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?
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?
Exterior masonry according to KfW 85 standard:
- 17.5cm (7 inches) aerated concrete
- Mineral fiber insulation mat with a minimum thickness of 14cm (5.5 inches) as per thermal insulation verification (thermal conductivity 0.035 W/mK)
- 11.5cm (4.5 inches) facing brick
For an additional cost of €2,000, the following upgrades are available:
- 140mm (5.5 inches) cavity insulation with a thermal conductivity of 0.035 W/mK in the facing masonry
- 180mm (7 inches) mineral wool insulation with a thermal conductivity of 0.035 W/mK in the rafter area
- 240mm (9.5 inches) mineral wool insulation with a thermal conductivity of 0.035 W/mK in the collar beam area
- 100mm (4 inches) polystyrene rigid foam insulation with a thermal conductivity of 0.035 W/mK under the ground floor screed
In addition, there is the solar system for domestic hot water preparation.
This would make the KfW 70 standard achievable.
The expert appraisal will, of course, cost about €500 extra.
- 17.5cm (7 inches) aerated concrete
- Mineral fiber insulation mat with a minimum thickness of 14cm (5.5 inches) as per thermal insulation verification (thermal conductivity 0.035 W/mK)
- 11.5cm (4.5 inches) facing brick
For an additional cost of €2,000, the following upgrades are available:
- 140mm (5.5 inches) cavity insulation with a thermal conductivity of 0.035 W/mK in the facing masonry
- 180mm (7 inches) mineral wool insulation with a thermal conductivity of 0.035 W/mK in the rafter area
- 240mm (9.5 inches) mineral wool insulation with a thermal conductivity of 0.035 W/mK in the collar beam area
- 100mm (4 inches) polystyrene rigid foam insulation with a thermal conductivity of 0.035 W/mK under the ground floor screed
In addition, there is the solar system for domestic hot water preparation.
This would make the KfW 70 standard achievable.
The expert appraisal will, of course, cost about €500 extra.
For us, the KfW70 standard will cost an additional 7,000 EUR. In return, we will get thicker and better insulation.
I actually thought that with the following features, the KfW70 standard would already be met. We have:
- 24.5 cm Poroton blocks + 12 cm VMS (insulation) + 2 cm external plaster
- Triple-glazed windows
- Solar system for domestic hot water preparation including a 300-liter (79-gallon) storage tank
What would need to be different to achieve KfW70?
For 7,000 EUR, it probably doesn’t make much sense, does it!?
I actually thought that with the following features, the KfW70 standard would already be met. We have:
- 24.5 cm Poroton blocks + 12 cm VMS (insulation) + 2 cm external plaster
- Triple-glazed windows
- Solar system for domestic hot water preparation including a 300-liter (79-gallon) storage tank
What would need to be different to achieve KfW70?
For 7,000 EUR, it probably doesn’t make much sense, does it!?
I also find that very strange. All I was told is: "For KfW 70, your house will have additional insulation." Unfortunately, I have not (yet) received any information on what the insulation would look like.
Solar thermal is definitely already included as standard and does not cost extra.
Solar thermal is definitely already included as standard and does not cost extra.
D
Doc.Schnaggls24 Apr 2015 14:04fischman schrieb:
Solar thermal systems are definitely already included as standard and do not cost extra.Hello,
solar thermal is probably already included because since 2009, a certain portion of the building’s energy demand must be covered by renewable energy sources.
That is why most buildings heated by gas now have these solar thermal collectors (usually two) on the roof.
Regards,
Dirk
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