ᐅ Aerated concrete 42.5, thermal conductivity (lambda) 0.08 or 0.09 W/m·K

Hello everyone,

I hope you can help me. I am trying to decide whether to build my exterior walls with 42.5cm (17 inches) aerated concrete blocks with a lambda value of 0.08 or 0.09.
I am not building to KfW standards, and the heating system is gas combined with solar. Is there a significant difference between the two?

Thanks in advance.

Approximately 20-30€ difference in heating costs per year

If you’re not building according to KfW standards, then using a 42cm (16.5 inches) brick doesn’t make any sense at all. But everyone can decide for themselves. I can easily achieve a lambda value of 0.09 or 0.08 with a 36cm (14 inches) brick as well, and that one is also unfilled.

Aerated concrete 425mm (17 inches) Lambda 0.09 = U-value 0.204
Aerated concrete 425mm (17 inches) Lambda 0.08 = U-value 0.182

Aerated concrete 365mm (14 inches) Lambda 0.09 = U-value 0.237
Aerated concrete 365mm (14 inches) Lambda 0.08 = U-value 0.211

If there is no energy standard requirement to meet, I would skip the upgrade. The additional cost is probably in the four-figure range and not worth it.

However, I would consider going with 365mm (14 inches) masonry. That should be sufficient, especially with Lambda 0.08.
The extra cost for the better block should be offset by the reduced thickness, resulting in thinner walls and therefore more living space.

Zaba12 schrieb:

If you’re not building according to KfW standards, then the 42 cm (16.5 inches) brick really doesn’t make much sense. But everyone to their own. Because I can easily achieve a lambda value of 0.09 or 0.08 with a 36 cm (14 inches) brick as well, and that one is also unfilled.

Basically, yes, a 42 cm (16.5 inches) brick is not very economical. But lambda is only the thermal conductivity; of course, a 42 cm (16.5 inches) wall with 0.08 W/(m·K) insulates better than a 36 cm (14 inches) wall with 0.08 W/(m·K).

guckuck2 schrieb:

Aerated concrete 425mm (17 inches) Lambda 0.09 = U-value 0.204
Aerated concrete 425mm (17 inches) Lambda 0.08 = U-value 0.182

Aerated concrete 365mm (14 inches) Lambda 0.09 = U-value 0.237
Aerated concrete 365mm (14 inches) Lambda 0.08 = U-value 0.211

If there is no energy standard to meet, I would skip the upgrade. The additional costs are probably in the four-digit range. Not worth it.

I would consider going with 365mm (14 inches) masonry. That should be sufficient, especially with Lambda 0.08.
The extra cost for the better block should be offset by the reduced thickness, resulting in thinner walls and thus more living space.

The additional costs are about 2000€ for our project. Good point. Thanks!