KfW 55 - Ventilation system yes/no? - Experiences

For that, I have a humidifier placed in an exhaust room, which then humidifies the air, and the system distributes it throughout the house via the enthalpy heat exchanger.

But that only really works with an enthalpy heat exchanger, right? Otherwise, in a typical controlled residential ventilation system, there is no place where air exchange of exhaust/supply air would take place, correct?

I had a similar conversation with a general contractor. The whole argument collapsed the moment I read the contract – the same "works great without controlled residential ventilation" contractor exempted himself from all moisture damage and required the homeowner to ventilate multiple times a day. That’s not consistent either. I was allowed to inspect an occupied KfW55 house without controlled residential ventilation, where no ventilation had been done beforehand – my first impression was: rather stuffy here.

Same here. The general contractor prefers to install decentralized ventilation, and in all the contractor’s houses we visited, the systems were turned off and the air was really stuffy. So decentralized or no ventilation was immediately ruled out for us.

Just had 2 new conversations with 2 other GU --> So a total of 3 different conversations with GUs. The GUs nearby build almost everything in the surrounding new development areas and all have a very good reputation.

All, really all, told me that KFW 55 + without ventilation is no problem. You just have to ventilate normally and then it’s fine. They all also said that it depends on the building material, and if you use bricks, you won’t have any problems because of the diffusion openness. Moisture release is therefore not a problem and they have all never had any issues with mold so far. KFW 70 is pretty similar to KFW 55, they all said. In principle, they would all also build KFW 70, but it makes little sense due to the subsidies.

If a ventilation system is used, they are all of the opinion to install it decentralized. Regarding central ventilation, they all mentioned the same problem: The pipes look filthy and you don’t really want to look inside.. What might be inside after a few years is also not really clear yet.

Yeah, then "everyone, really everyone" has no clue...
Diffusion-open bricks - oh, another one talking about breathing walls?
Decentralized LA - that really brings joy.

The pipes look like crap? a) How do they want to know that? b) Nothing happens after a few years - except maybe if you don't install filters. By the way, you can also clean those things.

No one can ventilate properly unless they are home all day, don’t sleep through the night, and have a fetish for opening windows.

The cheap alternative is window rebate vents with a central exhaust. At least they ensure some air exchange.

These seem to be GUs who build as they have always built, so the regulars' table slogans about ventilation systems fit well into the picture. For me, all three would be out, at most I would have them carry out gas + ST. Under no circumstances, however, a heat pump or (decentralized) ventilation system.

This is really amazing...

Is it possible for me to look for a tradesman who installs the ventilation system? Can this be installed parallel to the house construction or can it (central system) also be installed later, or do I have to coordinate this accordingly with my general contractor?

Maybe I'll look for someone myself who does this properly and leave the general contractor out of it...

Honestly, I won’t find a general contractor here who "likes" to install these ventilation systems.

Presumably, it’s because this KfW 55 business is very, very new and the general contractors haven’t thought about it yet.

I just find it very difficult: They all build around 120 houses a year, all KfW 70, and apparently no one had problems with or "missed" this ventilation system. I don’t think a KfW 55 house differs that much from a KfW 70 house.

On the weekend I’ll visit my cousin who built a KfW 70 house without a ventilation system. The blower door test showed that it is very, very close to a KfW 55 house. So I can also find out firsthand what’s going on here.

Yeah, so then "everyone, really everyone" has no clue...
Diffusion-open bricks - so, someone else talking about breathable walls?
Decentralized ventilation - now that really brings joy.

The pipes look like hell? a) How do they want to know that? b) Nothing is there after a few years - except maybe if you don’t install filters. By the way, you can also clean those things...

No one can ventilate properly unless they are at home all day, don’t sleep through the night, and have a fetish for opening windows.

The cheap alternative is window rebate ventilators with central exhaust. They at least ensure some air exchange.

So, is the building material not decisive for the indoor climate, or can a certain building material not prevent mold?