ᐅ Watertight concrete basement for living space

Good evening,

I have received a quote for a waterproof concrete foundation (“white tank”), 10m x 10m (33ft x 33ft), for over €50,000.

I want to use part of the basement as a home office and bathroom. I researched online and found that the area would need to be insulated.

1. What exactly should I expect in this regard?
2. Does the insulation need to be installed on the outside or inside?
3. The waterproof concrete foundation is basically completely sealed. If you live in that space, how does the moisture generated by a person get removed? Is it necessary to install a ventilation system?
4. What would the approximate additional cost be? Around €1,000, €10,000, or more?

Thanks for your help.

For us, the additional costs for a house with a built-up area of 90 m² (970 ft²) are around €18,000. This includes insulation, heating, an increase in floor-to-ceiling height, and the connection for controlled residential ventilation.

Our basement has also been designed as a living basement, with additional costs exceeding 30,000 euros.

This includes

external insulation,
internal insulation,
controlled mechanical ventilation for living spaces,
exposed piping under the plaster in the basement as usual,
underfloor heating,
windows,
and more.

Hello,
the question about additional costs depends on the basic standard you are starting from. A waterproof concrete basement (white tank) should definitely have insulation; otherwise, you end up with a cold, damp cave down there. We have 10 cm (4 inches) of perimeter insulation, which is more than enough.
For a finished ceiling height in an office, you should have at least 2.25 m (7 ft 5 in). A standard 2.5 m (8 ft 2 in) height is of course nicer but also more expensive. As a rough estimate, you can expect about 150-200 € per centimeter.
If you already have a mechanical ventilation system with heat recovery planned, the extra costs to connect the basement are marginal and something you should do anyway, regardless of whether it is a living space or not. If you have not planned for such a ventilation system so far, that means an additional 10,000-20,000 €.
Heating will cost you another 4,000-5,000 € for the basement.
Piping and wiring should be installed inside the walls and concealed, whether it is a living basement or not. Important: you generally cannot install concealed piping on the exterior walls of a waterproof concrete basement. Chasing into the concrete is not a good idea.

Best regards,

Andreas

andimann schrieb:
Pipes should generally be installed inside the interior walls, concealed under the plaster, regardless of whether it is a basement or not.

Depending on who builds your basement, the interior walls may also be made of concrete. With Glatthaar, you can have conduits installed in advance for an additional cost. However, if the interior walls are masonry, installing pipes concealed under the plaster is of course not an issue.

RobsonMKK schrieb:
Depending on who builds your basement, the interior walls might also be made of concrete.

Sure, that does happen (and given this morning’s election results, it might not be a bad idea to reinforce the basement like a bunker). However, with the providers I’ve spoken to, the interior walls in a waterproof concrete shell were always made of brick. That seemed to be more common...

Best regards,

Andreas