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.
Alex85 schrieb:
You already mentioned the type of blocks you’re building with in another thread (I hope I’m not confusing you now). The blocks mentioned there have a U-value of 0.21 W/(m²·K), which would not meet the requirements for KfW 55 based on the reference value method. Here, you’re writing about the U-value of your floor slab, which perfectly meets the target according to the mentioned method. And, as you say, it’s even a bit better than required.
I’m wondering which building components in your house have U-values that shift the balance in the opposite direction. That really only leaves the roof and windows, with the latter being a tricky and expensive issue if overdone. I’m leaving the front door out of consideration.
I’m genuinely interested since we are currently focusing more on this topic ourselves. It would be great if you could briefly list your values.You’re not confusing me, I’m the one with the 0.08 blocks.
As we know, meeting the KfW 55 standard is a mixed calculation of primary energy demand, energy efficiency, and building materials. Without mechanical ventilation with heat recovery, we probably would have needed extra measures regarding the materials. Thanks to the mechanical ventilation system, we easily meet the minimum requirements in my opinion, and that was the reason we aimed for KfW 55.
Since the energy calculation is quite complex, I hope I’m quoting the correct values. Here are what I consider the most important U-values:
Windows: Ug 0.5, Uw 0.8
Roof: 0.17
Exterior walls: 0.21
Basement walls (plinth): 0.26
Basement walls (below ground): 0.29
Floor slab/basement floor: 0.25
Air/water heat pump (COP 3.7) covers 95% of heating, plus 5% electric auxiliary heating, as well as a mechanical ventilation system with 90% heat recovery.
Calculated annual heating demand is 3,582 kWh.
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