ᐅ Building Site: Extensive Fill or Is It Better to Have a Basement with Excavation?

We own a sloped plot (about 3 m (10 ft) height difference between the street and the future garden level at the basement) and originally planned to build with a residential basement because the land slopes downward from the street.

However, today we visited the site with an experienced civil engineer who specializes in foundations for prefabricated houses. He believes it would be more practical and cost-effective to build without a basement and instead raise the ground level by up to 3 m (10 ft) using recycled gravel. Even if that requires around 500 m³ of gravel.

This could be well compacted with a roller, and settlement would not be an issue. The parking spaces and the house facade would need to be filled in anyway to reach the entrance.

Otherwise, due to the relatively high position of the sewer connection, we would need a pump system in the basement, and disposing of the excavated material (clay soil, about 200 m³) would be very expensive in the region because there are almost no landfills available (35 €/m²).

Who has experience with these issues? I thought a basement was usually more cost-effective and safer on sloped plots than large-scale fill?

For landfill fees, it’s better to follow the civil engineer’s advice. A lifting station for sewage is probably a bad idea as well.

It's not rocket science. The question is how to raise the house in a way that you can still make use of the outdoor space.
As far as I know, the costs for soil disposal in Baden-Württemberg are the worst. Thanks to Stuttgart 21. All the landfill sites are full, so they charge a lot of money. On top of that, transport costs are higher because the soil can no longer be taken to the landfill just around the corner.

Hello Thierse

I tend to prefer having a basement. I’m quite conservative in that regard.
My house is positioned on the plot in a similar way. Sure, 35 euros per m³ (cubic yard) for the excavation is quite a bit. But filling 3 meters (10 feet) with recycled crushed limestone (RCL) is not exactly cheap either.
I have my double garage behind the house at basement level, and my terrace is on top of the garage. I’m quite happy with this setup.
And if you don’t necessarily need a toilet in the basement but only a washbasin and a washing machine, a sump pump is definitely sufficient.
Calculate everything carefully. Even if the basement costs a bit more, it would definitely be worth it for me.

Steven

You will hardly see the 500 cubic meters. Expect significantly more. The net volume you need to fill, multiplied by about 1.3 to 1.5, is the calculated RCL volume. This is the compaction factor.

Then, you will have to remove some of the clay soil anyway, as you cannot build on the topsoil.

You also have to consider a 45° slope angle, meaning an additional minimum of 100 to 200 cubic meters on top of that.

I can provide you with 1900 m³ (2500 yd³) of soil if you want.
Disposal here in Baden-Württemberg is a nightmare.
Do you have a soil investigation? You are quickly in Z0* or Z1.1 categories, and then you can easily double your disposal costs.