ᐅ Thermal Insulation, Energy Saving Regulations, KFW 70 / 55 / 40 – Your Experiences
Created on: 17 Feb 2015 17:09
H
Häuslebau3r
Hello everyone, as we would say here,
since I have now become quite engaged with this forum and am interested in more and more topics, the question of the right and “best” insulation has come up for me recently (still purely out of interest for now, but surely also practical at some point). I deliberately put the word best in quotation marks because there will always be different preferences and use cases.
I am fully aware that a standard house usually does not require insulation below U=0.14 W/(m²K). Therefore, I tried to look up the following values regarding the energy-saving regulations and the KfW houses 70 / 55 / 40.
I came up with the following values for the thermal transmittance coefficient:
Reference building according to Energy Saving Ordinance 2014
U-value | Roof 0.20 W/(m²K), Windows 1.30 W/(m²K), Exterior wall 0.28 W/(m²K), Basement wall 0.35 W/(m²K), Floor slab 0.35 W/(m²K)
KfW Efficiency House 70
U-value | Roof 0.17 W/(m²K), Windows 0.90 W/(m²K), Exterior wall 0.23 W/(m²K), Basement wall 0.25 W/(m²K), Floor slab 0.25 W/(m²K)
KfW Efficiency House 55
U-value | Roof 0.17 W/(m²K), Windows 0.90 W/(m²K), Exterior wall 0.18 W/(m²K), Basement wall 0.25 W/(m²K), Floor slab 0.25 W/(m²K)
KfW Efficiency House 40
U-value | Roof 0.15 W/(m²K), Windows 0.80 W/(m²K), Exterior wall 0.14 W/(m²K), Basement wall 0.20 W/(m²K), Floor slab 0.20 W/(m²K)
With the above values, it becomes clear what needs to be done regarding home insulation to meet certain standards. As mentioned above, other factors also play a role, such as roof, upper and ground floor windows, possibly the ceiling in the upper floor, exterior wall including roller shutter box, exterior door, exterior wall, and floor slab. But you have to start somewhere.
What I am curious about as a layperson is the comparison between the KfW 70 standard and the KfW 55 regarding the exterior wall. For me, this point represents basically the only difference related to the values mentioned above. Of course, you are also welcome to share your information and experience regarding windows, for example.
To achieve an exterior wall U-value of about 0.18 W/(m²K), there seem to be different options, as I have read in other threads, such as:
For me personally, only the monolithic wall construction is really an option. Of course, you have to consider that you end up with, for example, a 40cm (16 inches) thick wall to achieve certain values. Often, the windows are then described as “loophole-like” because there is so much material around them. How did you decide, or how would you evaluate this from your experience?
What types of blocks or bricks have you had good or bad experiences with? For example,
Now, go ahead and type away!
since I have now become quite engaged with this forum and am interested in more and more topics, the question of the right and “best” insulation has come up for me recently (still purely out of interest for now, but surely also practical at some point). I deliberately put the word best in quotation marks because there will always be different preferences and use cases.
I am fully aware that a standard house usually does not require insulation below U=0.14 W/(m²K). Therefore, I tried to look up the following values regarding the energy-saving regulations and the KfW houses 70 / 55 / 40.
I came up with the following values for the thermal transmittance coefficient:
Reference building according to Energy Saving Ordinance 2014
U-value | Roof 0.20 W/(m²K), Windows 1.30 W/(m²K), Exterior wall 0.28 W/(m²K), Basement wall 0.35 W/(m²K), Floor slab 0.35 W/(m²K)
KfW Efficiency House 70
U-value | Roof 0.17 W/(m²K), Windows 0.90 W/(m²K), Exterior wall 0.23 W/(m²K), Basement wall 0.25 W/(m²K), Floor slab 0.25 W/(m²K)
KfW Efficiency House 55
U-value | Roof 0.17 W/(m²K), Windows 0.90 W/(m²K), Exterior wall 0.18 W/(m²K), Basement wall 0.25 W/(m²K), Floor slab 0.25 W/(m²K)
KfW Efficiency House 40
U-value | Roof 0.15 W/(m²K), Windows 0.80 W/(m²K), Exterior wall 0.14 W/(m²K), Basement wall 0.20 W/(m²K), Floor slab 0.20 W/(m²K)
With the above values, it becomes clear what needs to be done regarding home insulation to meet certain standards. As mentioned above, other factors also play a role, such as roof, upper and ground floor windows, possibly the ceiling in the upper floor, exterior wall including roller shutter box, exterior door, exterior wall, and floor slab. But you have to start somewhere.
What I am curious about as a layperson is the comparison between the KfW 70 standard and the KfW 55 regarding the exterior wall. For me, this point represents basically the only difference related to the values mentioned above. Of course, you are also welcome to share your information and experience regarding windows, for example.
To achieve an exterior wall U-value of about 0.18 W/(m²K), there seem to be different options, as I have read in other threads, such as:
- Monolithic wall construction
- Functional exterior wall
- Double-shell exterior wall
For me personally, only the monolithic wall construction is really an option. Of course, you have to consider that you end up with, for example, a 40cm (16 inches) thick wall to achieve certain values. Often, the windows are then described as “loophole-like” because there is so much material around them. How did you decide, or how would you evaluate this from your experience?
