ᐅ Moisture in New Construction: Drying the Shell After Rain – Risks and Proper Procedures

Hello everyone,

We are currently building a single-family house in NRW. We started around June/July.
The shell was completed around calendar week 46. It was built with hollow bricks, T9, 36.5cm (14 inches) thick. About a week later, we had our ring beam installed. Unfortunately, there was a delay with the wood, and the roofers were only able to make the house watertight 3–4 weeks later. This means the shell was exposed to a lot of water during that time.
By now, the house has been completely sealed with roof and windows for about a month. We have just started with the electrical work, but unfortunately, some walls still show darker spots where I suspect dampness. We are also having difficulties drying the plaster for the outlet boxes in those areas.

My concern now is that I might face problems with moisture later on — such as cracks in the walls and mold.
At first, I ventilated the house by keeping the windows open from morning until evening, but then I learned that ventilation needs to be done more carefully, for example, considering the dew point between inside and outside. Since I was uncertain, I stopped ventilating and have been using dehumidifiers for the past two weeks.
Currently, I have one dehumidifier and a 2 kW heater in each of the two children’s rooms. Twice a day, I empty about three quarters of the water tank.
My plan is to move the dehumidifiers to other rooms after one week and to “treat” the entire house like this for a total of four weeks. I also have an electronic moisture meter to check the walls, but it is a simple device costing 25€, and it only measures electrical conductivity, so I am skeptical about the accuracy of the readings.

My question to you is: am I handling this the right way? Is it efficient? What is the risk of wall cracks or mold?
Can I safely continue with the electrical work, heating installation, and possibly plastering, or should I wait until the house is completely dry?
I am happy to provide pictures if needed. I appreciate any help!

thegreensmile schrieb:

The building was constructed using T9 perforated clay bricks, 36.5cm (14 inches) thick.

Were these covered on top when it rained? This is a regulation that is often overlooked.

And believe me, with the plaster you will get enough moisture into the house, especially together with the screed.

tomtom79 schrieb:

Were these covered when it was raining? That’s a regulation that is often overlooked.

I covered the window sills myself before the windows were installed, and the ring beam was done fairly quickly.
I’ll upload some photos.

As far as I know, unfilled hollow bricks do not necessarily need to be covered to protect them from rain—unlike filled bricks. They were unfilled bricks, right?

How is the weather at the moment? As long as there is no severe frost, I would recommend alternating between thorough ventilation and immediately running the dehumidifier afterward. Don’t worry about any cracks. Normal shrinkage cracks at material joints are almost unavoidable. Just today, after nearly two years, I noticed a new shrinkage crack in the interior plaster. With the ongoing cold, constant heating, and 24/7 ventilation, the humidity drops significantly, and the last bit of moisture escapes.

I see an opening toward the attic? Is that a cold roof? If so, you should definitely temporarily seal it with an XPS board before plastering or applying the screed. Otherwise, moisture will rise during heating and condense there, which usually leads to mold.

Back to your damp bricks. Our garage wall looked exactly like the wall in your photo. However, this did not affect the plastering. Everything will dry out over time. In addition to the dehumidifier, I used a few fans to keep the air moving inside the house and directed toward the dehumidifier. This way, mold hardly has a chance to ever find "suitable conditions."

They were hollow bricks, right?

Exactly, hollow bricks. Since I wasn’t sure, I covered them anyway, even though they also absorb water from the sides.

About the weather: It’s cold and snowing a lot. However, in the later evenings, the temperature inside the house is always above freezing. Unfortunately, I don’t know what it looks like overnight.

alternating between intensive cross-ventilation and then immediately turning on the dehumidifier

How can I do cross-ventilation properly? Maybe I’m making it too complicated...

I see an opening towards the attic?

There will be a folding attic ladder at that opening. I also plan to insulate both the roof pitch and the ceiling on the upper floor. Then I will finish with a drywall panel. Should I do all that before plastering?

Besides the dehumidifier, I also used a few fans to keep the air moving inside the house

I’m also trying to work with two dehumidifiers to create circulation. But what Tomtom79 said also makes sense. Plastering definitely brings a lot of moisture into the house.

I am definitely very confused.

Allthewayup schrieb:

To my knowledge, unfilled hollow bricks do not necessarily need to be covered to protect them from rain—unlike filled bricks. These were unfilled bricks, right?

The Wienenberger T9 hollow bricks without filling definitely need to be covered, according to the datasheet. Especially at below-freezing temperatures, water can cause the bricks to crack. Additionally, the water damages the structure of the bricks and weakens them.

Unfortunately, I cannot add any links.

Now we just have to hope they dry out.