ᐅ Which lambda value is relevant for insulation?

Hello everyone!

I have been trying to find information about the relevant lambda values for quite some time but haven’t had any luck. I am building my house with aerated concrete, but I am not sure whether I should use the thermal conductivity λ10,dry (W/mK) 0.072 or the design thermal conductivity λ (W/mK) 0.08.

This is important from the perspective of the exterior wall thickness. If I calculate with the dry value, a 30 cm (12 inches) thick wall would be sufficient (U-value = 0.230), but using the design value, it would be (U-value = 0.255).

Thank you very much for your time!

Best regards,
Johann

If I remember correctly, the stone with a lambda value of 0.08 is not available in 30cm (12 inches), but only from 36.5cm (14 inches) upwards.

For the Building Energy Act / KfW / thermal insulation verification / energy performance certificate, ALWAYS use the design value. The nominal value is only an EU requirement and is not considered in German legislation.

xMisterDx schrieb:

If I remember correctly, the block with a lambda value of 0.08 is not available in 30cm (12 inches), only from 36.5cm (14 inches) upwards.

Not with Ytong, but bauroc does offer it. The cost is about five times lower than with Ytong.

dertill schrieb:

For the Building Energy Act / KfW / thermal insulation verification / energy performance certificate, ALWAYS use the design value. The nominal value is just EU paperwork and is not considered in German legislation.

Thank you very much for the clarification. I’m a bit embarrassed, as I’ve been dealing with this topic for over three years but could never find anything about it.