Glaser condensation diagram layers compressed together
Posted by Andy Tindale on 29-Mar-22 06:07 PM
Glaser diagrams use the concept of "equivalent thickness of air" on the X-axis which defines the amount of resistance to moisture diffusion relative to the equivalent thickness of air. When layers are compressed together this means that they offer little resistance to moisture diffusion. You should check that the correct moisture diffusion data has been entered on the Materials dialog. For example if a layer has an equivalent thickness of 5m that means that it offers the same diffusion resistance as 5m of air. 

It is usual for materials with high diffusion resistance to be used on the warm side and with lower diffusion resistance on the cold side to minimise the risk of interstitial condensation occurring.

For exampe in the Glaser diagram below the X-axis (Cumulative Equivalent Air Thickness) is dominated by the vapour barrier (yellow layer), while the 2 layers to the right (inside of the wall), which offer little resistance to moisture transfer, are compressed together.