problem in decreasing initial water content

[Pegahbe]

Hello,
I am using WUFI 2D to model a pitched roof which contains cellulose insulation.
The Initial water content of all the layers in the roof is considered to an amount which is equivalent to 80% RH. By the end of model run, the total water content of roof decreases over the years, but I see high water content in the outer side of insulation and the wooden board next to it (more than 20% moisture content).
For the sake of comparison, I decided to reduce initial water content of cellulose (as it is suggested by the supplier), but I can see by the end of run, the total water content of roof increases over the years, and I can not be sure if the results for final water content of insulation and other layers can be reliable in this case.
Can any one help me how can I reduce the initial water content of cellulose without facing such problem?
Thanks,
Pegah.

[Christian Bludau]

Dear Pegah,

every construction, which does not accumulate water reaches steady state conditions after some time. This condition is independent from the initial moisture. If you start with a initial moisture below that steady state the moisture has to increase to reach the steady state, if you start with higher values, it will try out. If you have materials with have a high moisture storage capability the initial moisture may have to redistribute first.

So starting at a lower initial moisture for the cellulose fiber may only have a short time effect on your outer layers.

The behavior of your construction will usual win if you use a adequate vapor control layer (VCL) at the inside. Did you include a VCL in your construction?

Christian