ᐅ Pay attention to the concrete slab foundation when building on a special or challenging site.

Hello everyone,

We are planning to buy a plot in a new residential development. Construction has not started yet. The building start date is 2015.
The soil was replaced up to 4 meters (13 feet) deep due to contamination. Then, sand was added layer by layer, and each layer was compacted with heavy machinery. Local residents confirmed this to us. Finally, topsoil was applied and compacted as well. You can actually walk on it without sinking.
What do you think? Does it make sense to build on this, or will the ground still settle enough to likely cause settlement cracks? Should we expect additional costs for the foundation slab?
Best regards, Xinette

Our building plot was prepared in a similar way.
It was a former factory site, with up to 6 meters (20 feet) of soil replacement (less in our case) and layered backfilling, including compaction with heavy machinery.

The soil report then provides certainty about any additional measures that need to be taken.
If I remember correctly, the concrete slab had to be reinforced with extra steel mesh and an additional layer of crushed stone had to be added.
If everything had been fully calculated for us, all of this would have cost around 4,000 euros.
However, I have also heard from other builders in the development area that they had to pay more because a greater amount of soil needed to be replaced.

The best advice is to have a soil investigation carried out (preferably before purchasing). Only then will you know if and to what extent additional costs for groundworks (e.g., soil replacement) or the foundation slab can be expected. This also depends on whether you plan to build with or without a basement. It might also be advisable to carry out a contaminated land survey.

In our case, the developer had to provide the responsible authority with proof/report confirming that the contaminated sites had been cleared. Only then were the building permit/planning permission applications processed.

At least the contaminated soil has been removed. Soil samples were taken continuously. We will check to see if there are any other samples available. However, I also believe that despite stabilization, there is still a possibility of further settlement.
Best regards, Xinette

You will need the soil survey anyway, so it’s not a big deal. Unfortunately, we couldn’t have a soil survey done before purchasing the plot and signing the loan agreement. This was one of the major unknowns in our budget planning.