ᐅ New construction of a solid masonry house on an existing basement

Hello dear forum,

I have a plot in the southwest of Berlin with a prefabricated house by Streif Haus, built in 1970, including a fully basement. My goal is to remove the house, keep the basement, and build two full stories on top. All building specifications, plans, and layouts are still available.

After my first inquiries with construction companies, I was immediately told that they generally do not undertake such projects and that only "desperate companies, probably urgently needing contracts" would take on such a project. The owner of one company himself said he does not know anyone in the Berlin area who builds on existing basements because it is an "unpredictable risk regarding warranties and guarantees," and I should let go of the idea. He would, however, be happy to build a new basement for me.
I do not want to rule out that this person may be right, but I also think he might be sharing this information not entirely without self-interest.

• Is there anyone here in the forum who has completed a similar project?
• Does anyone know a "desperate" company, or at least an committed one, that would realistically carry out such a construction?
• How would you approach such a project?

I had already planned to visit a structural engineer and, of course, have a new structural calculation done, since the units (e.g., newtons instead of kilograms) and load limits have changed. But if they are so fed up that such a request gets categorically rejected, that does not seem to improve anything either...

Even if it might not help much, I have attached the basement floor plan, the basement construction description, and some pictures.

PS: The basement blocks are HBL 50.

Thanks for your help
Berlinho

Given the current very strong demand for construction (building boom), I would assume that desperate companies with available capacity are either on the verge of bankruptcy and trying to stay afloat by accepting as many projects as possible, or they are simply poor-quality contractors.

What incurable diseases does a Streif house have? A house like that should last at least 100 years.

Building on existing basements is actually not that unusual. It happens quite often in our area.

Off the top of my head, I can think of one timber frame, one solid wood, and two concrete construction companies. None of them are shoddy builders or close to bankruptcy. This won't help you much anyway.

In my opinion, whether it is a new basement or an existing basement with structural engineering documents does not make a difference.

Berlinho schrieb:

I have a property in the southwest of Berlin with a prefabricated house from the company Streif Haus, fully basemented, built in 1970. My intention is to remove the house, keep the basement, and build two full stories on top of it.

Then go ahead, but let’s first discuss why you believe the existing house is unsuitable.

Berlinho schrieb:

After initial inquiries with construction companies, I was immediately told that they generally wouldn’t do such projects and [...] He himself (owner of one of the companies) said he doesn’t know anyone in the Berlin area who builds on existing basements, because it’s an “incalculable risk regarding warranty/guarantee.”

The market for construction companies is difficult enough to overview; you should actually be grateful for such self-disqualifications. An existing slab-on-grade (OKKD) is nothing more than a foundation slab. What does this “builder” normally do professionally – build butcher shops?

Berlinho schrieb:

Is there anyone here in the forum who has carried out a similar project?

Without claiming to be exhaustive – just nine weeks ago, I could name at least half a dozen:
https://www.hausbau-forum.de/threads/angebot-ueber-ytong-bausatzhaus-bau-auf-bestehenden-keller.39957/page-2#post-514506

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