ᐅ Floor Construction for a New Single-Family House KfW55 Standard
Created on: 7 Apr 2016 08:17
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ElBoCaDiLlO
Hello everyone,
this is my first post in the forum. I hope you can help me a bit.
I have planned a prefabricated house, and with the recent changes in the energy saving regulations and since I will be installing an exhaust air heat pump, my insulation requirements have decreased.
To save some money, I wanted to skip the 16cm (6 inches) perimeter insulation under the concrete foundation.
Now, a new energy saving regulation calculation was done. The floor insulation consists of 20cm (8 inches) C20/25 concrete and 8.5cm (3.3 inches) WLG025 insulation under the screed. This results in a U-value of 0.27 W/m²K, which seems quite high for a KfW55 house, doesn’t it?
I’m not very familiar with this, which is also why I handed everything over, but all other values (roof, exterior walls) are around 0.14 W/m²K.
Do you see a simple way to improve the floor insulation, and above all, does it even make sense, or is this value sufficient?
The floors on both ground and upper levels will be fully equipped with underfloor heating.
I don’t have the exact floor structure on hand right now, but I can provide it if needed.
Many thanks and best regards from the sandwich.
this is my first post in the forum. I hope you can help me a bit.
I have planned a prefabricated house, and with the recent changes in the energy saving regulations and since I will be installing an exhaust air heat pump, my insulation requirements have decreased.
To save some money, I wanted to skip the 16cm (6 inches) perimeter insulation under the concrete foundation.
Now, a new energy saving regulation calculation was done. The floor insulation consists of 20cm (8 inches) C20/25 concrete and 8.5cm (3.3 inches) WLG025 insulation under the screed. This results in a U-value of 0.27 W/m²K, which seems quite high for a KfW55 house, doesn’t it?
I’m not very familiar with this, which is also why I handed everything over, but all other values (roof, exterior walls) are around 0.14 W/m²K.
Do you see a simple way to improve the floor insulation, and above all, does it even make sense, or is this value sufficient?
The floors on both ground and upper levels will be fully equipped with underfloor heating.
I don’t have the exact floor structure on hand right now, but I can provide it if needed.
Many thanks and best regards from the sandwich.
S
Sebastian797 Apr 2016 15:07If you are building a KFW55 house, you need a professional consultant – you cannot do the calculations yourself.
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ElBoCaDiLlO7 Apr 2016 15:29That is clear to me. I am just doing some rough calculations here to understand it a bit better.
I am building a prefab house, and they handle all the calculations for the KfW program and so on.
Since the change on April 1st, I was told that perimeter insulation is no longer mandatory to meet the KfW 55 standard. Instead, the 0.025 insulation under the screed is used as compensation.
This was implemented, and a new energy-saving regulation calculation was done, showing 0.268 W/m²K for the floor. I don’t know what the value was before with the 160mm (6.3 inches) perimeter insulation.
The question is "only": Is a U-value of 0.268 W/m²K for a slab-on-ground floor acceptable for a house that will be heated with an exhaust air heat pump?
If that is too high, I would have to try to increase the insulation. According to the manufacturer, increasing the 0.025 insulation thickness is not possible due to the anchoring of wall elements and similar constraints.
Thanks for the help.
I am building a prefab house, and they handle all the calculations for the KfW program and so on.
Since the change on April 1st, I was told that perimeter insulation is no longer mandatory to meet the KfW 55 standard. Instead, the 0.025 insulation under the screed is used as compensation.
This was implemented, and a new energy-saving regulation calculation was done, showing 0.268 W/m²K for the floor. I don’t know what the value was before with the 160mm (6.3 inches) perimeter insulation.
The question is "only": Is a U-value of 0.268 W/m²K for a slab-on-ground floor acceptable for a house that will be heated with an exhaust air heat pump?
If that is too high, I would have to try to increase the insulation. According to the manufacturer, increasing the 0.025 insulation thickness is not possible due to the anchoring of wall elements and similar constraints.
Thanks for the help.
