Moisture Storage Function and WVDRF Interpolation

[Mark Jimmy]

Hello,

I was wondering if someone may be able to further explain one phenomenon I am experiencing in WUFI Pro.
This has to do with the moisture storage function (MSF).

I am looking at the moisture content of wooden cladding which is directly fixed to the structure. I seam to have an issue with experience extreme and unrealistic moisture contents during several scenarios.

For reference, I have broken the cladding into three layers; 1) Exterior Paint Layer (1mm), 2) Middle Layer (6mm and Observation layer) 3) Interior Layer (6mm). The wall assembly consists of exterior cladding, building paper, typical stud framing and insulation, and gypsum board. I am using measured driving rain and custom weather files.

The material (custom made material file from laboratory testing) does not contain Water Content values for upper levels of RH (>90%) within the MSF.
When MSF values are not manually estimated for the upper levels of RH , the water content of the cladding seems to be unrealistically high. It appears that the High RH experienced by interior side of the cladding (from diffusion) is causing the MSF to assume an extreme water content. This is mitigated when the MSF is manually estimated for higher levels of RH.

However, when the exterior paint layer (same material - kinda) of the middle and interior wood layer uses a manually estimated MSF , the water content of the observation also appears to be too high. When the MSF is not manually estimated ( automatically estimated in WUFI) than the water content of the observed layer seems more realistic. It appears that WUFI is using the liquid water being absorbed by the exterior layer to estimate RH of the element which is than transferred to the middle or observed layer.

I was wondering if someone may explain this phenomenon a little more in-depth. I can provide additional information if what I have written is unclear.
Many thanks in advance.

Regards,
Mark