Hello,
I would like to understand the basic construction structure of a KFW 55 house.
I know it needs precise calculations, but I’m interested in the approximate assemblies. All other details will of course be calculated individually. I just want to get an overview of what must be done additionally according to my construction specification, for example, changing from 17.5cm (7 inches) aerated concrete to 24cm (9.5 inches) aerated concrete. I am mainly interested in the key components.
Wall structure?
Insulation in the attic?
Insulation in the roof space?
Construction and insulation of the base slab?
Triple-glazed windows
Heating system (air-source heat pump or gas boiler with solar)?
Ventilation system?
Missing elements?
How did you realize your KFW 55 new build? What are the central components?
Best regards
I would like to understand the basic construction structure of a KFW 55 house.
I know it needs precise calculations, but I’m interested in the approximate assemblies. All other details will of course be calculated individually. I just want to get an overview of what must be done additionally according to my construction specification, for example, changing from 17.5cm (7 inches) aerated concrete to 24cm (9.5 inches) aerated concrete. I am mainly interested in the key components.
Wall structure?
Insulation in the attic?
Insulation in the roof space?
Construction and insulation of the base slab?
Triple-glazed windows
Heating system (air-source heat pump or gas boiler with solar)?
Ventilation system?
Missing elements?
How did you realize your KFW 55 new build? What are the central components?
Best regards
B
Bauexperte8 Mar 2016 16:45Hello,
Looking at KfW 55 only from the perspective of the subsidy of €100,000 per housing unit is also the wrong approach. Compared to the former KfW 70 standard or the current Energy Saving Regulation, and regardless of the house size, you will not save enough on energy costs to make this investment financially worthwhile. Building according to the current Energy Saving Regulation is, by the way, not a bad decision.
There is no single “KfW 55” solution for every house type or provider, so it is not very helpful when users describe their different approaches here; furthermore, each provider uses a different cost calculation. Basically, KfW 55 consists of the building’s structure, insulation, and technical systems. Achieving this standard by using gas heating is not cost-effective compared to other results. So, if your provider relies on that technology, it will be expensive. If your provider already offers an air-to-water heat pump as standard and you are already convinced of installing a controlled ventilation system with heat recovery, the additional costs are manageable.
In short – you lack practical knowledge. Have more consultation meetings, attend trade fairs and/or lectures, so you can become more confident about what you really want to build.
Regards, Bauexperte
nils1985 schrieb:I have been following your questions here for quite some time and am increasingly convinced that you are approaching this the wrong way; aside from the fact that you obviously lack knowledge. The latter is not a problem – you are a prospective homeowner, not a building expert; and understandably uncertain. However, it is not productive for you to raise various questions here and there without a clear direction.
I would like to know the basic construction concept of a KfW 55 house.
Looking at KfW 55 only from the perspective of the subsidy of €100,000 per housing unit is also the wrong approach. Compared to the former KfW 70 standard or the current Energy Saving Regulation, and regardless of the house size, you will not save enough on energy costs to make this investment financially worthwhile. Building according to the current Energy Saving Regulation is, by the way, not a bad decision.
There is no single “KfW 55” solution for every house type or provider, so it is not very helpful when users describe their different approaches here; furthermore, each provider uses a different cost calculation. Basically, KfW 55 consists of the building’s structure, insulation, and technical systems. Achieving this standard by using gas heating is not cost-effective compared to other results. So, if your provider relies on that technology, it will be expensive. If your provider already offers an air-to-water heat pump as standard and you are already convinced of installing a controlled ventilation system with heat recovery, the additional costs are manageable.
In short – you lack practical knowledge. Have more consultation meetings, attend trade fairs and/or lectures, so you can become more confident about what you really want to build.
Regards, Bauexperte
So far, there is a strong opinion here that a KfW55 house with a gas condensing boiler is not possible. However, according to the KfW, this is different if the new building is constructed using the values of the reference house.
Excerpt from KfW:
Alternative proof of a KfW Efficiency House 55 based on reference values The requirements for a KfW Efficiency House 55 are met if the following listed constructional and system technology requirements (reference values) are implemented. In this case, a calculated proof for the KfW Efficiency House 55 is not necessary.
1.) The following requirements for the respective individual components of the thermal building envelope must be observed. The requirements regarding the execution of thermal bridges as well as the airtightness of the building envelope must be met.
