ᐅ Extending Basement Walls

Good evening,

I am currently planning the renovation of a house and am facing a problem for which I need some helpful advice.

Here is the situation:
The house has three floors and is built into a slope. Therefore, the lower floor is open on one side (facing the garden). On the opposite side, this floor is embedded into the ground.
The house is not fully basemented. The room that is dug into the slope is surrounded by a wall approximately 50 cm (20 inches) deep measured from the ground floor slab, and is nearly as high as the ceiling, filled up with earth. It’s a bit difficult to explain, but I hope it’s somewhat clear.

Now, I would like to convert this sunken room into an additional basement space, but I would need to extend the outer walls downward to bring them level with the adjacent wall.

My question is whether this is even possible and, if so, what rough costs I should expect. Of course, I will have it done by professionals, but before requesting a quote, I want to have a general understanding of what I’m getting into. To make it a bit clearer, I have attached a side view of the house. The plan shows that the external wall is too short.

I would appreciate any advice.
Best regards

You want to excavate the "room" in the lower left corner? I don't think that will work. That is not an external wall but a strip footing. If you dig that out, the entire structure might collapse.

I share that concern. I assume it might be possible with an appropriate support structure, but it would probably still be risky and quite expensive.

You should definitely consult a structural engineer or architect for this.

In addition to the structural issues, you will probably also need to consider legal regulations regarding thermal insulation and similar requirements. I don’t believe this can be implemented with a good overall cost-benefit ratio.

Hello,

StefanBW1 schrieb:

I am currently planning to renovate a house

Have you hired an expert or an architect?

StefanBW1 schrieb:

My question is whether this is even possible and, if so, roughly what costs I should expect.

Anything is possible, but it will cost 😉

Since the excavation is quite extensive, the structure will need to be supported step by step, which in turn makes the removal of the existing soil, the installation of concrete for the foundation slab, and the connection to the existing building more complicated.

Aside from the fact that you should clarify the expected costs with a professional on site, a structural engineer must absolutely be called in to inspect and assess the entire project. It might even be necessary to involve a geotechnical engineer.

Overall, the costs are unlikely to be justified by the benefits.

Regards, Bauexperte