ᐅ Getting Moisture Out of a New Build – How to Ventilate and Other Related Topics

Hello everyone,

The shell of our house was recently completed. Our regional window supplier had a delay with a larger order, so we received our windows just 3 1/2 weeks after measuring—shortly after the roof structure was finished. In my opinion, this was almost too early, but I wasn’t given much choice since otherwise we wouldn’t have gotten them this year. Naturally, the house still contains a lot of residual moisture. The floors (especially in the basement) are now dry—or at least they look dry. However, many bricks (especially in the basement) are still dark-colored and damp. I’m also measuring a humidity level in the basement air of about 84%.

About the house: The basement is a waterproof concrete basement (WU-basement). The interior walls and all floors above ground level (ground floor and upper floor) were built with Poroton blocks.

Now to my main questions:
- What is the best way to ventilate? Currently, I have all basement windows tilted open. On the ground floor and upper floor, I have some windows (on opposite sides) open to create cross-ventilation. Is that sufficient?
- Following up on that: I still need to insulate the top floor ceiling with EPS035 (the insulation arrived today), and a waterproof membrane needs to be installed in the basement. When is the best time to do this, or how long should I wait before proceeding? I want to avoid trapping moisture underneath and causing mold in the end.

I’m interested in your opinions and how you handled similar situations during your build.

Kind regards,
XxTankerxX

You need large dehumidifiers and fans... just airing out by opening and closing windows takes too long.

Also, even where you no longer see moisture, the walls are probably still too damp.

Does anyone already have dehumidifiers running?

Next week, night frost is forecast frequently (down to -5°C (23°F)) – shouldn’t that accelerate the drying process?

Heating and regular short-term ventilation work the same way in winter. Without heating, you won’t be able to remove the moisture.

A dehumidifier is used in the humid midsummer or when you don’t have time to ventilate briefly three to five times a day. In winter, use a dehumidifier together with heating.

Oetzberger schrieb:

Heating and regular airing out by fully opening windows works just as well in winter. Without heating, you won’t be able to get rid of the moisture.

Dehumidifiers are used in hot and humid midsummer or when you don’t have time to air out fully three to five times a day. In winter, dehumidifiers work best combined with heating.

Without heating, it’s currently difficult. We want to install a small wood stove for work purposes, but it will probably only be used on weekends when we are on site. Airing out fully three to five times a day is really not possible — I don’t work at my future home. So, a construction dryer for one to two weeks? How much power do those usually consume? Around 1 kW?

An electric fan heater combined with one or two tilted-open windows is the energetically inefficient option. The fan heater plus the dehumidifiers is the more efficient choice. Your local rental service can tell you which is cheaper, including electricity costs.

It is possible that the waste heat from the dehumidifiers alone is sufficient, so you might not need any additional heating.