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= (13): Water-Repellent Facade =

How can I simulate a wall whose exterior surface has been treated with a
water-repellent agent? Is it correct to set the rain water absorption factor to zero?
Do I need to change the sd-value of the exterior surface, even though
I use a diffusion-permeable treatment?


The
[[Details:RainWaterAbsorptionFactor | rain water absorption factor]] must be
set to zero if the water absorption is indeed
completely stopped by the treatment. If water absorption is only reduced, you must
determine the
[[Details:LiquidTransportCoefficients | water absorption coefficient]] for
the treated material and replace the part of the wall which corresponds to the
penetration depth of the treatment with da layer of the treated material.


If the treatment does not change the
[[Details:WaterVaporDiffusion | diffusion permeability]] of the material, no
[[2D:Dialog_EditSurfaceCoefficients | sd-value]] needs to
be specified for the exterior surface. 
Many treatments do, however, increase the diffusion resistance factor (µ-value)
of the material. In these cases, this additional resistance should be allowed
for by an appropriate sd-value. Alternatively, and even better, you
can replace the part of the wall which corresponds to the penetration depth of the
treatment with a new layer that has the same material properties but an
appropriately increased µ-value.


Even if the water absorption is negligible (so that adjusting the rain absorption
factor instead of the liquid transport coefficients would be sufficient) and vapor
diffusion is not hindered by the treatment (so that no µ-value needs to be
adjusted), it might nevertheless be preferable to model the treated part of the
wall by defining a separate layer whose liquid transport coefficients have
been reduced or even set to zero.
This is because the capillary conduction in this layer does not only determine
the amount of absorbed rain water; it also influences the wall's drying behavior. 
Drying-out proceeds faster if water from the interior of the wall can be conducted
to the surface by capillary transport and can evaporate from there. Drying-out
is impeded, however, if capillary transport stops a few centimeters behind the
surface and moisture can only dry out after crossing this treated layer by vapor
diffusion. So this is another mechanism by which water-repellent treatment may
reduce the drying potential of a wall, in addition to a possibly increased
µ-value.

FAQ:General:WaterRepellentFacade - Versionsgeschichte

SebSta: hat „FAQ General:WaterRepellentFacade“ nach „FAQ:General:WaterRepellentFacade“ verschoben

Len: Die Seite wurde neu angelegt: = (13): Water-Repellent Facade = How can I simulate a wall whose exterior surface has been treated with a water-repellent agent? Is it correct to set the rain water...