Humidity in basement apartment

Hello,

my tenant sent me the following photo from my basement apartment. Apparently, there are moisture problems.

This is an exterior wall.

What is the correct procedure here (4-family house with 4 owners)? Initially, hire a building expert at your own expense to determine the cause (it could also be improper ventilation, etc.).

How would you proceed here?

Simply measure humidity over a longer period of time! Then you’ll know whether it’s the wall or the ventilation. "Leihen Meinung" Here I suspect an interplay of incorrect ventilation on cold walls including drying laundry indoors.

That means I should tell the tenant that we are going to measure the moisture for a week first? That is done by a building surveyor with the appropriate equipment, right?

In the end, it will probably fall on me or the homeowners' association; how am I supposed to prove incorrect ventilation to a tenant.

Well, if you don't want to get started right away, you can provide him with a hygrometer, preferably one with a log function. And get a device to measure wall moisture.

But it depends on the tenant; if he already threatens with a lawyer, then call in a professional.

And explain to him how to ventilate properly.

Never leave windows on tilt.
At least 3 times a day, open all windows and create a draft.
Room temperature must be at least 19 degrees, so a cold sleeper will have problems here.

I had the same problem but with my old apartment.
When I lived alone, no problem, but when there were two of us and double the amount of laundry and more people breathing and sweating, mold started to form on the exterior wall.
Then shift work as well, so windows closed for 15 hours in the bedroom, etc.

First measures: bought a dryer.
Then turned on the heating so the room doesn’t cool down.

And when building the house, it was clear to me that it would not be built without [Kontrollierte-Wohnraumlüftung].

Even more photos have come from the tenant......

I tend to commission a building surveyor specializing in moisture damage.

Someone who writes something like this on their website:

"Detecting and specifically treating moisture damage

Our building surveyor's office specializes in the detection and assessment of moisture damage on and inside buildings and on mold infestation in interior spaces. Our building surveyor operates in the greater Düsseldorf, Essen, Cologne, and Wuppertal areas and beyond by arrangement.

Moisture damage is among the most common building damages on and inside buildings. Moisture damage can significantly reduce the value of a property. Moisture damage can lead to consequential damages such as mold infestation.

Molds are microorganisms that cannot be seen with the naked eye and are usually harmless. However, if the mold concentration exceeds a certain level, mold infestation can lead to significant health impairments and, in addition to strong odor nuisance, have allergenic, infectious, and toxic effects.

An expert for mold or a mold assessor can detect mold infestation by measurement or sampling even when it is not yet visible as typical mold infestation on the wallpaper.

Before professional remediation, the cause of the moisture damage or mold infestation should first be investigated. It is important to consider all possible factors. Simply reading moisture measuring devices is usually not sufficient.

Independent advice instead of a sales pitch! Remediations of moisture damage should be well thought out, goal-oriented, and sustainable. Do you have an offer and are unsure? Save money through our experience with moisture damage.

When mold damage occurs in apartments, disputes between tenants and landlords can arise quickly. Is the heating and ventilation behavior of the residents responsible, or is moisture damage due to a construction defect the cause? The inspection result can be recorded and documented by the building expert in a building damage report. Afterwards, a solution can usually be found quickly and in a goal-oriented manner, also in a discussion with all parties on-site."

As a rule, the expert can also determine what the cause is. Incorrect ventilation, or is the wall wet. So an expert is the right way for me. This also shows the tenant that something is happening. At the same time, I would buy such moisture meters for the tenant. There are some that blink when the humidity is too high. They are actually just the right thing. Then even the dumbest person knows when to open the windows.