KfW 55 - Ventilation system yes/no? - Experiences

I just find it very difficult: They all build about 120 houses a year together, all KfW 70, and apparently none of them had problems with it, or "miss" this ventilation system

They don't have to live in them either, or surely window rebate ventilators are installed. And regarding the residents: what you don't know, you don't miss. I always experience it with my parents-in-law: house from 2013, well sealed without any form of ventilation. When we sit there in the living room with the children and sometimes uncle/aunt, 8 in total, after half an hour you start getting suffocation anxiety – then every 30 minutes all the windows and doors are thrown open because half the group is just about to fall asleep. Then you get a cold shock, wake up again, only to start dozing off slowly again with the windows closed. KfW plays no role here at all, but 90% depends on how good and tight the windows and doors are. My wife always has headaches after such a day – but that may also have other reasons ..

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

A building material is certainly relevant for the indoor climate, but in the end, the interaction is decisive. The statement "I build with Poroton bricks, it can't mold" is simply wrong.

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

Of course, an external company can also install the ventilation system. However, the schedules must be coordinated very precisely. The ducts for the ventilation system are usually located on the raw subfloor, meaning they come before the underfloor heating and the subsequent screed. Therefore, the installation date must fit perfectly. Something like this cannot be installed afterwards.

In the past, people had cars with crank windows and phones with cords, etc., and no one missed anything or had "problems with it." You just simply went to the phone booth on the corner.

What you don't know, you don't miss.

The problem with house construction is... due to the modern and basically intentional building style, houses are built so tight that no natural air exchange can take place (unlike the houses of parents and grandparents). In other words, nowadays you need some kind of forced ventilation if you want to have "fresh air" in the house. Because, as Lumpi wrote, no one can stick to the ventilation intervals. Another tricky part of the matter is that hardly anyone changes their ventilation behavior and they continue to ventilate as they did in the rental apartment before building the house.

You notice this quickly when you set up a measuring device.

Of course, people always claim they ventilate properly and sufficiently, and even the general contractors say: "You don’t have to do anything except ventilate." They usually don’t know it any other way. As long as there is no change of mindset, building will continue as before. Why would you change, you’ve always done it that way.

The statement about dirty pipes is simply the height of ignorance. Certainly, the pipes get dirty over time, but these are usually the exhaust air pipes. Experience shows that even after 10 years, the ventilation pipes for the supply air look like new. It’s no wonder, after all, only fresh and filtered air comes in. Dirt has no place there. Provided, of course, that you don’t live in the immediate vicinity of a coal mine and replace the filters according to the manufacturer’s guidelines or when the system indicates a full filter.

I also find all of this really plausible...

I just don't understand how this way of thinking can still prevail nowadays...

It's probably because all the building owners don't give it a second thought and just do what the general contractor says. I'm going to make an appointment with a ventilation installer nearby and listen to his opinion on this. Then I can confront the general contractor with it.

The problem is simply that my entire perception of the different general contractors has now completely changed.

Have you already been in a new building according to the Energy Saving Ordinance 2016 or KfW55?

The GUs usually do what is simple and not prone to errors. They also don't want to bother with you afterwards. Hole in the wall and blower in, is mega easy.

Of course, you can also live well in the new houses without ventilation and I haven't seen mold in the houses either. But it is better and the air quality is noticeably and also tangibly better with controlled residential ventilation.

I just don't understand how this way of thinking can still prevail nowadays...

Because something like this takes decades. Most people still think nowadays that heat pumps are something new and groundbreaking.