Basement odor transfers to objects: leather, cartons, fabrics. Mold?

Good day,

we live in a multi-family house. In the basement, there are eight privately used rooms and a few technical/common rooms, all connected by a corridor. In two basement rooms, a moisture problem has developed over the past 3-9 months (we have lived here for several years). About the rooms:

- the rooms have one or two exterior walls (corner room)
- the rooms have no window, no light shaft, or similar
- the rooms are connected by openings in the masonry (2 x one brick in the corners as a "hole" to the next room, see photo)
- current outside temperature 5 - 10 degrees, basement room 12 degrees
- the temperature in the common corridor that connects everything is higher, 15 - 16 degrees
- humidity 75 - 80 %, in the common corridor <60 %
- a bowl with salt absorbs the moisture (slightly sticky)
- the rooms smell musty
- the walls are not cluttered

The photos show the discolorations on the exterior walls. The wall is not wet, not damp. When running your hand over it, the hand remains clean (possibly dust, paint/stone particles).

Our problem is that we can no longer use some items. Two leather chairs, leather goods, suitcases, because they have absorbed the smell and it can no longer be removed. However, this is not the main issue. Still, we see it as a sign that something is not quite right.

The house itself is surrounded by a drainage system (40cm wide around the house). Shafts on the property are full. Everything on the green area feels wet, even when it is not raining. Could it be that it is due to a faulty drainage? That the shafts do not properly drain the water?

Or is it simply condensation moisture (opinion of the property management)?

Anyone who can report something, maybe has personal experience or is an expert, is welcome to share here. We are grateful for any advice before we "raise an alarm about 'nothing' " ;-) Can you do something yourself? Would a "heating device" solve the problem?

Your problem can be due to many causes. What is the construction year of the house? Is the basement built with masonry or concrete? How have the basement walls been sealed from the outside? An existing drainage system is already a good start. Are these collection shafts connected to the sewer or where do they drain? The described problem in the basement can be caused by backwater in the drainage, but then several factors would probably have to play a role. Assuming the basement is a black tank and during the installation of the backfill protection the studded membrane was installed without fleece with the studs facing the house, and the soil around it was mechanically compacted. This leads to damage to the thick bitumen coating and water could stand against the basement wall for a longer time in case of a backup in the drainage system and diffuse through the basement wall.
All just a hypothesis. You have to find the cause and, if necessary, give a nudge to the property management. The fan heater only treats the symptoms and that at your expense.

80% rel humidity at 12 degrees, that’s when mold really says hello! Speculation from the outside about the exact cause is actually not seriously possible. But based on experiences from recent years in my own cellar and those of acquaintances, I can say that most of the time it is moisture coming from the house that is not ventilated away sufficiently. This fits with:

- the rooms have no window, no light well or similar

So simple, so complicated: Of course you only ventilate when the outside temperature and humidity allow it (dew point). Otherwise you bring even more trouble into the house. But it is definitely no joy for the stored items; sooner or later they are ruined because of mold. I would first talk to the property management about a proper ventilation concept or maybe even suggest the installation of a dew point controlled ventilation system with heat recovery. But under the circumstances you described, enduring it is not an option.

Thank you very much for your feedback(!).

What year was it built? Is the basement made of masonry or concrete? How are the basement walls sealed from the outside? Are these collection shafts connected to the sewer, or where do they drain?

- the house is approximately built in 2000
- basement exterior walls and ceiling are made of concrete
- I cannot make any statement about the sealing of the house. (Isn’t a black tank standard at that time?)
- the shaft with the rungs might be connected to the sewer network. I cannot say for sure.
- (!) there is a terrace above the basement

But from experiences in recent years in my own basement and those of acquaintances, I can say that most of the time it is moisture coming from the house that is not adequately ventilated away. I would first talk to the property management about a proper ventilation concept or perhaps even suggest the installation of a dew point-controlled ventilation system with heat recovery. But under the circumstances you described, enduring it is not an option.

- The hallway is drier, and the smell does not occur there either. This is only the case in our room and one neighboring room. The problem has not occurred in at least three other rooms (but also on a different side of the house).

Further:
The property management will send someone to clean/flush the shafts.

We have now temporarily stored all items that quickly absorb the smell elsewhere. However, storage space is "scarce." My plan is to first put everything in writing and urge the property management to investigate this. Not by someone from the office inspecting, but by a professional. If nothing happens, I would wake up my landlord. I am also not familiar with our rights and what can be expected. I will read up on that and possibly seek help from the tenant association.

Can the "stains" be used to tell whether it is only moisture or already mold?

- the shaft with the rungs might be connected to the sewer network. I cannot say for sure.

There are more shafts. The property is 1500 m2 with two multi-family houses. Due to the decreasing bottom depth of the shafts towards the street, it is conceivable that they are connected. The one with the rungs is the one furthest away and the "shallowest."

Are you a tenant? Then contact your landlord, you have no legal right to commission anything yourself.

And honestly, basements without windows need a forced ventilation system.

Can one tell from the "spots" whether it is just moisture or already mold?