N
nordanney7 Apr 2016 16:26You understand that this change means a TIGHTENING of the requirements. It does not mean you need less insulation!
I would NOT heat a KfW 55 house, where you are also cutting back on insulation, with an exhaust air heat pump. The risk of having to rely on expensive electric heating in winter would be too high for me...
P.S. You’re buying a KfW 55 house. Why are you trying so hard to tell the professionals how to meet the KfW 55 standard? There are many ways to achieve it.
I would NOT heat a KfW 55 house, where you are also cutting back on insulation, with an exhaust air heat pump. The risk of having to rely on expensive electric heating in winter would be too high for me...
P.S. You’re buying a KfW 55 house. Why are you trying so hard to tell the professionals how to meet the KfW 55 standard? There are many ways to achieve it.
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ElBoCaDiLlO7 Apr 2016 17:03nordanney, currently the stricter regulation means that an electric heating system has a greater positive impact on the energy calculation than before, making it easier to meet the kfW requirements when using electric heating.
I am not trying anything here. I was surprised that after the change—which did NOT come from me but from them—the U-value of the floor is so high compared to all others. As I wrote in the first post, my question is whether this value is too high for the exhaust air heat pump.
The suggestion to omit insulation came from the home seller, who claimed that 8cm (3 inches) of the 16cm (6 inches) perimeter insulation no longer makes a difference. Why shouldn’t I agree if it also becomes cheaper for me? Still, I am allowed to wonder why the value suddenly went up and whether I should have stayed with the previous one.
The question remains how significant the difference between 0.268 and 0.204 really is. It’s not only a matter of cost but also energy loss. That equals 0.64 W/m²K over 100m² (1,076 sq ft) at a 20°C (36°F) temperature difference, so 1,280 watts. At 20 cents per kWh, that’s a €2,242 difference per year. Can that really be correct? If I am calculating correctly, why am I being advised to accept something that pays off within a year?
What would be a good U-value for a concrete slab?
I assume that they know what they are doing; I was just surprised and naturally wanted to inform myself. So far, however, I have not received a useful answer, only posts saying I should insulate less, even though this was according to the expert advisor’s suggestion. Something doesn’t seem right here.
In short: Is a U-value of 0.268 W/m²K too high?
I am not trying anything here. I was surprised that after the change—which did NOT come from me but from them—the U-value of the floor is so high compared to all others. As I wrote in the first post, my question is whether this value is too high for the exhaust air heat pump.
The suggestion to omit insulation came from the home seller, who claimed that 8cm (3 inches) of the 16cm (6 inches) perimeter insulation no longer makes a difference. Why shouldn’t I agree if it also becomes cheaper for me? Still, I am allowed to wonder why the value suddenly went up and whether I should have stayed with the previous one.
The question remains how significant the difference between 0.268 and 0.204 really is. It’s not only a matter of cost but also energy loss. That equals 0.64 W/m²K over 100m² (1,076 sq ft) at a 20°C (36°F) temperature difference, so 1,280 watts. At 20 cents per kWh, that’s a €2,242 difference per year. Can that really be correct? If I am calculating correctly, why am I being advised to accept something that pays off within a year?
What would be a good U-value for a concrete slab?
I assume that they know what they are doing; I was just surprised and naturally wanted to inform myself. So far, however, I have not received a useful answer, only posts saying I should insulate less, even though this was according to the expert advisor’s suggestion. Something doesn’t seem right here.
In short: Is a U-value of 0.268 W/m²K too high?
S
Sebastian797 Apr 2016 17:050.06 more – You made a slight calculation error. This also applies to the costs.
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ElBoCaDiLlO7 Apr 2016 18:05oh You’re right BUT ^^ 0.064 W/m²K * 0.2€ * 24h * 365d * 0.001 * 20K * 100 m² (1,076 sq ft) = 224.56€, so the decimal point just shifted Then it looks different again, but there is still no information on whether it actually turns out that way.
Sebastian, what U-value do you have for the floor, for example?
Sebastian, what U-value do you have for the floor, for example?
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