vapor resistance factor_air layer

[nahamieh]

Dear Wufi Forum team,
I am writing to request clarification regarding the vapor resistance factor of 0.23 for a 70 mm air layer between two non-metallic materials, as mentioned in your documentation. Typically, the vapor resistance factor (μ) is defined as the permeability of a material to water vapor over that of the air. And here since we are talking about air, the vapor resistance factor should be equal to 1. Could you please explain why it is listed as 0.23? Am I missing any specific considerations in this context?
In fact, I am modelling hollow concrete blocks with two ranges of air cavities (each of 74 mm) and I intend to represent these cavities as air layers. Could you provide guidance on accurately determining the vapor resistance factor for this application?
Thank you for your assistance. I look forward to your response.
Best regards,
Nancy Hamieh

[Christian Bludau]

Dear Nancy
the air layers contain effective values for convection and radiation. You can find a description on how they are determined in the WUFI Program help. Press the F1-key somewhere in the software and search the index for air layers. Please also see the material information in the material itself.
Christian