ᐅ Single-family house with a separate apartment, double garage, and basement – construction costs of $1,000,000?

Dear Forum,

My husband and I are planning the construction project mentioned above. We have now received some initially shocking price estimates. Here are a few key details:

- Plot of land owned in North Rhine-Westphalia (rural area, not Rhineland)
- Single-family house with approximately 220 sqm (2,368 sq ft) of living space, including a 60 sqm (645 sq ft) granny flat, plus a waterproof concrete basement (WU concrete) of about 140 sqm (1,507 sq ft) – total: around 360 sqm (3,875 sq ft) of living / usable space
- Solid construction, brick veneer, 1.5 storeys, gable roof, pent roof dormer
- Plain architecture (no extravagant large window fronts, no floating stairs, no large spa or wellness areas; only luxury: an "external staircase" from the basement to the garage)
- Double garage (not a prefabricated garage)

Originally, we roughly estimated about €2,300 per sqm (square meter) average construction cost for the main house, plus €700 per sqm for the basement, plus €50,000 for the double garage. Based on these assumptions and a floor plan idea, we asked one national and one regional general contractor for rough turnkey construction quotes including interior finishing – the national contractor estimated between €800,000 and €850,000, the regional provider even nearly €1,000,000. In both cases, the basement was priced between €150,000 and €200,000, with the indication that a partial basement should allow for significant savings (how significant??).

Questions:
1. Is the estimated price for such a basement typical? We had actually planned for about €100,000 for the basement, i.e., around €700 per sqm.
2. Is a partial basement structurally so complex that overall it does not really pay off compared to a full basement? Or, given the size of the ground floor, is it financially reasonable to build a partial basement?
3. Is a WU concrete basement as a partial basement advisable regarding long-term waterproofing? Or put differently: Can one reasonably rely on a WU basement not needing to be excavated and waterproofed again in the future, which would surely be a nightmare for a partial basement?
4. Is a surcharge of around €100,000 for the insulated brick veneer facade normal for a house length of about 15 m (49 ft) and gable ends approximately 10 m (33 ft) wide? We have roughly around 150 sqm (1,615 sq ft) of facade area (excluding window areas).
5. What should we do?! 🙂
a) Reduce the size of the house? (This only makes sense if the price decreases roughly proportionally, which we did not expect – actually, we had not thought that a house with 220 sqm (2,368 sq ft) living space could cost almost twice as much as one with 150 sqm (1,615 sq ft).)
b) Skip the basement (difficult, since there is a lot of equipment and because of the layout with the granny flat on the ground floor, the floor plan is not very flexible)?
c) Instead of the house, cellar the garage? (Is it possible to excavate almost up to the property boundary? The garage has so far been planned as a boundary wall construction.)
d) Request quotes from additional construction companies?

We are sincerely grateful for any good advice. Until now, we had not expected to have so underestimated our - to our feeling generous - planning.

Why should the basement be significantly cheaper than the above-ground living space? It also needs to be within the thermal envelope, meaning it has to be insulated and connected to the heating system (underfloor heating), and the ceiling height is roughly the same as standard living rooms. A slightly cheaper choice of tiles, doors, etc., does not account for savings of 1600 EUR per square meter. I would consider 800-850k as realistic, excluding additional construction costs such as basement excavation, landscaping, and interior fittings. The basement is just very expensive to build to a high-quality standard and then used only as storage and a workshop. I think 150-200k is realistic for the basement. Adding a basement under the garage, approximately 60 sqm (645 sq ft), probably costs around 80-100k, at least with heating, standard ceiling height, and other requirements for living spaces.

Crossy schrieb:

Why should the basement be significantly cheaper than the above-ground living space? It still needs to be within the thermal envelope, so it must be insulated, connected to the heating system (underfloor heating), and have a ceiling height similar to standard living areas. A slightly cheaper choice of tiles, doors, etc., does not justify a saving of 1600 EUR per sqm (approximately 150 USD per sqft). I would consider 800-850k as realistic. This excludes additional construction costs, including basement excavation, landscaping, and furnishing. The basement is quite expensive if built to a high standard and then used only for storage and as a workshop. I think 150-200k is realistic for the basement. Adding a basement under a 60 sqm (645 sqft) garage would probably cost around 80-100k, at least if it includes heating, standard ceiling height, and other requirements for living spaces.

We researched online and found corresponding prices per square meter. Since the wall construction would be simpler, with only a few small basement windows, more basic interior finishes, no complex technical installations (no concealed wiring, etc.), and no bathrooms to raise the average cost per square meter, we assumed the estimate might roughly be correct. But thank you for the expert assessment!

Welcome to the world of construction. After all, you want to build a house with approximately 1300 m³ (46,000 ft³) and have a huge basement. A budget of at least €800,000 is quite realistic. It is probably closer to €1,000,000 including all additional costs (ancillary construction costs, fees, financing fees, kitchen, etc.), as one of the providers suggested.

What do you need the granny flat for? I guess that painting it will save the most.

The separate apartment is the only part that will remain unchanged. A dependent family member lives there. Therefore, it is on the ground floor and accessible for people with disabilities.