior finishing yourself ... what exactly? Wallpapering? Laying the floor? Usually saves less money than you think, since you still need the materials.

You won't save the project this way, that's true. But little savings? The painter charges easily 12,000 EUR for a single-family house. I paid around 1,500 EUR for good paint (Keim Innostar), drywall sander, and rollers. The tiler charged over 100 EUR/m², I could have gotten the materials for 40, 45 EUR/m². And the range for floors and doors is similar...

Doing something yourself because you inevitably have to save money also assumes that you are capable of doing what you are doing yourself. Most people can manage painting relatively well. Flooring, doors, and possibly other interior construction trades should not be underestimated in terms of craftsmanship. Of course, if you have years of time for building the house, you can grow into one area or another. Without further information from you, I consider the project – like my predecessors – rather too ambitious.