ᐅ New single-family house construction with a basement and external basement entrance

Hello,
we are planning a new build with a general contractor.
The house will be constructed using conventional, single-layer masonry with porous bricks—so a solid structure.
The general contractor also planned the basement. It consists of a waterproof (WU) basement with perimeter insulation.

Since we have a slight slope on the site, we considered having a basement apartment. Although we could install windows there, a separate entrance seems to be problematic.

The basement access would not have natural drainage and would need to be connected to the sewer system with a backflow prevention valve.

The general contractor strongly advised against doing this. (He can design it that way in principle, but we will see that we cannot actually build it like that.)
The soil survey indicates hydrostatic water pressure and requires sealing up to the ground level.

I would like to know if it is really impossible to create a separate basement entrance when there is hydrostatic water pressure?

Ask the general contractor whether the basement will be constructed using waterproof concrete elements or by cast-in-place concrete with formwork. We also stumbled over the term "WU basement."
A basement staircase is indeed difficult to seal properly.

Thank you for your reply.
The description states: "Basement exterior walls, at the discretion of the contractor, made from approximately 24cm (9.5 inches) thick cast-in-place concrete walls or from prefabricated double walls with infill concrete, totaling 30cm (12 inches) in thickness."

But what would happen if the basement entrance is not watertight? Water can’t flow into the entrance from outside. I would also put a roof over it. So, in the worst case, water could only push from the wall into the basement entrance.
The water would then collect at the bottom and flow into the door. To prevent this, I have installed a drain there.

Water can only enter the building through the basement door then, right? The waterproof (WU) basement is otherwise sealed.

theking1102 schrieb:

The water would then collect at the bottom and run into the door. That’s why I installed a drain there to prevent this.

If water stands at the basement stairwell, you need a watertight bulkhead door to prevent any water from entering the basement.

Where is the drain supposed to discharge? Water comes out there but doesn’t drain away, or do you have a pump system planned?

theking1102 schrieb:

Thank you for your response.
The description states: "Basement exterior walls at the contractor’s discretion made of approximately 24cm (9.5 inches) thick cast-in-place concrete walls or prefabricated double walls with concrete infill, with a total thickness of 30cm (12 inches)."

There is a significant difference between using prefabricated wall elements (semi-finished components) and on-site formwork. I would not leave that decision to the contractor. I can only advise you to choose the 24cm (9.5 inches) cast-in-place concrete method. It has decisive advantages, not least for potential renovation issues in case of leaks. When building with prefabricated elements, many more problems can occur (interior surface of the precast parts not rough enough, insufficient pre-wetting during concreting, incorrect support installation, joints sealed with expanding foam, etc.). A 24cm (9.5 inches) monolithic wall cast on properly installed joint tape and adequately compacted is unbeatable.

If water pushes into your basement entrance, whether through the stairs or the wall, either the floor covering or the plaster will deteriorate, and if neither is present, it will soon look like a wetland. Your general contractor should only undertake this if they have relevant experience with it.

Are you planning to appoint an independent expert or construction supervisor? In my experience, that is more important than the basement stairs themselves.

I have not planned a pump system, but there is a drain with a backwater valve.
Additionally, the drain is located about 80cm (31 inches) above the backwater level (i.e., street surface level) due to the hillside location. The sewer is significantly lower than the street surface level.

@Allthewayup
Thanks for the tip about the in-situ concrete. I will make sure to consider that.
We are including the construction monitoring services from Tüv Süd in our plans.