Does mold go away by insulation or not?

When we modernized the windows in our house (also triple-glazed), we were warned that there could be problems with mold. So far (a few years) there has been no sign of it – what I have remembered is that for the mold problem it is unfavorable if the insulation in the house is too uneven.

In an existing building, one probably retrofits with a decentralized solution.

It depends on the house. Genuine old buildings often have disused chimneys (because nowadays not every room needs a stove anymore). These can be used for the central ventilation system. Together with high rooms that can have lowered ceilings, that can fit well. We are currently having this planned for our house, and the planner has already given his general approval...

Real old buildings

… are unfortunately rare. The usual "old building" from 1950-1980 does not qualify.
I would also prefer central over decentralized.

Hello dear ones,

first of all, I wish you a happy New Year! Lots of health, success, and above all no problems with your property :-)

Thank you very much for all your previous answers – they were really informative and helpful.

Today we looked behind the cupboards that stand against an exterior wall. It was a disaster!

There was so much mold behind the cupboards – I have never seen so much!

I have read that cupboards should not stand too close to the exterior wall so that air can circulate.

Today, we first sprayed all affected spots on the walls with mold remover, opened all the windows, and left the house for three hours.

It is so bad that I actually don't want to live here anymore. But my husband says that with insulation everything will get better.

I am really more desperate than ever before!

I measured the temperatures on the exterior walls with a laser: In the corners they drop to 11–16 °C, in the middle of the walls they are about 16–20 °C. Interior walls and the ceiling mostly have 22 °C.

We have a measuring device that displays the humidity and room temperature. Generally, the temperature in the bedroom, kitchen, etc. is around 21 °C and the humidity is between 60–75 %.
I know that more ventilation would help, but should I ventilate every hour now? Then it will never get warm in the house, and we will heat unnecessarily.

It feels like a vicious circle: Either cold and no mold or warmth and mold.

As I said, I am really desperate, and the mold discovered today makes it even worse.

I don't even want to look behind the kitchen cupboards (whether standing or hanging cupboards). It will probably look the same as behind the wardrobes.

My husband says that we will insulate the house from the outside this summer and then wait to see if the mold returns. If it does, a ventilation concept would be needed – probably with decentralized ventilation systems.
I have already watched some videos on YouTube about this. If the mold does not return, we would initially do without the ventilation systems, since they are not exactly cheap either.

My question: Do decentralized fans need to be installed in every room, or are they sufficient in the kitchen and bathroom?
Does anyone have experience with this? Can someone recommend good and preferably inexpensive fans? Which versions make sense?

Sorry for the long text, but I had to get all this off my chest and hope for helpful tips and a solution.

I wish you all a nice weekend!

Best regards
Julia

There was so much mold behind the cabinets – I have never seen that much before!

I read that cabinets should not be placed too close to the exterior wall so that air can circulate.

Exactly. The wall is cold (like the outside corners) and no air reaches it if the cabinet is right up against it.

But my husband says that with insulation everything will get better.

Men are always right. In this case, really, because the exterior wall will then be warm from the inside as well and water can no longer condense.

I measured the temperatures on the exterior walls with a laser: in the corners it drops down to 11–16 °C, in the middle of the walls it is about 16–20 °C. Interior walls and the ceiling usually have 22 °C.

the humidity at 60–75 %.

At 21 degrees and 60% humidity, the dew point is just under 13 degrees. So the room corner behaves like the cola you take out of the fridge in high summer. At 75% humidity even at 16.5 degrees. Unfortunately, physics wins here.

My husband says that we will insulate the house from the outside this summer and then wait to see if the mold returns. If it does, a ventilation concept would be needed – probably with decentralized ventilation systems.

Yes, then there is a very high probability that there will be no more mold, because the walls will then also be at 19–20 degrees.
BUT: Create the ventilation concept today. And also start thinking about decentralized fans today. You should install them before the insulation, as core drilling to the outside will be required. If no power cables should go into the walls, the fans can also be operated with power cables/outlets.
At least do it so that you have a certain basic ventilation.
Many manufacturers also plan something like that.

since they are not exactly cheap either.

For €400 each plus installation (which you can also do yourself) you can get good devices. Well-spent money.

My question: Do decentralized fans have to be installed in every room, or are they sufficient in the kitchen and bathroom?
Does anyone have experience with this? Can anyone recommend good and reasonably priced fans? Which types make sense?

Good question. Ideally, the air exchange required by the ventilation concept should also be achieved. Much more important than the kitchen, for example, I find the bedroom – that's where you produce the most humidity at night in the whole house.
Post your floor plan.
And yes, I have experience with central ventilation (in new buildings) and decentralized ventilation (currently in a renovated old building). Fans only with heat recovery, please. They are a) controllable together (cable) b) night mode (lowest power when dark because of noise) c) with humidity sensor (especially good in the bathroom). The cheap devices are pendulum fans – e.g., 70 seconds air out, then reversed. There are more expensive devices with cross-flow heat exchangers that blow in and out continuously and are also quieter.
In my case, the devices run almost continuously on basic ventilation. Then you don't hear them during the day and only very lightly at night in bed (but not disturbing).
Feel free to ask.

...and please also ventilate properly and thoroughly. 21 degrees and 60-75% relative humidity indicate incorrect ventilation. Expect that it will take you several weeks/months to reach acceptable values, as (simply put) all materials have absorbed water that first needs to be ventilated out...