ᐅ Which wall assembly is suitable for being vapor-permeable?

Hello everyone,

I am currently researching wall construction with a focus on vapor-open systems. I am very concerned about mold growth in the house, which is why I have often read that a vapor-open build is preferable (using a vapor retarder instead of a vapor barrier). However, when I look at the wall constructions of various manufacturers, a vapor barrier is often installed rather than a retarder (for example, Danwood). If the mechanical ventilation system fails, does this then inevitably lead to mold growth? Can anyone share their experience with how this (PE foil) actually performs in a house? Are there wall constructions where a mechanical ventilation system is installed as a nice-to-have but not essential? We currently live in an apartment and have to air the rooms multiple times in winter to prevent mold from forming under the blinds’ boxes. Are there houses or walls that do not experience these problems? We definitely want a ventilation system, but I would like to avoid the worry of mold growth within a few days if the system fails.

Thank you very much for your experiences.

No experiments.
Keep it classic. No vapor barrier, no expanded polystyrene (EPS) insulation. Use 36.5cm (14.4 inches) Ytong blocks, plastered inside and outside, done. We live without mechanical ventilation, only with window frame vents and an exhaust fan (Helios) in the bathroom. No mold anywhere. Please do not enclose it in plastic sheeting.

Ok, thanks. Yes, that's my concern. Did you build independently or with a company?

No matter what type of house you build. They are ALL airtight and have the same issues if you don’t ventilate. Timber frame construction with vapor barriers, monolithic walls, or with external thermal insulation composite systems (ETICS) makes no difference.

@Nordlys manages thanks to continuous ventilation through window frame vents. This is an uncontrolled residential ventilation system (URVS).

New houses = ventilation is important

Regarding the question: With a general contractor. Everything from a single source.

Hausbauer2021 schrieb:

We definitely want to have a ventilation system, but I don’t want to be worried about mold developing in the house within a few days if the system fails 🙁

Firstly, there is no reason why the ventilation system should fail, and secondly, mold does not form immediately.
If, in the unlikely event, there is a power outage for 3 or even 13 days (which seems quite unbelievable), you can still ventilate manually. The important factor is not the device itself, but the air exchange.
And yes: modern houses are practically airtight. That is why they stay nice and warm.