ᐅ How much additional cost is expected based on the structural engineer’s calculations?

kati1337 schrieb:

You really planned to just dig a basement directly into the ground without any waterproofing or anything else, and just install drainage around it?
If that was really the plan, you urgently need someone to advise you. I can’t imagine the builder wasn’t aware beforehand that this wouldn’t work.

Yes, we do want waterproofing, of course, but now we need the "black tank" (cavity waterproofing), which will definitely add about 15,000 euros in extra costs.

kati1337 schrieb:

I can’t imagine that the construction manager wasn’t aware beforehand that this wouldn’t work.

They were aware. But why should they inform the unexperienced client about this in advance? That’s basically how profit is made in construction.

If I were reviewing such a change order, the first thing I would ask is what has changed in the geology compared to the initial calculation.

Is the groundwater level now higher?

Is this a fixed-price offer? How exactly are the basement and drainage specified?

Lauralila88 schrieb:

The price included the standard waterproofing and drainage, but now we need a black or white tank waterproofing system.

What exactly is stated in the offer / contract?

Lauralila88 schrieb:

Yes, waterproofing of course, but now we need the black tank waterproofing, which certainly adds about 15,000 euros in additional costs.

I thought the black bitumen coating is called black tank waterproofing. Hmm...

Lauralila88 schrieb:

Since you seem to know your stuff, I wanted to ask roughly how much soil removal costs, no one could tell me.

Not as well as you might think, as you can see. For us, without a basement, there was quite a lot of soil—over 100 cubic meters of loose earth. We had to hurry to get it removed because the neighbors wanted to start as well.
We found a buyer via eBay Classifieds, but the plot was about 20 meters (12 miles) away, so with daily trips by truck, not much could be removed at once.
My husband then simply asked a construction company on site, who removed the soil for 2,500 euros. That was 10 years ago, and nowadays excavation of a basement would probably cost between 8,000 and 10,000 euros. Maybe another forum member has more precise information. Unfortunately, I can’t think of anyone here actively building with a basement, except for hillside projects like @kati1337. Precisely because of the enormous costs, basements are now often omitted.

hanghaus2023 schrieb:

Is this a fixed-price offer? How detailed is the description of the basement and drainage?

I assume the basement is listed as a separate item in the house offer, @Lauralila88?
How much does the basement cost in the offer?

I’m interested as well. What type of waterproofing was planned if it wasn’t a bituminous membrane? Isn’t that the basic standard for new construction?

I can’t see the builder as reliable with this kind of business practice. Usually there’s a reason they’re cheaper than Heinz von Heiden or Massa Haus. They offer low prices but exclude many important items that a layperson might not notice.

First, the mysterious waterproofing is “upgraded” to the technical minimum. Then the house suddenly becomes more expensive due to the structural engineering. Why? What has changed?
If you want to stick with the contract, I would seriously consider bringing in someone knowledgeable to help.