ᐅ Energy Efficiency Certificate KfW55 – Target KfW40 – Question: Steps & Costs
Created on: 19 Apr 2016 13:26
W
world-e
Hello everyone,
I have a question regarding structural engineering and energy efficiency:
We are currently planning a timber frame house with a basement. A ventilation system is also planned but has not been included in this energy performance calculation. According to the energy certificate, it is currently a KfW55 house. Please see the attached excerpts in the PDF. If more information is needed, please ask.
When I asked the energy consultant what would be necessary to achieve KfW40, he said the basement insulation would need to be 16cm instead of 12cm thick. This would result in the timber frame wall needing to be thicker as well (also for structural reasons). When I asked if the wood fiber insulation on the exterior wall could simply be made thicker (120mm instead of 60mm) to reach a U-value close to 0.11, he replied that this is not possible because the timber studs must rest about two-thirds on the foundation slab or basement ceiling. This would again require a thicker stud. Overall, the additional costs would be around €30,000–40,000, which would never pay off. I was not given any further explanation as to why the costs are this high.
My questions are:
1.) What do you think about these additional costs — can they be realistic?
2.) The wood fiber insulation boards don’t necessarily have to end flush with the outer edge of the concrete, right? They can protrude, correct? If the wood fiber board is thicker, it would just stick out a bit (6cm) without requiring any changes to the timber framing. And if the wood fiber insulation extends outward, wouldn’t the basement insulation be able to be thicker as well?
3.) What other options might I have to achieve KfW40 in a cost-effective way?
I hope you can help me understand this better. Many thanks.
I have a question regarding structural engineering and energy efficiency:
We are currently planning a timber frame house with a basement. A ventilation system is also planned but has not been included in this energy performance calculation. According to the energy certificate, it is currently a KfW55 house. Please see the attached excerpts in the PDF. If more information is needed, please ask.
When I asked the energy consultant what would be necessary to achieve KfW40, he said the basement insulation would need to be 16cm instead of 12cm thick. This would result in the timber frame wall needing to be thicker as well (also for structural reasons). When I asked if the wood fiber insulation on the exterior wall could simply be made thicker (120mm instead of 60mm) to reach a U-value close to 0.11, he replied that this is not possible because the timber studs must rest about two-thirds on the foundation slab or basement ceiling. This would again require a thicker stud. Overall, the additional costs would be around €30,000–40,000, which would never pay off. I was not given any further explanation as to why the costs are this high.
My questions are:
1.) What do you think about these additional costs — can they be realistic?
2.) The wood fiber insulation boards don’t necessarily have to end flush with the outer edge of the concrete, right? They can protrude, correct? If the wood fiber board is thicker, it would just stick out a bit (6cm) without requiring any changes to the timber framing. And if the wood fiber insulation extends outward, wouldn’t the basement insulation be able to be thicker as well?
3.) What other options might I have to achieve KfW40 in a cost-effective way?
I hope you can help me understand this better. Many thanks.
Another question regarding the energy performance certificate:
The 12cm (5 inches) insulation under the slab is not included in the layer assembly and U-values of the used components (p. 40), but it appears in the thermal bridge calculation (p. 11). How is the U-value of 0.164 for the ground slab (p. 2) determined? Is it based on the U-value from the basement floor thermal bridge calculation (p. 11) of 0.183, or on the U-value of 0.365 multiplied by a factor of 0.4–0.5? What is the usual practice? The U-value from the layer assembly and the U-value from the thermal bridge calculation should be identical.
See Keller.pdf or the complete energy performance certificate.
The 12cm (5 inches) insulation under the slab is not included in the layer assembly and U-values of the used components (p. 40), but it appears in the thermal bridge calculation (p. 11). How is the U-value of 0.164 for the ground slab (p. 2) determined? Is it based on the U-value from the basement floor thermal bridge calculation (p. 11) of 0.183, or on the U-value of 0.365 multiplied by a factor of 0.4–0.5? What is the usual practice? The U-value from the layer assembly and the U-value from the thermal bridge calculation should be identical.
See Keller.pdf or the complete energy performance certificate.
Rübe1 schrieb:
The wall construction lacks a clear conceptCould you please explain that in more detail?I downloaded the trial version of the Rowa software.
The 0.164 (floor area, page 2) is the U-value 0.365 of the basement floor (page 40) multiplied by the factor 0.45. So, this calculation does not include perimeter insulation under the slab, whereas the thermal bridge calculation (page 11) does.
What also seems strange to me is the perimeter of 85.0m (page 8). The perimeter should only be 38.5m (for 10.5 x 8.75m). Or is it calculated differently? Maybe someone can briefly explain this to me. Thanks.
The 0.164 (floor area, page 2) is the U-value 0.365 of the basement floor (page 40) multiplied by the factor 0.45. So, this calculation does not include perimeter insulation under the slab, whereas the thermal bridge calculation (page 11) does.
What also seems strange to me is the perimeter of 85.0m (page 8). The perimeter should only be 38.5m (for 10.5 x 8.75m). Or is it calculated differently? Maybe someone can briefly explain this to me. Thanks.
There are updates now, and the required U-values to achieve KfW40 have been calculated. The U-value for the exterior wall should now be 0.11 W/m²K. However, in the calculation, the framing was enlarged and filled with Thermofibre ("Wand_Thermofibre.pdf"). The other idea is to double the thickness of the exterior wood fiber insulation boards to 120mm (5 inches).
Which wall construction is better, or what are the advantages and disadvantages of each? The original wall construction plus 120mm (5 inches) wood fiber insulation boards seems to be the easiest to implement and therefore more cost-effective. Or is there any reason against the option shown in "Wand_120.pdf"?
Thank you.
Which wall construction is better, or what are the advantages and disadvantages of each? The original wall construction plus 120mm (5 inches) wood fiber insulation boards seems to be the easiest to implement and therefore more cost-effective. Or is there any reason against the option shown in "Wand_120.pdf"?
Thank you.
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