ᐅ New Construction – Is High Humidity Still Normal?

Good morning everyone,

We finally moved into our new build at the beginning of the month.
We are struggling with high indoor humidity, and I am unsure whether this is just residual moisture from construction or if we need to take action.

Here are some key details about the house:
- 113 m2 (1,216 sq ft) detached house without a slope and no basement
- 30 cm (12 inches) aerated concrete blocks, drywall partitions on top
- Underfloor heating
- Heat pump
- Click vinyl flooring in all rooms except the ground floor hallway (which is still without flooring and will be installed once all the boxes are out of the hallway)
- No mechanical ventilation system (we now realize this was unwise, but it never came up during construction, so we never considered it)

In mid-August, we had a small water damage issue on the wall in the guest toilet on the ground floor. Fortunately, the source was quickly found and fixed. Our plumber then turned on the underfloor heating on the ground floor for a week to help dry out the moisture faster.

Currently, I ventilate 5-6 times a day.
The heat pump is still off because all rooms are still above 22°C (72°F).

Despite regular ventilation, the humidity remains consistently above 65%. At night, it rises to 75%.
We bought an electric dehumidifier, which is in the ground floor hallway, but it only manages to reduce the humidity to 60%. As soon as it is turned off, the humidity immediately rises again.

My husband says I should be patient because it’s normal for moisture levels not to drop quickly in a new build. He says to only worry if it hasn’t improved by next year.

However, I am concerned that we might have missed another water damage issue and that mold could develop in the house soon.

Is it worth investigating the cause, or is this really just residual construction moisture?
If this is normal, do we need to do more to control the humidity, or is a winter with high humidity not a problem as long as we continue ventilating regularly?

Best regards,
Sina

Sina_89 schrieb:

Despite regular ventilation, the humidity remains constantly above 65%

I have the same – renovated old building. That’s normal at the moment.

Sina_89 schrieb:

At night, it rises to 75%.

You exhale a lot of moisture. The house does too (screed, plaster, etc.). And you don’t ventilate at night.

So yes, currently no reason to worry.

No cause for concern, but also no reason to do nothing.

In the past, wealthy people or investors would let houses to temporary residents for about 2 years to allow the building to dry out. Only after that period would the property be rented out or occupied by the owner.

Make sure to ventilate properly and thoroughly. Use short, intense ventilation and cross-ventilation. From now on—or already starting—heat well despite ventilating. Don’t be stingy with heating.

In summer, we also always have around 65% humidity… it’s just damp, muggy air outside. As soon as it gets consistently cold, the indoor humidity drops significantly. We have been living in the new build for 7 years… everything is fine, no mold.

Thanks for the answers, that really puts my mind at ease ^^
I’ll keep airing the room thoroughly and turn on the heating this week.

Did you install a ventilation system?
Shortly after moving in, our average humidity was only 55%.
Now, a year later, it’s below 45% on average during the day. In midsummer, it never exceeded 60%.
However, we had a 9-month delay before moving in.

Without knowing how extensive the water damage really was, it’s hard to say if “one week of underfloor heating” is enough to dry it out.
Did the water get into or under the screed? Hopefully, there is cement screed installed in the bathroom?! Who inspected the damage and decided what to do? The party responsible?

To me, it sounds like you should trust your instincts and take a closer look.