Drainage in a ventilated cavity

[David Lam]

Hi all

I'm attempting to model a ventilated cavity as accurately as I can.
I've read the useful information in the WUFI help and here: https://wufi.de/en/service/wufi-forum/? ... a5708d45cf

I have standard UK new building brick cavity wall. Liquid water will drain from the cavity at the bottom.
I am guessing that vapour can still track across the cavity, through the insulation and into the building.

As I understand it, I can either model it as per the link above, or remove the brick and cavity completely and simply put in an sd value in the surface transfer coefficients page, and turn the rain off.
Which one is more realistic bearing in mind liquid water will drain from the cavity?
Would I need to include a sink in the cavity?

Thank you
David.

[Daniel]

Dear David,

If you have a brick masonry which absorbs water and in the consequence leads to vapor drive towards the inside during sunshine after rain events, the simulation with a ventilated cavity is more realistic.

It is sufficient to consider the normal rain water absorpotion of the wall without additional sinks or sources in the cavity (apart from the air exchange source).

In masonry cavities the the average ventilation rates lies inbetween about 1 to 10 h-1.

best regards
Daniel