Is controlled residential ventilation necessary with expanded clay and KFW55?

Dear forum community,

after we have now found a plot of land, it is time to specify the technical building equipment.
We want to have a KFW55 house with a heat pump built. So far so good. After diligently reading the forum, I was actually sure that we also need a central controlled residential ventilation system (we are at the office all day and will probably not be able to carry out the necessary shock ventilations for air and humidity exchange).

Our builder believes that a central controlled residential ventilation system is not necessary with his construction method due to the use of lightweight expanded clay aggregate. In addition, he installs a Regel-Air system in the windows. A controlled residential ventilation system is installed by him - if at all - once a year. With over 100 houses per year. In his opinion, the situation would be completely different with Ytong. There, a controlled residential ventilation system is always necessary.

If we still insist on a controlled residential ventilation system, the additional costs are about 15,000€ for the device (Pluggit) and 8,000€ for raising the walls on the upper floor and the screed on the upper floor. So a total of 23,000€. According to the reports here in the forum, I consider the surcharge very high.

Our builder builds with lightweight expanded clay aggregate. The wall structure is roughly:
- 15cm lightweight expanded clay aggregate
- 19cm insulation
- vapor barrier and exterior plaster
Total wall structure: approx. 35cm

I cannot assess the builder’s statements. Do you really not need a controlled residential ventilation system with lightweight expanded clay aggregate because the properties regarding humidity are so good?
I would be very grateful for your help.

Best regards
Matthias

With us, the controlled residential ventilation from Bosch (ground-water heat pump is also from Bosch) costs an additional €12,000 to a maximum of €13,000. However, we build in monolithic construction, a bungalow, 3m ceiling height excluding FHB.

Our general contractor initially also said that controlled residential ventilation was not necessary. After a long back and forth, we decided in favor of it.

Just take a moment to think about what the developer is saying there. And dismiss the whole story as complete nonsense. Of course, it's nonsense; what role should the masonry play in that? However, if you plan a pink toilet bowl, then the controlled residential ventilation can probably be omitted.

Just take a moment to think about what the developer is saying there. And dismiss the whole story as complete nonsense. Of course, nonsense, what role should the masonry play there. However, if you plan a pink toilet bowl, then the controlled residential ventilation can probably be omitted.

What? Have you never heard of breathable walls? :cool:

The statement regarding the wall construction is certainly nonsense overall.

His conclusion that the central controlled residential ventilation in his houses is unnecessary is surely not based on the wall construction, but on the installed "Regel-Air-System." Whatever that may be in detail.

The developer obviously cannot offer/implement a controlled residential ventilation system at a reasonable price with his construction method and therefore advises against it. At least, that will be the reason why only one out of a hundred of his builders installs the controlled residential ventilation. Nothing else.

Our developer builds with expanded clay. The wall structure is roughly:
- 15cm expanded clay
- 19cm insulation

I would rather put it like this: "builds ETICS using an expanded clay load-bearing shell". But to your actual question: I can only agree with , it hardly gets more nonsensical than that. has window ventilators and monolithic aerated concrete; I don't see the difference "boiler instead of heat pump" as relevant for controlled residential ventilation. What I find crucial is your self-assessment that you cannot ensure regular ventilation in everyday life. Then you need one of the two systems that take that off your hands - and in my opinion, it's your personal "religious" conviction whether it should be window ventilators or controlled residential ventilation. You apparently need to take your builder's technical opinions with a grain of salt; this usually applies equally in all areas.