What types of blocks or bricks have you had good or bad experiences with? For example,
- Aerated concrete plan block NeoStone U-value 0.17 W/(m²K)
- Aerated concrete plan block “SK08” U-value up to 0.18 W/(m²K)
- ThermoPlan MZ8 (mineral wool) – 42.5 cm (17 inches) 0.18 W/(m²K)
- Poroton T9 – 36.5 cm (14 inches) 0.23 W/(m²K) – therefore only suitable for KfW 70
- Poroton T8 – 42.5 cm (17 inches) 0.18 W/(m²K)
- Poroton T8 – 49 cm (19 inches) 0.15 W/(m²K)
- Poroton T7 – 42.5 cm (17 inches) 0.15 W/(m²K)
- UNIPOR W09 - Approval Z-17.1.-1042 | 0.20 W/(m²K) – therefore only suitable for KfW 70
- UNIPOR WS07 CORISO | Approval Z-17.1.-1074 0.18 W/(m²K)
- Ytong aerated concrete 0.07 – 36.5 cm (14 inches) 0.18 W/(m²K)
- Ytong aerated concrete 0.08 – 42.5 cm (17 inches) 0.18 W/(m²K)
- Ytong aerated concrete 0.09 – 48 cm (19 inches) 0.18 W/(m²K)
Now, go ahead and type away!
EveundGerd19 Feb 2015 08:53Häuslebau3r schrieb:
May I ask which type of Ytong block you used?
I assume your wall’s U-value is around 0.20 to 0.25, or how thick was your block?
For me, it’s similar—I don’t really want to build with ETICS (external thermal insulation composite system), so the choice of "block" is more important to me than it might be for others.
Did you notice any major differences when looking for a general contractor (GC) based on the type of block? Hello, of course you may ask.
Our block is a 30cm (12 inches) Ytong Thermoblock. According to the manufacturer, the U-value of the block is 0.29 when unplastered.
The next options would have been the 36cm (14 inches) block, followed by the 42.5cm (17 inches) block.
We are not fans of the “airtightness race” and calculated the effort versus benefit for ourselves. That’s why we went with double-glazing. The window had to match the block, and a triple-glazed window would not only have been disproportionately expensive but also did not fit well with the block we chose.
The expert who visited us on Monday said our glazing is excellent, the windows are high-quality products, and that it’s better to invest in good double-glazing than in cheap triple-glazing.
Incidentally, the window manufacturer friend next door agrees with this view as well!
Finding a general contractor experienced in building with Ytong was not that difficult. We are from Koblenz, and the model home center in Mülheim-Kärlich is close by. After two years of planning, gathering information, and having various meetings there, we narrowed our choice down to: Massivhaus Mittelrhein and Town & Country.
Who we are currently building with is mentioned in our build diary, which is posted here.
Häuslebau3r19 Feb 2015 17:13EveundGerd schrieb:
Hello, of course you can ask questions.
Our block is a 30 cm (12 inch) Ytong Thermoblock. According to the manufacturer, the U-value of the block is 0.29 without plaster.
The next best blocks would have been the 36 cm (14 inch) followed by the 42.5 cm (17 inch).
We are not fans of airtightness extremes and have weighed the effort versus benefit for ourselves. That’s also why we chose double glazing. The window needed to match the block, and a triple-glazed unit would not only have been disproportionately expensive, but it also didn’t suit the block we wanted.
The expert who visited us on Monday said our glazing is top quality, the windows are a premium product, and that it’s better to invest in good double glazing than in cheap triple glazing. Our window manufacturer friend next door agrees with that, by the way!
Finding a general contractor who uses Ytong was not so difficult. We live near Koblenz, and the model home center in Mülheim-Kärlich is not far from us. After two years of planning, gathering information, and various discussions there... In the end, our options were: Massivhaus Mittelrhein and Town & Country.
Who we are currently building with is detailed in our build diary, which is posted here.Ah, okay, great THANKS for the information!
Regarding the model home search, we’ve planned to visit a model home park nearby this coming weekend. By coincidence, we found a model home that really comes close to our “dream house” in the prefab home world in Wuppertal. We’ll be visiting relatives in Bad Neuenahr-Ahrweiler during the first week of May—you probably know it—and then we’ll take a day to go there. The next closest model home parks for us would be in Nuremberg and Munich or Ingolstadt. But that particular house is in Wuppertal.
As you said, in the end it will come down to weighing what is economical and what we can afford. Because it doesn’t make sense to take out a loan 50,000 euros more just to build KfW 55 standard and feel proud about having a “green thumb.”
I’ll check out your diary right away.
