ᐅ Basement ventilation system without windows

Hello everyone,

Our ventilation system has finally been up and running since the weekend.

The air quality in all rooms is noticeably much better than before. So far, I’m really impressed!

Our ventilation installer mentioned that it’s possible to program the current setting from “1” to “2” during the day and then have it automatically switch back to setting “1” at night to keep the noise level low.

At the moment, I don’t find the air quality bad and don’t see a reason to increase the setting (but this shouldn’t cause any disadvantages, just stronger ventilation, right?). In my opinion, setting “2” is hardly audible either!

Do you usually ventilate bathrooms manually with windows after showering when you have a ventilation system, or can/should I generally avoid manual ventilation?

Our basement currently has a constant humidity level of 70%. We have no windows there since it’s purely a utility basement. The ventilation system is connected in this area as well.

A few weeks ago, we had serious mold problems because we stored a lot in the basement and the ventilation system wasn’t running yet.

Now my question:

Do I no longer need to worry about mold as long as the system is operating? Can mold develop even with continuous ventilation? I probably won’t be able to lower the 70% humidity quickly since we have a waterproof (WU) basement and it’s a new build that needs time to properly dry out.

Is drying laundry an issue at this stage? We have a separate laundry room in the basement that is also ventilated by the system.

Or:

Should I generally wait a few more months before using the basement as a storage space?

I look forward to your feedback 🙂

I think you should take a step back and focus on professional building drying. How else do you plan to keep the basement dry?

And yes, ventilation!

guckuck2 schrieb:

I think you should take a step back and focus on professional building drying. How else do you plan to get the basement dry?

And yes, ventilate!

We already had a drying phase of 3 weeks due to a small water damage, using various drying devices and so on.

As a result, we managed to reduce the humidity from the original 95% to 70% relative humidity.

A professional building drying service is probably no longer necessary…

I also consider 70% to be relatively uncritical when our ventilation system is running – although I could be wrong, which is why I started this thread.

Because of today’s fast construction pace and the fact that everyone wants to move in quickly, the humidity is certainly very high at the beginning.

Our basement now also feels “pretty” dry. Running the ventilation system makes me feel a bit more confident.

However, this doesn’t really answer my question about how to handle laundry drying or storage of various boxes or cartons and the like.

Otherwise:

Does it make more sense to keep the individual basement rooms closed or should I leave all doors open for the first weeks or months so that the air can circulate better? We have an open stairwell leading to the basement.

Or: Does this interfere with the proper design/planning of the ventilation system per room?

Prager91 schrieb:

However, this doesn’t really answer my question about how to handle drying laundry or storing various boxes/cartons, etc.

Yes, it does. My statement currently rejects any use of the basement until it has been properly dried.
We are talking about a utility basement (possibly even unheated) with no windows at all. The ventilation is not running yet either.
The logical consequence, even at 70% humidity, is mold. Guaranteed. If not on large surfaces, then behind or inside items placed tightly against the walls, for example. Cardboard boxes placed directly on the floor are a prime example; you can forget about the documents or clothes inside them. Anything that is not ventilated (which in an unventilated, damp basement is a relative term) is at risk.

Prager91 schrieb:

Or: Does that interfere with the correct design/planning of the ventilation system per room?

No. Standard mechanical ventilation systems with heat recovery operate on the principle of overflow ventilation; that means one room has supply air, one room exhaust air, and the area between them is the overflow zone (hallway). This way, all three rooms mentioned are ventilated.
This requires open doors or closed doors that still allow airflow, usually via the gap under the door or via specific overflow elements in the door frame.

Prager91 schrieb:

Does it make more sense to keep the individual rooms in the basement closed, or should I leave all doors open for the first weeks or months to allow better air circulation? We have an open stairwell to the basement.

You MUST continuously and thoroughly VENTILATE this basement, preferably also DRY it additionally or HEAT it.

At grandma’s place, mold first appears behind the wardrobe against the cold wall. Apply the same principle here.

guckuck2 schrieb:

No. My statement currently rejects using the basement until it has been dried.

We are talking about a utility basement (possibly unheated?) that has no windows. The ventilation is also not yet operational.
The logical consequence, even at 70% humidity, is mold. Guaranteed. If not on large surfaces, then behind or inside objects placed close to the wall, for example. Cardboard boxes directly on the floor are especially susceptible; you can write off any documents or clothing inside them. Anything that is not ventilated (which in an unventilated, damp basement is quite likely)

No. Standard mechanical ventilation systems for living spaces work on the principle of air transfer, meaning one room has supply air, another has exhaust air, and between them is the transfer area (hallway). This way, all three rooms mentioned are ventilated.
This requires open doors or closed doors that still allow air transfer, usually through the gap under the door or via dedicated transfer elements in the frame.

You MUST continuously and thoroughly VENTILATE this basement, ideally also DRY and HEAT it.

At grandma’s house, the first place mold grows is behind the wardrobe on the cold wall. Apply this principle.

I’m not sure if you might have missed my post, but our ventilation system is now operational! Also, as already mentioned, we performed drying of the basement for 3 weeks.

Before that, during the shell construction phase, the screed was already dried for several weeks.

I definitely cannot and do not want to dry any more – for now, I prefer to wait and let the basement dry out naturally.

The basement is unheated, but all rooms are connected to the ventilation system and are therefore continuously ventilated.

So:

Should I simply wait before storing anything, or is it possible to store now? As I said, the system is running! 70% humidity in the basement is certainly not particularly bad – the trend is actually decreasing at the moment.

Prager91 schrieb:

I don’t know if you maybe didn’t read my post properly, but our ventilation system is now up and running!

That wasn’t entirely clear to me.
Are the 70% humidity values from before or after the ventilation started? What is the current humidity at what temperature?

Prager91 schrieb:

Also, as already mentioned, we carried out drying of the basement for 3 weeks.

Before that, during the shell construction phase, the screed was already drying for several weeks.

That’s all fine and well, but who cares? What matters is the current condition, and in my opinion, it’s still not good.

Prager91 schrieb:

I definitely don’t want to dry out any longer – I will wait and let the basement “dry out” on its own.

You should be aware that in a concrete basement with insulation on the outside, without heating, nothing really dries. The only effective method is a controlled mechanical ventilation system to ensure air exchange and circulation. You depend on that. Unfortunately, you’re rejecting other measures. This type of drying will naturally take time.

Prager91 schrieb:

70% humidity in the basement isn’t especially bad – the trend is currently going down.

If the controlled mechanical ventilation is running and the trend doesn’t improve significantly, you clearly have a problem.

70% is better than 90%, but that’s about it.