Semi-detached house from 2010 - KFW40 without ventilation system

Hello!

In addition to our new construction plans, there is currently a very interesting semi-detached house for sale for us. 150 sqm, 5 years old, KFW40, generally very good equipment (oversized tiles and high-quality parquet, garage with sectional door, high-quality bathrooms, ..), however without a ventilation system (for whatever reason...).

Now my question: Kfw40 without a ventilation system.... do I have to expect problems? Should a decentralized variant be retrofitted or can one presumably live well without extreme ventilation effort?

As another note: Currently, only wood heating is used there (water-bearing fireplace connected to underfloor heating), but a gas boiler or air heat pump will be installed optionally (price-wise practically the same). Wall structure is 17.5 cm brick + 20 cm ETICS. Why I give this information: I guess that the KFW40 is mainly achieved through the wood heating, but I am too ignorant to assess this finally.

Many thanks in advance for answers!

HT is reached via the envelope, not via the heating - so it certainly isn’t complete nonsense. Also, the energy status does not necessarily have anything to do with air exchange. The fact that the box is KFW40 DESPITE the absence of a ventilation system is probably really due to the wood. Have them give you the energy saving ordinance and see how the calculations were done there. Just ask the residents what they say. From afar, I would estimate that you will need to ventilate well. Decentralized controlled residential ventilation can of course be retrofitted - how good or complex it is, I would check in advance - so that you don’t damage any installation layers or otherwise have to seal something.

For the year 2010, the most difficult ventilation period is over, the construction moisture is out.

I think it doesn't matter which KFWxx it is, without a ventilation system you just have to ventilate.

I live in a semi-detached house from 2011, without [Kontrollierte-Wohnraumlüftung], two working people. I don't see any mold anywhere...

But I would like to have ventilation in the bathroom...

Thank you very much for the answers. I made an inquiry regarding heating load, [Energieeinsparverordnung]-calculation, [Energieausweis] and building description and received a direct response.

I will only receive the [Energieeinsparverordnung] and [Energieausweis] next week, as they are located elsewhere. However, I was already informed that the new heating system with 6 kW will be absolutely sufficient. 6 kW for just under 150 sqm, that should be enough for a rough assessment regarding the energy standard of the house, right?!

What seems strange to me: Apparently, there is no building description, just as there is no development plan. Can it really be that there is no building description for a house from 2010? At least for the approval, it is absolutely necessary, and you wouldn't just throw something like that away, would you? I am skeptical, rightfully so?

Depends on how it was built - if by individual contract it doesn't necessarily have to exist. To my knowledge, there doesn't necessarily have to be a development plan either - but then they should be able to tell you what was commissioned where. You're concerned about the ventilation, not the energy, right? A plastic bag definitely has pretty lousy insulation but you still die of lack of oxygen after 4 minutes.

Have all construction documents handed over to you for review. I find it strange that there are no specific documents for a 2010 KFW house.

Why is the house being sold again after such a short time?