Quick Fire Questions on 'dry lining' a new build cavity wall

DavidHughes · Post by **DavidHughes** » Wed Dec 21, 2011 5:37 am -1100

How do you model the effect of the foil on a PU/PIR type board, do you put in figures for emmisivity, vapour resistance/Sd value or do you ignore the foil?

If board is fixed using dabs should you model the 20 mm or so 'cavity'

In the main unfilled cavity wall what is the typical air change rate for non filled cavities in cavity walls

If there is a mold problem with the warm leaf of the cavity wall is more venitlation to the cavity going to help? Is it possible to vary the air change rate until the Wufi Bio goes orange/green?

Hope the questions are still clear

Happy Holidays

Daniel · Post by **Daniel** » Wed Dec 21, 2011 8:53 pm -1100

Dear David,

you should consider the properties of the cover layer if its diffusion resistance is higher than the one of PU or PIR - the influence of a metal film on the radiation exchange over the air layer can be taken into account by adapting the effective heat and diffusion properties of the air layer (details you can find in the help).

The cavity can be modeled as stagnant air layer - ventilation you only get if you have openings to the indoor or outdoor climate. Is this intended? For venitlated air layers on the outside the n can vary between 10 and 200 h-1 depending on the size of the air gap and the openings... a higher ventilation rate with the exterior can improve the situation but does not always.

Daniel