ᐅ Will we have a moisture problem in the basement?

Hello everyone,

I hope I have chosen the right subforum, since insulation often involves moisture issues and thermal bridges, etc.
I am currently concerned about the temperature and humidity balance in our future stairwell. The groundwork is ongoing, so many things can still be changed if needed (insulation, doors, etc.).

The plan is for an open stairwell connecting the basement, ground floor, and first floor. The basement is cast-in-place concrete with 10cm (4 inches) perimeter insulation, while the ground and first floors are timber frame construction. The stairwell is located along an exterior wall, and this exterior wall (insulated with 10cm (4 inches)) is also exposed in the basement. The basement floor can be heated with underfloor heating, which can be individually controlled via a room thermostat.

Now my concerns: Since the three floors are freely connected, there will always be a temperature gradient from top to bottom. This means, for example in summer, the warm, humid air generated by bathrooms on the upper floor will cool down, sink to the basement corridor, and cause condensation. The same applies to moisture coming from the open kitchen on the ground floor.
In winter, the same issue arises, but the underfloor heating in the basement corridor can be activated to counteract the temperature gradient. However, this would result in a noticeable temperature difference between the heated basement corridor and, for example, the unheated technical or laundry room in the basement.

So my question to you: Is this a hypothetical problem or a realistic concern? Has anyone experienced a similar situation and can share insights? How could this be addressed if necessary? (I would prefer to avoid fully enclosing the basement stairwell.)

Thanks for your help and best regards,
Tobias

A mechanical ventilation system with heat recovery is a very useful feature 🙂

MaytO schrieb:
For example, in summer, the hot humid air that forms upstairs due to bathrooms cools down, sinks into the basement corridor, and condenses. The same applies to moisture generated in the open kitchen on the ground floor.

Why should the warm air upstairs cool down in the summer? Why would it first cool, then sink down, and finally cause condensation there?

Of course, there will be a slight temperature gradient. The same happens with doors to the stairwell, which are not airtight either. If the basement wall at the stairwell is exposed, such as on a hillside, I would probably opt for 140mm (5.5 inches) insulation to prevent any dew point from being reached on the interior surface.

Between the mechanical room and the basement corridor, there might be a temperature difference, but only because the corridor is colder. The waste heat from the equipment in a modern basement should be enough to keep it temperate.

Ok, thanks for your assessment. I won’t worry about it anymore.
Increasing the basement insulation to 140mm (5.5 inches) is unfortunately not possible without complications or additional work due to the threshold construction of our house.