Insulation or not?

Hello everyone,

Yesterday I went with my husband for construction advice at a well-known construction company.
Our idea: we want to build a bungalow according to Kfw70 with about 120m² of living space with gas and solar.

Now this salesperson said that KfW70 is not worth it at all. The additional insulation saves about €85 per year on heating costs but costs €8,000-9,000 more to purchase. He recommended a 30 cm exterior wall made of aerated concrete. That would be enough; additional insulation is not necessary.

Now we are a bit confused. Is he right? Or did he just want to make the numbers look better so that the total sum stays low.

Does that make sense? How did you do it? Is extra insulation worth it or can you do without it with an appropriate exterior wall?

Looking forward to your opinions.

hm, I'll answer quite cheekily as a layman: I personally don't trust anyone who wants to calculate my energy consumption. It's just like fuel consumption in a car: every car I've ever bought in my life consumed more per 100 km than the manufacturer's specifications. About 20% more, actually. At first, I also thought a house built to the Energy Saving Ordinance 2009 standard would be enough. A 15% saving isn't much... nowadays, but who knows what it will look like in 10 years? Then 15% of factor x could be a lot. Also not to be underestimated: the Kfw70 loan. We save 1.5% of 50,000 €, which is already 7,500 over 10 years :) And keep in mind: you can't just upgrade thermal insulation anytime you want! A bigger financial leap would be Kfw55 or a Passive House; there I would think it over, weigh it up, and consider today's realities and today's wallet. But just wait for the answers from the calculation wizards and experts :)

yes we have also already calculated that the effort would pay off again through the interest savings. But it is really strange why so many people still build without insulation. Aren't all these Kfw things useful???

I don't know anyone now who doesn't insulate additionally. Stones also provide insulation. The tendency among young people is rather towards passive houses, but whether that is economical is questionable :rolleyes: You also have to consider resale value. I currently live in a house from 1978, my parents also built in 1978, insulated only with air. If it weren't for the insane costs of additional insulation for used properties, I probably would have bought one like this again instead of building new. It doesn't pay off. I think the future belongs to technology, not the building envelope, because eventually, you can't insulate anymore. So, wrap the house well and plan it to be upgradeable for the future :)

Yes, this is all very confusing. We also thought that being at KfW70 put us in a good position. He just said that it is sufficient to build according to the valid Energy Saving Ordinance. The savings you get from KfW70 are simply not worth all the effort. We will not be working with this construction company, that is already certain. And KfW70 remains our goal, as we still belong to the younger generation and the house should last for a while here.

Best regards