Cost of Floor Slab/Basement and Interior Finishing - Fact Check

We are currently feeling our way into building a house (plan: 120-130 sqm living space, 2 floors, approx. 70-80 sqm footprint) and had a first appointment yesterday with a Schwörerhaus salesperson. As these conversations usually go, we discussed all sorts of topics, our needs, budget, etc. It was okay overall, although the price (for a prefabricated house) did put me off a bit. The consultant said that currently it would be around 3,300 EUR/sqm. The 3,000 mark was already known to me, but I thought that it would be somewhat lower for prefabricated houses. Is Schwörerhaus one of the more expensive providers?

Be that as it may. There were some statements from the salesperson that seemed a bit odd to me as an "informed" layperson:

[*]Basement vs. slab foundation:
It was more or less clear to us in advance that we would not be able to afford a basement. I also communicated this during the conversation. Salesperson’s statement: depending on the soil, the slab foundation could be just as expensive or only slightly cheaper than a basement. If things go badly, the pit for the slab would have to be dug just as deep (down to a load-bearing layer) and filled in, meaning costs for the slab foundation could quickly be around 50k EUR. The basement at Schwörerhaus would probably be around 55k EUR. This way, you could save above-ground space, which might be a zero-sum game. As a layperson, I could not oppose this. For the slab foundation, I had assumed costs of about 20k EUR; after extensive research, I had estimated the basement at around 100k EUR. The Schwörerhaus basement seems very cheap to me.

There is no soil report yet for the plot, but the area was developed by the city and a test drilling was done near the plot at the time; see result below. Even though this cannot replace a soil report, maybe some initial conclusions can be drawn from it.

[*]Savings potential for shell construction/interior finishing:
We would like to do part of the work ourselves (especially interior finishing). Here too, the salesperson said that this is of course possible, but one should not have too high expectations, since the labor cost share to be saved is "only" 50%. He then showed me the costs for a similarly sized house (walls/ceilings 17k EUR, floors 18k EUR, sanitary 7k EUR). Savings potential at 50% thus under 20k EUR, but possibly more time and additional costs (rent, equipment, etc.). Since Schwörerhaus offers a wide selection of high-quality materials, additional costs when upgrading should also be limited. I (perhaps somewhat naively) assumed that you would come out cheaper with shell construction houses; apparently, this is not the case?

Just wanted to post this here and ask for your opinion. We are still at the beginning of our journey and, of course, have further appointments with house providers planned.

Many thanks in advance!

Well, I'll put it this way: The prices quoted to you sound pretty realistic for Schwörerhaus. Yes, Schwörerhaus is rather one of the more expensive prefabricated house providers, but it is also known for building quite qualitatively. It was almost to be expected that they wouldn't go with a 2,500 €/m² standard price. Whether it's worth it to you, of course, is another question.

Regarding the topic of ground slab vs. basement: Your assessment is not entirely wrong; normally, the basement is significantly more expensive than a ground slab. But: The seller's note about difficult ground conditions is not entirely unfounded. If you look at the soil profile in your picture, you can see almost continuous clay and silty layers down to about 5 m depth. Depending on load-bearing capacity and water conditions, this can indeed lead to increased effort. So if you need to go down to the load-bearing layer and then fill up – yes, a ground slab can become very expensive. In that case, a basement can suddenly become economically more interesting, especially considering that it can save living space.

But without a proper soil survey, all of this remains speculation. If you are seriously considering the plot: get your own survey soon. It costs a few hundred euros, but it can save you five-figure amounts or nasty surprises.

Regarding the shell construction: Yes, doing it yourself basically saves money, but only if you have time, skills, and the will to put in the effort. A 50% saving on labor costs is a realistically set value; if you do a complete trade yourself, you save the installation. But you still have to buy the materials, maybe even more expensive at retail. Rental equipment, longer construction time (with rent), possibly mistakes and rework – that adds up. Many builders tend to overestimate themselves, especially with their first house build. If it suits you: go for it. But better to be honest with yourself.

In short: Schwörerhaus is not cheap, but solid. I wouldn't dismiss the seller's statements as nonsense, but of course, they are also sales-oriented. Get other offers, get a soil survey, and stay alert with the contracts. Then you can also be happy with a prefabricated house.

The building ground is really interesting. Considering that you have to dispose of 5m x 14m x 14m of soil and then refill everything, it certainly won't be cheap. I estimate the costs for excavation, mineral concrete, and foundation slab at 90K. Basement would cost an additional 60K.

To get 130 sqm of living space out of 80 sqm of floor area, you must be allowed to build a "city villa". A single core drilling test says too little. The more homogeneous their results are in comparison, the fewer are needed. On the plot, at least two should be done, diagonally at the corners of the building window. A basement is not solely your decision; the plot plays a significant role. Also compare my 11ant basement rule, which can be found externally with the search phrase "Mit oder ohne Keller: eine Regel als Entscheidungswerkzeug" (it deals less with the aspect of soil replacement mentioned here and more with determining the breakeven considering the phenomenon of when the costs of avoiding a basement can exceed those of building one). A shell house (to contribute own work) only noticeably saves money if you can really contribute significantly (without being slow), and a shell house (dreaming of being a successful bargain hunter when finding craftsmen) even less. Forget about that if you would need it for the calculation to work at all. Time is also money – many willing to do their own work underestimate the decline in their performance curve and then have to remain renters longer (while they are already paying off their own home!), because as laborers they simply cannot achieve adequate professional productivity.

"Finished" and "solid" houses, by the way, are equipped identically and also priced the same. First plan phases 1 and 2 with an architect, and then take a decisive step during the resting phase (see "A house-building roadmap, also for you: the HOAI phase model!"), after whose result you either continue planning individually in wood or stone or have a catalog house adapted.

So I'll put it this way:

I can agree with that.
Furthermore, Schwörerhaus is not among the home builders who generally offer upgrade levels. At least I wouldn't know of any.
If you have to watch every cent and possibly want to do some things in EL yourself, you are better off with another company. Possibly also with solid construction; timber frame construction is not cheaper.

Hi,

so what the Schwörerhaus guy told you is not completely off, but already a bit of "sales mode". The 3,300 €/m² are really nothing unusual for Schwörerhaus, they are rather in the upper mid-range, but relatively well planned and solid. It rarely gets cheap there. That a foundation slab sometimes moves towards 50k with difficult ground conditions can happen if, for example, you are sitting on non-load-bearing soil and have to fill a lot. But without a soil survey, it's just guesswork. Get that thing before you plan further, otherwise it can blow up financially in your face.

Regarding the basement: 55k for a basement sounds really cheap for Schwörerhaus. Realistically you are rather somewhere between 80k and 100k, depending on equipment. If you are thinking about accommodating technology and storage space in the basement and save above-ground space, it can sometimes be economical. But you have to calculate that carefully.

On the subject of shell construction and own work: You only save something if you really have time, know-how, and nerves. And even then only if you really get stuck in, like doing screed, electrical work, painting, etc. yourself. Just painting a wall won’t get you anywhere. You have to pay for materials anyway, often at a higher price, and you still need craftsmen for tricky things.

If you have to watch the money and are willing to help out yourself, also take a look at solid construction with an architect or cheaper providers with a real shell construction option. And first clarify the thing with the ground, everything else is otherwise crystal ball.

Best regards