ᐅ How much real savings can be achieved through better wall insulation?
Created on: 9 Dec 2016 10:46
J
Judyyy
Hello everyone,
As some of you already know, I am planning a new build to KfW 55 standards, which I consider a minimum requirement and would ideally like to achieve even better.
We want to build monolithically with Ytong. We also want to have the best possible windows. Regarding floor and roof insulation, I believe that the improvement from KfW 55 to 40 won’t save you much energy. I saw a construction diary online where the builder paid roughly €2,500 (~ $2,700) extra (+ €5,000 (~ $5,400) repayment subsidy) for improved roof and floor insulation but had an already very good timber frame wall. However, prices for Ytong vary quite a lot, so my question is which type of block makes financial sense.
For example, for my house, the costs are approximately:
- 36.5cm (14.4 inches), lambda 0.09, U-value 0.23, about €19,500 (~ $21,000)
- 42.5cm (16.7 inches), lambda 0.09, U-value 0.20, about €22,700 (~ $24,500)
- 42.5cm (16.7 inches), lambda 0.08, U-value 0.18, about €26,800 (~ $28,900)
- 48.0cm (18.9 inches), lambda 0.08, U-value 0.16, about €30,300 (~ $32,700)
- 48.0cm (18.9 inches), lambda 0.07, U-value 0.14, about €42,400 (~ $45,700)
These prices are from price lists found online.
I think the last block with a U-value of 0.14 and an extra cost of roughly €12,000 (~ $13,000) can be ruled out immediately.
I have two questions:
1. If we stick to KfW 55, up to which block thickness or quality does the extra cost make financial sense?
I’m generously assuming a timeframe of 30 years, which should be the period to pay off the house. The goal is to finish within 25 years.
2. Is it possible to reach KfW 40 standards with the block that has a U-value of 0.16?
A brief overview of the house:
- 180 m² (1,938 sq ft) living and usable space
- Probably a ground source heat pump with trench collectors
- Probably photovoltaics
- Probably controlled mechanical ventilation with heat recovery
- At least KfW 55 standard
I hope you can help me with this.
Best regards,
Judyyy
As some of you already know, I am planning a new build to KfW 55 standards, which I consider a minimum requirement and would ideally like to achieve even better.
We want to build monolithically with Ytong. We also want to have the best possible windows. Regarding floor and roof insulation, I believe that the improvement from KfW 55 to 40 won’t save you much energy. I saw a construction diary online where the builder paid roughly €2,500 (~ $2,700) extra (+ €5,000 (~ $5,400) repayment subsidy) for improved roof and floor insulation but had an already very good timber frame wall. However, prices for Ytong vary quite a lot, so my question is which type of block makes financial sense.
For example, for my house, the costs are approximately:
- 36.5cm (14.4 inches), lambda 0.09, U-value 0.23, about €19,500 (~ $21,000)
- 42.5cm (16.7 inches), lambda 0.09, U-value 0.20, about €22,700 (~ $24,500)
- 42.5cm (16.7 inches), lambda 0.08, U-value 0.18, about €26,800 (~ $28,900)
- 48.0cm (18.9 inches), lambda 0.08, U-value 0.16, about €30,300 (~ $32,700)
- 48.0cm (18.9 inches), lambda 0.07, U-value 0.14, about €42,400 (~ $45,700)
These prices are from price lists found online.
I think the last block with a U-value of 0.14 and an extra cost of roughly €12,000 (~ $13,000) can be ruled out immediately.
I have two questions:
1. If we stick to KfW 55, up to which block thickness or quality does the extra cost make financial sense?
I’m generously assuming a timeframe of 30 years, which should be the period to pay off the house. The goal is to finish within 25 years.
2. Is it possible to reach KfW 40 standards with the block that has a U-value of 0.16?
A brief overview of the house:
- 180 m² (1,938 sq ft) living and usable space
- Probably a ground source heat pump with trench collectors
- Probably photovoltaics
- Probably controlled mechanical ventilation with heat recovery
- At least KfW 55 standard
I hope you can help me with this.
Best regards,
Judyyy
Search for "kfw 40 ytong." You will find a PDF from YTONG where the company addresses the 2014 Energy Saving Ordinance. It includes configuration examples showing how the relevant KfW standards can be achieved using their materials. According to this, for KfW 40, the 48cm (19 inches) block with a U-value of 0.14 is required if you want to stick with a monolithic construction.
Whether the additional cost is as significant as you described can only be confirmed by your potential building partner. We are planning for KfW 55 and will certainly evaluate the extra cost compared to KfW 40 as well, especially since our planning includes a ground-source heat pump, controlled ventilation with heat recovery, and photovoltaics, so our Qp value already comes close to passive house standards.
However, I do not expect it to be economically viable. If you want KfW 40, in my opinion, monolithic construction represents the upper limit. Simply adding thicker expanded polystyrene insulation is much easier after all.
Whether the additional cost is as significant as you described can only be confirmed by your potential building partner. We are planning for KfW 55 and will certainly evaluate the extra cost compared to KfW 40 as well, especially since our planning includes a ground-source heat pump, controlled ventilation with heat recovery, and photovoltaics, so our Qp value already comes close to passive house standards.
However, I do not expect it to be economically viable. If you want KfW 40, in my opinion, monolithic construction represents the upper limit. Simply adding thicker expanded polystyrene insulation is much easier after all.
These are just examples. The actual calculation depends on the building, its shape, orientation, etc., and is carried out by the energy consultant. For guidance, you can refer to the reference value calculation for KfW 55, which ultimately represents a simplified procedure.
The primary energy demand, mainly influenced by building services systems, as well as the heat loss through the building envelope, affected by the selected construction materials, must meet the required standards.
The primary energy demand, mainly influenced by building services systems, as well as the heat loss through the building envelope, affected by the selected construction materials, must meet the required standards.
That’s why we actually brought an architect on board who is also an energy consultant.
But he seems to be overwhelmed by the question of the cost difference between KfW 55 and 40. 🙄
He says he’ll do it the way I want. 🤨
Architects always seem to be quick to settle for that explanation,...
KfW 40 is not cost-effective. 🙄
But he seems to be overwhelmed by the question of the cost difference between KfW 55 and 40. 🙄
He says he’ll do it the way I want. 🤨
Architects always seem to be quick to settle for that explanation,...
KfW 40 is not cost-effective. 🙄
Is it possible to calculate it like this?
If heating costs are currently 800 € for a KfW 55 building, with heat loss through the exterior walls accounting for 30%, which is 240 €.
If the wall insulation is improved from 0.23 to 0.16 (W/m²K), that’s an improvement of about 30%.
If I reduce the 240 € by 30%, that’s only 72 € saved annually.
Over 50 years, that would be a total saving of just 3,600 €, compared to an additional cost of 10,000 €.
Can the calculation be done like this, or is this completely wrong?
Regards,
Judyyy
If heating costs are currently 800 € for a KfW 55 building, with heat loss through the exterior walls accounting for 30%, which is 240 €.
If the wall insulation is improved from 0.23 to 0.16 (W/m²K), that’s an improvement of about 30%.
If I reduce the 240 € by 30%, that’s only 72 € saved annually.
Over 50 years, that would be a total saving of just 3,600 €, compared to an additional cost of 10,000 €.
Can the calculation be done like this, or is this completely wrong?
Regards,
Judyyy
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