Extension to existing semi-detached house - Security

Hello,
once again I am trying my luck, although the response to my inquiries has so far tended to be almost zero.

We want to extend an already existing semi-detached house (with a cellar), also with a cellar.

Now both the architect and the builder are pondering how and in what form the stabilization of the other house must be done.

Suggestion
1. "Set back" the neighbor's cellar, i.e. shorten it by 1m, pour a slab at the semi-detached house
2. Stabilize the walls of the neighbor's house somehow more securely (sheet piles??)

How much does something like this cost and how complex is it?
Who actually has to take care of it, shouldn't a semi-detached house be designed so that the other can be attached without problems?

Thanks
Hilaria

So moving back would only be possible if you own the other half of the house or if you could come to an agreement with the owner. The costs range depending on the region, size of the house, and provider from 80,000 (small, inexpensive region) to 350,000 euros.

Hello,

We want to extend an already existing semi-detached house (with a basement), also with a basement. Now both the architect and the builder are pondering how and in what form the securing of the other house must be done.

There is actually nothing to ponder, because...

Suggestion
1. Set back the neighbor's basement, i.e. shorten it by 1m, pour the slab against the semi-detached house

... costs roughly the same amount of money in total, aside from losing living space, as

2. Make the walls of the neighbor's house more stable somehow (sheet piling??)

supporting the existing building at the boundary. Foundations can only ever be placed on "natural ground level"; if this is not present, it must be created. At the moment your excavation contractor moves the excavator, he changes the original (in this case probably compacted) terrain...

Your architect and/or builder should not have to worry about this, but rather the structural engineer based on the results of the soil report.

How much does something like this cost and how complex is it?

That depends on how large/old the neighboring half is, which materials were used there, what the soil report says, what the structural engineer determines, and much more... but additional costs in the range of EUR 5,000 plus x are easily incurred.

Who actually has to take care of this, shouldn't a semi-detached house be designed in such a way that the other can be attached without problems?

Always the one who builds second; this is one of the main reasons why complete semi-detached houses in new development areas should ideally come simultaneously from a single source.

You are responsible to ensure that the existing property suffers no damage; you must commission the appropriate securing measures through your builder. Weren't you informed about this in advance? If it comforts you, if you wanted to build without a basement, you would usually have to spend more money.

Kind regards

@Jimmy80, I unfortunately do not understand your post at all

@Bauexperte, why would the construction be even more expensive without a basement?
The other semi-detached house has been standing for about 6 years and is 8 x 8.50 in size.

"Foundation can only be laid on natural ground," can you explain that a little more?

Why is moving back just as expensive? Sure, space is lost...

Thanks.

We have just done exactly that - demolished a semi-detached house and attached a new basement to the existing semi-detached house. We had to underpin the other half because our basement goes deeper - cost 2,000 euros per meter.

Hello,

@Bauexperte, why would the construction without a basement be even more expensive? The other semi-detached house has been standing for about 6 years and is 8 x 8.50 in size.

Because then you would have to support the entire length of the existing house down to the basement level. Such a step-down easily costs around TEUR 10 +/-

"Foundation can only be laid on natural ground," can you explain that to me a bit more?

The term ground surface usually refers to the natural ground surface, meaning the existing or “grown” soil. This ground surface has not been artificially altered by excavation or filling.

For the ground surface, there is for example a specific regulation in NRW for sensible adaptation § 9 Building Code NRW.

Why is stepping back just as expensive? Sure, space is lost ...

Firstly that, and secondly you have to support the ceiling to the ground floor at the earth-contacting parts as if there was nothing underneath it.

However, I consider the TEUR 2/per running meter mentioned by my predecessor to be exaggerated; nonetheless, it is not cheap.

Kind regards