ᐅ Semi-detached house from 2010 – Built to KfW 40 energy standard without a ventilation system

Hello!

In addition to our new construction plans, there is currently a semi-detached house for sale that is very interesting to us. It’s 150 sqm (1,615 sq ft), 5 years old, KfW 40 standard, with generally very good features (extra-large tiles and high-quality parquet flooring, garage with sectional door, high-end bathrooms, etc.), but without a ventilation system (for whatever reason...).

Now my question: KfW 40 without a ventilation system... should I expect any issues? Would it be advisable to retrofit a decentralized system, or is it likely possible to live comfortably without significant ventilation effort?

As an additional note: currently, it is heated exclusively with wood (a water-bearing fireplace connected to underfloor heating), but either a gas boiler or an air source heat pump will be installed soon (both roughly the same price). The wall construction consists of 17.5 cm (7 inches) brick plus 20 cm (8 inches) external thermal insulation composite system (ETICS). The reason I mention this is that I assume the KfW 40 standard is mainly achieved through the wood heating, but I lack the knowledge to assess this definitively.

Many thanks in advance for your answers!

HT is achieved through the building envelope, not through the heating system—so it’s definitely not complete nonsense. Also, the energy rating does not necessarily have anything to do with air exchange.

The fact that the structure qualifies as KfW40 even without a ventilation system is probably due to the wood construction. You should get a copy of the energy saving regulations and check how the calculations were done there.

Try asking the occupants what they say about it. From a distance, I would estimate that you will need to ventilate well. Decentralized controlled residential ventilation can certainly be retrofitted—how well or how complex it would be, I would advise checking in advance—not to risk damaging any installation layers or having to seal anything unexpectedly.

For a building from 2010, the most challenging period for moisture from construction is over.

I think it doesn't matter which KFW standard it is—without a ventilation system, you simply have to ventilate manually.

I live in a semi-detached house from 2011, without a mechanical ventilation system, and both of us work full-time. I don’t see any mold anywhere...

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

Thank you for the responses. I submitted a request regarding heating load, energy saving regulation calculations, energy certificate, and building specifications, and I received a direct reply.

The energy saving regulation documents and energy certificate will only be available next week because they are stored 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 (1615 sq ft) should be enough for a rough estimate regarding the energy standard of the house, right?

What seems odd to me: Apparently, there is no building specification, and neither is there a development plan. Is it really possible that there is no building specification for a house built in 2010? At least for the building permit / planning permission, this should be mandatory, and such documents are not simply discarded, are they? I am skeptical—rightly so?

It depends on how it was built – if it was done through individual contracts, this might not be necessary. As far as I know, a building plan or zoning permit doesn’t always have to exist – but in that case, they should at least be able to tell you who was hired for which parts.

You’re asking about the ventilation, not the energy efficiency, correct? A plastic bag definitely has very poor insulation, but you would still suffocate after about 4 minutes due to lack of oxygen.

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

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