ᐅ Moisture in New Construction: Drying the Shell After Rain – Risks and Proper Procedures
Created on: 6 Jan 2026 12:11
T
thegreensmile
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!
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!
If the roof is not yet installed, there is a risk that water will accumulate on the lowest floor and then rise up the walls. To prevent this, a damp-proof course is installed between the first and second row of bricks. It looks like this has been done in your case. This means that the rainwater should have only reached the lowest brick layer and slightly penetrated the masonry above.
We set up temperature and humidity loggers, which are quite affordable, to monitor the effects of ventilation and construction dryers. Fortunately, our masonry was dry, but the moisture from the interior plaster (almost 5000 liters) still needs to evaporate.
Ventilating during sub-zero temperatures helped the most. We first heated the house, then ventilated by fully opening windows for 20-30 minutes. We also have dehumidifiers, but they barely kept up, and the electricity meter was running fast.
Additionally, we switched to an external 22 kW oil heater. Electric heaters are far too inefficient.
We set up temperature and humidity loggers, which are quite affordable, to monitor the effects of ventilation and construction dryers. Fortunately, our masonry was dry, but the moisture from the interior plaster (almost 5000 liters) still needs to evaporate.
Ventilating during sub-zero temperatures helped the most. We first heated the house, then ventilated by fully opening windows for 20-30 minutes. We also have dehumidifiers, but they barely kept up, and the electricity meter was running fast.
Additionally, we switched to an external 22 kW oil heater. Electric heaters are far too inefficient.
T
thegreensmile8 Jan 2026 16:36Do oil heaters not release any moisture into the indoor air themselves?
Well, I’m wondering if it really makes sense to invest so much energy in drying out the building before plastering, when the plaster will inevitably introduce a lot of moisture back into the house anyway.
Well, I’m wondering if it really makes sense to invest so much energy in drying out the building before plastering, when the plaster will inevitably introduce a lot of moisture back into the house anyway.
thegreensmile schrieb:
Do oil heaters themselves not add moisture to the indoor air?
Well, I'm wondering if it makes sense to put so much energy into drying the building before plastering now, when the plaster will anyway reintroduce a lot of moisture into the house. Of course, oil and gas heaters release a lot of water vapor into the air and, due to their exhaust gases, are no longer suitable once the windows are installed. But there are good heaters that can be placed outside. We rented a Remko ATK 25.
I would be cautious about a wet wall because of the frost; it can damage the bricks.
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