FAQ:General:HygricParametersofEcologicalInsulationMaterials

(11): Hygric Parameters of Ecological Insulation Materials

I want to investigate the hygric behavior of ecological insulation materials, such as flax, hemp or reed. However, these materials consist of fibres, whereas WUFI is mainly designed for capillary-active porous materials. What is the best approach?

The difference between fibres and porous mineral materials is in general not really crucial for the transport equations. The fibre materials may tend to have preferred transport directions, which would have to be allowed for by using appropriate material data for the x and y directions in a two-dimensional calculation.

Determining the liquid transport coefficients, however, may be difficult or even impossible if they change their consistency upon wetting (e.g. by caking).

On the other hand:
As long as your insulation materials don't become so wet that capillary conduction becomes predominant, you can ignore capillary transport and only consider diffusion transport. That is, you leave the liquid transport coefficients undefined and only enter a µ-value. Surface diffusion phenomena may be allowed for by using a moisture-dependent µ-value.

Since you probably only want to assess whether or not the insulation becomes wet by rain or condensation, you will mainly be concerned with water contents in the sorption moisture region of the moisture storage function, for which these simplifications should be adequate.
As these materials must be prevented from becoming wetted through anyway, there will be no need to investigate in detail the behavior of an insulation soaked full of water.