Diffusion-open wall construction - I don't get it!

For a house provider, special emphasis is placed on the diffusion-open wall construction in the house description. This is also one of the main reasons why the provider does not install a central ventilation system. Another reason is that biomass (smaller dust particles, etc. in the air) is attracted in the pipe system, and contamination (mold formation) can occur quite quickly in the distribution system.

Now I have two problems with this.

1. We tended to want a ventilation system, and the provider generally does not install one.
2. We now do not know how great this diffusion-open wall construction is and whether it might be sensible to do without the ventilation system because of it.

Here is briefly the wall construction (Swedish house facade) from inside to outside:

15 mm high-quality Fermacell solid construction panels
40 mm wooden frame construction with Knauf Insulation 40 mm WLG 040
0.2 mm vapor retarder SD 100 m
160 mm wooden frame construction with Knauf Insulation 160 mm WLG 040
30 mm wood fiber insulation board
24 mm battens
Approx. 20 mm SL cladding, spruce (color according to color chart)

It would be very nice if someone could explain to me the advantage of this diffusion-open wall construction compared to other walls with wooden stud construction. Especially the relation to the ventilation system would also be important to us. With Hagemann Haus, we would have to do without this ventilation system after all.

Hello,

At Hagemann Haus, we would at least have to do without this ventilation system.

I know this provider from the documents that a user of this forum made available to me.

The managing director is basically against ventilation systems and uses outdated arguments that no longer apply to today’s systems; in return, his offers are quite affordable, considering that his company is not that big.

These days, I would no longer want to do without a ventilation system, let alone have to; neither in solid construction, especially not in conventional prefabricated house construction, and also not in a wooden house. It is therefore up to you whether you follow the provider’s arguments or look for other suitable options. Any discussion or evaluation of the wall structure is pointless here if this provider is an absolute must.

Best regards from the Rhineland

..... but his offers are quite inexpensive, considering that his company is not that big.

Rhenish greetings

However, the price is exactly an argument that makes the supplier attractive to us. That is the difficulty....

The matter of diffusion-open construction should be approached with caution. Theoretically, this wall structure may be diffusion-open, but in practice, it can also go wrong, because houses must primarily be airtight according to the Energy Saving Ordinance. The question then is whether the moisture can be transported outside in the necessary time and volume without it starting to mold somewhere.

If the installation of a ventilation system is then categorically excluded, that would be enough for me to look for another provider.

By the way, there are wall structures that are diffusion-open and can also do without a vapor barrier foil. OSB boards, if properly dimensioned and positioned, also act as a vapor barrier and you do not have to worry that the foil will eventually be eaten away by rodents or destroyed for other reasons.

But even in that case, I would definitely not want to do without a ventilation system.
A ventilation system is simply part of modern living today. There are opponents who also have their good reasons, but personally, I consider it a great gain in comfort and a sensible contribution to the preservation of the building fabric.

Hello,

Especially the price is an argument that makes the provider attractive to us. That is the difficulty....

I don’t see it -

if you want to choose this provider, then take their offer as it is. If you can’t, look for an alternative. There is zero room for negotiation, as the GF – as stated above – will not be persuaded on this point.

Foolish greetings

I doubt that there is a wall structure that complies with the energy saving regulation AND allows enough moisture to diffuse outward so that ventilation can be omitted. Moisture escapes outside through ventilation. The walls have no noticeable lasting effect (of course, certain wall structures/surfaces can temporarily absorb peaks).