• Roof surfaces, top floor ceiling, dormers U ≤ 0.14 W/(m² K)
• Windows and other transparent components Uw ≤ 0.90 W/(m² K)
• Exterior walls, floor slabs below against outdoor air U ≤ 0.20 W/(m² K)
• Other opaque components (basement ceilings, walls and ceilings to unheated rooms, wall and floor surfaces against the ground, etc.) U ≤ 0.25 W/(m² K)
• Doors (basement and exterior doors) UD ≤ 1.2 W/(m² K)
• Avoidance of thermal bridges ΔUWB ≤ 0.035 W/(m² K)
• Airtightness of the building envelope n50 ≤ 1.5 h-1
2.) Regarding the building services, one of the six following system concepts must be implemented. The location of the heat generator or heat transfer station must be within the thermal building envelope, and there must be a central domestic hot water system. A domestic hot water circulation is allowed.
1. Condensing boiler, solar domestic hot water preparation (standard values according to DIN V 4701-10), central ventilation system with heat recovery (heat delivery rate > 80%)
2. District heating with certified primary energy factor fp ≤ 0.7, central ventilation system with heat recovery (heat delivery rate > 80%)
3. Central biomass heating system based on wood pellets, wood chips, or firewood
...
After reading a few building specifications, the wall construction and windows already meet the requirements. For the rest, only additional insulation would be needed. In my opinion, that shouldn’t be very expensive.
What are your thoughts on this?
Excerpt from KfW:
Alternative proof of a KfW Efficiency House 55 based on reference values The requirements for a KfW Efficiency House 55 are met if the following listed constructional and system technology requirements (reference values) are implemented. In this case, a calculated proof for the KfW Efficiency House 55 is not necessary.
1.) The following requirements for the respective individual components of the thermal building envelope must be observed. The requirements regarding the execution of thermal bridges as well as the airtightness of the building envelope must be met.
• Roof surfaces, top floor ceiling, dormers U ≤ 0.14 W/(m² K)
• Windows and other transparent components Uw ≤ 0.90 W/(m² K)
• Exterior walls, floor slabs below against outdoor air U ≤ 0.20 W/(m² K)
• Other opaque components (basement ceilings, walls and ceilings to unheated rooms, wall and floor surfaces against the ground, etc.) U ≤ 0.25 W/(m² K)
• Doors (basement and exterior doors) UD ≤ 1.2 W/(m² K)
• Avoidance of thermal bridges ΔUWB ≤ 0.035 W/(m² K)
• Airtightness of the building envelope n50 ≤ 1.5 h-1
2.) Regarding the building services, one of the six following system concepts must be implemented. The location of the heat generator or heat transfer station must be within the thermal building envelope, and there must be a central domestic hot water system. A domestic hot water circulation is allowed.
1. Condensing boiler, solar domestic hot water preparation (standard values according to DIN V 4701-10), central ventilation system with heat recovery (heat delivery rate > 80%)
2. District heating with certified primary energy factor fp ≤ 0.7, central ventilation system with heat recovery (heat delivery rate > 80%)
3. Central biomass heating system based on wood pellets, wood chips, or firewood
...
After reading a few building specifications, the wall construction and windows already meet the requirements. For the rest, only additional insulation would be needed. In my opinion, that shouldn’t be very expensive.
What are your thoughts on this?
For the thermal bridge verification, either an exact calculation must be done, or every detail must strictly follow the KFW thermal bridge catalog. To my knowledge, for example, only one roof window per roof side is allowed.
KFW55 standard with gas and solar according to reference values is easily achievable. However, note that solar water heating according to DIN V 4701-10 often requires more than the usual two solar collectors depending on the house size. I believe I once calculated it for our planned house, and if I remember correctly, it came to four solar collectors. This leads to the usual stagnation issue, although the manufacturer from Allendorf claims to have solutions for this.
For windows, the U-value of the entire window applies, not the often quoted U-value of the glass alone. Achieving 0.14 (2.5 BTU/(h·ft²·°F)) for the top floor ceiling certainly isn't very expensive. If it concerns pitched roofs, additional insulation below the rafters may need to be considered, but even that should not be too costly (relatively speaking, compared to house + land + ancillary building costs).
KFW55 standard with gas and solar according to reference values is easily achievable. However, note that solar water heating according to DIN V 4701-10 often requires more than the usual two solar collectors depending on the house size. I believe I once calculated it for our planned house, and if I remember correctly, it came to four solar collectors. This leads to the usual stagnation issue, although the manufacturer from Allendorf claims to have solutions for this.
For windows, the U-value of the entire window applies, not the often quoted U-value of the glass alone. Achieving 0.14 (2.5 BTU/(h·ft²·°F)) for the top floor ceiling certainly isn't very expensive. If it concerns pitched roofs, additional insulation below the rafters may need to be considered, but even that should not be too costly (relatively speaking, compared to house + land + ancillary building costs).
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