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?
S
Sebastian7918 Apr 2015 11:08Yes? Of course, you have a difference, and I certainly don’t want to claim our 14 cm (5.5 inches) insulation as the optimal standard – but calculate this: you get a difference of 0.044 W/m²K. Now convert that into annual savings and then compare it to the additional costs (not just for the insulation material).
There is a lot of misleading information in this… unfortunately.
There is a lot of misleading information in this… unfortunately.
L
LittleWulf18 Apr 2015 11:37A question came to my mind yesterday: Is it possible to achieve the KfW 70 standard without solar thermal systems by using controlled ventilation with heat recovery along with the gas heating? Because the solar thermal system was also described to us as not really useful or necessary.
Yes... Use the search function or Wikipedia. Solar thermal systems are not required to achieve KFW70.
According to information found online, at a 60% coverage rate (60% of the energy for domestic hot water comes from solar), you save about €140 per year (see Thorben Frahm). The cost for 5 m² (about 54 ft²) is €3,760 according to the same website (assumption: 160 liters (42 gallons) per day, 60% coverage). Without subsidies, the system would need to be on the roof for 31 years (with €20 per year maintenance costs, excluding interest)... so purely financially, it’s rather not very cost-effective for new builds.
In our village, for example, such systems are still subsidized at €40 per m² (about $40 per 10.8 ft²)! Still, it doesn’t seem very practical.
According to information found online, at a 60% coverage rate (60% of the energy for domestic hot water comes from solar), you save about €140 per year (see Thorben Frahm). The cost for 5 m² (about 54 ft²) is €3,760 according to the same website (assumption: 160 liters (42 gallons) per day, 60% coverage). Without subsidies, the system would need to be on the roof for 31 years (with €20 per year maintenance costs, excluding interest)... so purely financially, it’s rather not very cost-effective for new builds.
In our village, for example, such systems are still subsidized at €40 per m² (about $40 per 10.8 ft²)! Still, it doesn’t seem very practical.
Achieving KfW 70 with a gas heating system without solar thermal energy is very difficult (or perhaps not practical). A typical prefab house builder will probably not manage this and, more importantly, may not be very motivated to do so. The building must be very well insulated and meet the standards of a good passive house in other respects as well (orientation, planning, etc.).
Our house will significantly exceed the insulation values of a KfW 55 house. However, due to the gas heating, KfW 70 is still not achievable without solar thermal energy. Although we do not have controlled mechanical ventilation, according to our energy consultant, this alone would not have been sufficient to replace the solar system. The solar system is now included mainly for environmental protection. It is certainly not economical (and neither is the controlled mechanical ventilation, by the way).
I also find Lexmaul’s point interesting. Building insulation will eventually reach a peak. But considering that over 50% of all waste production in Germany comes from the construction sector, I believe people should carefully consider the materials they use in their homes. The energy consumption of the construction industry is also enormous, and there is great potential for saving energy there. I’m not sure if it’s the right approach to insulate buildings heavily using resource-intensive and waste-heavy building materials, only to face the problem in a few decades of dealing with all that hazardous waste.
Therefore, I advocate that discussions about KfW should not only focus on financial aspects but also consider the environment: after all, that should be the real purpose of this support, right?!
Our house will significantly exceed the insulation values of a KfW 55 house. However, due to the gas heating, KfW 70 is still not achievable without solar thermal energy. Although we do not have controlled mechanical ventilation, according to our energy consultant, this alone would not have been sufficient to replace the solar system. The solar system is now included mainly for environmental protection. It is certainly not economical (and neither is the controlled mechanical ventilation, by the way).
I also find Lexmaul’s point interesting. Building insulation will eventually reach a peak. But considering that over 50% of all waste production in Germany comes from the construction sector, I believe people should carefully consider the materials they use in their homes. The energy consumption of the construction industry is also enormous, and there is great potential for saving energy there. I’m not sure if it’s the right approach to insulate buildings heavily using resource-intensive and waste-heavy building materials, only to face the problem in a few decades of dealing with all that hazardous waste.
Therefore, I advocate that discussions about KfW should not only focus on financial aspects but also consider the environment: after all, that should be the real purpose of this support, right?!
Honestly... what exactly should politicians do to reduce energy consumption? It basically comes down to insulation or promoting environmentally friendly energy production... especially since the latter also aims to make the country more independent (more of a political-strategic consideration).
This is working well... houses now have an actual heating load of 6 kW instead of 30 kW as before! You really have to let that sink in.
This is working well... houses now have an actual heating load of 6 kW instead of 30 kW as before! You really have to let that sink in.
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