ᐅ KfW 70 with gas-solar heating system

Created on: 17 Apr 2015 21:01
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LittleWulf
Hello, we plan to start building our own home this year.

I already have two active discussion threads on this forum about it.

https://www.hausbau-forum.de/threads/Hausbau-kfw70-ca-150m-welche-Heizung-Gas-lwwp.12261/
https://www.hausbau-forum.de/threads/wir-wollen-bauen-ist-das-was-uns-angeboten-wird-so-i-o.12269/

We just got back from discussing the offer with the supplier.
I tried to talk about heating and ventilation; he shared his experiences, opinions, and advice.
This didn’t quite match what I had read so far, so now I’m uncertain and confused again.

We requested a 150m² (1,615 sq ft) solid house built to KFW 70 standard.

This is achieved through insulation and a gas-solar heating system. More details are in my other threads.

When I asked about a mechanical ventilation system with heat recovery, he said it’s not needed, that regular airing is sufficient.

He also said his son built a KFW 70 house with gas-solar three years ago and that he would never do that again. Better to build without KFW 70, save the money for the energy certificate inspection and the solar system (about 5,000), keep the insulation as is, and move on. Apparently, it’s not financially worthwhile.

Regarding the wall construction, another supplier told me the following:
Me: Is there an air gap between the insulation on the masonry and the facing brick?
He: Yes, of course, we don’t list that separately because it’s required by DIN (German industrial standards).

Today, with our current supplier:
Me: Is there an air gap between the insulation on the masonry and the facing brick?
He: No, that’s a cavity insulation. That might have been necessary in the past, but with today’s insulation materials, it’s no longer needed.

So what is correct? Is an air gap between the insulation and masonry required by DIN, or does it depend on which insulation material is used?
Mycraft18 Apr 2015 10:40
I have the opposite opinion... besides, there are still many houses that need insulation, or where the insulation must be renewed due to defects, etc... and here in Germany, timber frame construction will never really be able to compete with solid construction (also known as masonry or concrete construction)... at least that is the general feeling you can gather everywhere, and even on construction sites, at least in this area, you only see solid houses.
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Sebastian79
18 Apr 2015 10:43
What does the insulation of existing buildings have to do with new construction? Of course, there is a need for improvement, but that’s not relevant to the current discussion...? Nor are defects, etc.

And of course, you mostly see solid construction homes—please read carefully: This is an assumption on my part that this will be the next trend, eventually mandated by the government: ecological building, meaning the use of particularly sustainable materials. Because there will be no status quo, things always have to change and improve—but practically no improvements are left to be made when it comes to insulation.
Mycraft18 Apr 2015 10:48
What I meant is that the insulation will not stop but will continue, both in existing buildings and new construction...
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Legurit
18 Apr 2015 10:52
As far as I know, the goal is eventually to achieve zero-energy houses—whether off-grid or not, I am not sure. I strongly believe this can only be accomplished through a combination of insulation and energy generation.
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Sebastian79
18 Apr 2015 10:52
That’s your opinion, but regarding new constructions, I don’t see any economic or ecological potential there – as you asked: Have you really studied the insulation curve and calculated U-values?
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Legurit
18 Apr 2015 11:00
Lex, certainly not with 40cm (16 inches) of insulation, but whether it’s 14 or 18cm (5.5 or 7 inches), mineral wool can still make a difference...