Single-family house extension to existing house - foundation step down

Hello,

the plan is to add another detached house (approx. 8.50 x 7.50m) to the existing house (approx. 8.50 x 10m).

The old house has a basement, we want to build without a basement (timber frame construction).

As far as I know, you have to go down to the depth of the basement of the old house and create a stepped foundation.

What are the approximate additional costs compared to a normal slab? Are we talking about 1,000 or 10,000 EUR? Can you even roughly say?

Thanks and best regards

As far as I know, you have to go down to the depth of the basement of the old house and make a stepped foundation.

I see no necessity for that according to your description. Garages are also regularly built without basements directly adjacent to a building with a basement. Attached houses, one with and one without a basement, are actually unproblematic as long as the one without a basement is the one built later.

The foundation must be founded on the native soil. Immediately following the basement, there is always the excavation pit with backfilled soil, which is usually not compacted to the level of native soil. This must be checked using appropriate methods, e.g., with a dynamic probing. If necessary, the excavation pit must indeed be founded up to the top of the native soil, e.g., with lean concrete up to 80 cm below ground level in frost-free depth. In other locations, this depth is reached without deep foundation. The decision is the responsibility of the planner or structural engineer. Obtaining the information is the client’s task. The additional costs cannot be specified without knowledge of the exact circumstances; however, they will realistically be between € 1,000 and € 10,000.