D
DragonyxXL23 May 2016 11:19@Häuslebau3r :
Have you made any further progress with the wall construction? We are planning a KfW55 bungalow with a ground source heat pump and controlled ventilation with heat recovery. 75% of the window area faces SE/SW, 25% NE/NW. We want a monolithic wall design, but our structural engineer said that KfW55 is not achievable with a 36.5cm (14.4 inches) aerated concrete block. In his calculation, he used an exterior wall made of 24cm (9.4 inches) aerated concrete (0.09 W/mK) plus 12cm (4.7 inches) mineral wool insulation (0.032 W/mK). This results in a U-value (according to ISO 6946) of 0.145 W/m²K.
Calculation results
Qp reference building 94.45 kWh/(m²a)
Qp building 48.38 kWh/(m²a)
Relative to specified Qp reference/target value 51% / 55%
Primary energy demand requirements fulfilled
Ht' reference building 0.336 W/(m²K)
Ht' building 0.234 W/(m²K)
Relative to specified Ht' reference/target value 70% / 70%
Thermal insulation requirements fulfilled
Could the structural engineer be right that it won’t work with a 36.5cm (14.4 inches) aerated concrete block?
Have you made any further progress with the wall construction? We are planning a KfW55 bungalow with a ground source heat pump and controlled ventilation with heat recovery. 75% of the window area faces SE/SW, 25% NE/NW. We want a monolithic wall design, but our structural engineer said that KfW55 is not achievable with a 36.5cm (14.4 inches) aerated concrete block. In his calculation, he used an exterior wall made of 24cm (9.4 inches) aerated concrete (0.09 W/mK) plus 12cm (4.7 inches) mineral wool insulation (0.032 W/mK). This results in a U-value (according to ISO 6946) of 0.145 W/m²K.
Calculation results
Qp reference building 94.45 kWh/(m²a)
Qp building 48.38 kWh/(m²a)
Relative to specified Qp reference/target value 51% / 55%
Primary energy demand requirements fulfilled
Ht' reference building 0.336 W/(m²K)
Ht' building 0.234 W/(m²K)
Relative to specified Ht' reference/target value 70% / 70%
Thermal insulation requirements fulfilled
Could the structural engineer be right that it won’t work with a 36.5cm (14.4 inches) aerated concrete block?
Häuslebau3r7 Jun 2016 12:31Hello @DragonyxXL
I have to admit that I haven’t followed up on this topic recently, as our planning will only start in the winter/spring of next year. Therefore, I can’t provide any additional details about the values of the bricks right now. If you’re unsure, just ask somewhere else as well to get a second opinion. Often, several factors are involved, not just the thickness of the bricks.
I will definitely keep following this topic here as soon as you have more information.
Best regards, Andi
I have to admit that I haven’t followed up on this topic recently, as our planning will only start in the winter/spring of next year. Therefore, I can’t provide any additional details about the values of the bricks right now. If you’re unsure, just ask somewhere else as well to get a second opinion. Often, several factors are involved, not just the thickness of the bricks.
I will definitely keep following this topic here as soon as you have more information.
Best regards, Andi
We are currently building a KFW55 house according to the 2016 Energy Saving Ordinance in Bavaria.
I would not have accepted external insulation and was determined from the start to use solid brick construction.
The brick being used is the Leipfinger Bader Unipor W08 with a thickness of 36.5 cm (14 inches). This brick fully meets the KFW55 requirements for exterior walls. The brick is hollow and therefore not as expensive.
The windows are triple-glazed with a U-value of 0.5 W/m²K, which would have been standard anyway with my builder, even without KFW70/55 standards.
The basement slab and the basement itself are insulated with Styrodur (10 cm (4 inches)), which under the 2014 Energy Saving Ordinance for KFW70 would not have been necessary under the slab. So this added additional costs on top of the brick.
In our region, I usually only see Ytong used in multi-unit residential buildings and always with external insulation. To me, this indicates it is a cheaper construction method compared to using proper bricks. Therefore, it is not an alternative for me.
Overall, upgrading from KFW70 (2014) to KFW55 (2016) was economically reasonable for me, since the additional costs are offset by the lower-interest KFW loan (higher initial investment but paid off faster), and in the long run, I simply have a better building envelope.
I would not have accepted external insulation and was determined from the start to use solid brick construction.
The brick being used is the Leipfinger Bader Unipor W08 with a thickness of 36.5 cm (14 inches). This brick fully meets the KFW55 requirements for exterior walls. The brick is hollow and therefore not as expensive.
The windows are triple-glazed with a U-value of 0.5 W/m²K, which would have been standard anyway with my builder, even without KFW70/55 standards.
The basement slab and the basement itself are insulated with Styrodur (10 cm (4 inches)), which under the 2014 Energy Saving Ordinance for KFW70 would not have been necessary under the slab. So this added additional costs on top of the brick.
In our region, I usually only see Ytong used in multi-unit residential buildings and always with external insulation. To me, this indicates it is a cheaper construction method compared to using proper bricks. Therefore, it is not an alternative for me.
Overall, upgrading from KFW70 (2014) to KFW55 (2016) was economically reasonable for me, since the additional costs are offset by the lower-interest KFW loan (higher initial investment but paid off faster), and in the long run, I simply have a better building envelope.
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