ᐅ Built-in cabinets partially on exterior wall – risk of mold?

Hello everyone,

We have been living in our new house since October 2024. The shell and roof were completed at the end of 2023, interior plastering was done in March 2024, and the screed was laid in April. So the house wasn’t built extremely quickly, and it’s quite dry; I have a hygrometer in every room, showing around 40 percent humidity. Of course, it’s winter, and all rooms are heated to 21-22 degrees Celsius (70-72°F) with underfloor heating. Each room is also mechanically ventilated.

About the problem: At the time, we thought built-in wardrobes were a good idea, so we installed quite a few. They look great, but one wardrobe worries me especially. Back then, we weren’t aware of mold issues at all, and even the carpenter still doesn’t think it’s a concern. But in our dressing room, there is a wardrobe fitted flush with the ceiling, floor, and both sides—completely sealed. The back and one side panel of the wardrobe face interior walls, but one short side panel faces an exterior wall. And that’s where you often hear about problems! By the way, our exterior wall has a U-value of 0.25.

So, out of concern, I drilled a hole in the very thick back panel of the wardrobe, and here comes the next shock: between the wardrobe and the (interior) wall, there is maybe only 2cm (1 inch) of space. Since the wardrobe has a side panel covering the exterior wall side, I suspect there is more room there—maybe 5cm (2 inches)—but I can’t say for sure.

I bought a hygrometer with a probe and inserted it through the hole in the wardrobe to reach behind the back panel, almost down to the floor. I’m currently measuring 21 degrees Celsius (70°F) and 58 percent humidity there. In the room itself, it’s also 21 degrees Celsius but only 40 percent humidity. Where does this difference come from? Residual moisture in the wall? Before moving in, I measured all the walls, and they were dry (of course, those moisture meters only penetrate about 4cm (1.5 inches) deep).

Do these values already indicate cause for concern? Or is it warm enough behind the wardrobe, considering there is underfloor heating everywhere? Will it get worse in summer? What should I do now? Drill more holes? Leave it as is and occasionally “smell” (as silly as that sounds)? So far, I can’t hear, see, or smell anything!

I’m close to having the wardrobe completely removed and cut apart so it can be reinstalled with more space from the wall. Is that necessary?

I’d appreciate your advice!

Jschm88 schrieb:

do these values already cause concern?

No. The exterior wall (and the cabinet) in a new build should always be warm enough to prevent mold growth. You can calculate this yourself using a dew point calculator available online.

You can install a mechanical ventilation system. Quiet computer fans with humidity control provide permanent air exchange and solve the potential problem without major remodeling.

Hi, I understand the theory behind it, but I don’t actually know the wall temperature. I drilled a hole at the top inside the cabinet. I could drill another hole at the bottom and then measure the wall temperature multiple times with a laser device that I still need to buy. Is that the idea? Or is it unnecessary because it’s a new build?

Where does the difference in relative humidity of 20 percent between the room where the cabinet is and the gap behind the cabinet wall and the masonry come from?

Regarding ventilation: I can’t do that because I don’t have any space behind the cabinet. I only have a baseboard with a gap of about 2cm (1 inch), so there’s no room for a fan back there. Or is that not what you meant?

Jschm88 schrieb:

I understand the theory behind it, but I don’t actually know the wall temperature.

In new construction, with the temperatures you measured behind the wardrobe, the wall should have an indoor surface temperature of about 20°C (68°F). You can use this value for your calculations.

Jschm88 schrieb:

Where does the 20 percent difference in relative humidity between the room where the wardrobe is located and the gap behind the wardrobe and the wall come from?

This is due to residual moisture and lack of ventilation (although the latter is not initially a problem).

Okay. So according to you, no action is needed. I will monitor the moisture, which should continue to decrease over the next few months. As long as the temperature behind the cabinet stays above 20°C (68°F), there should be no mold. Additionally, I occasionally notice a smell.

In conclusion: the sensor is now located behind the back panel of the cabinet, which is adjacent to an interior wall. However, I don’t think the measured values will be significantly different about 30cm (12 inches) further to the left, towards the exterior wall, right?