WUFI

Hi Calina and Joseph

I hope you are both well. I wasn't sure whether to post in this forum or the main one - no response as yet from main forum so trying you guys instead.

My question is about using foil backed materials.

I am using XPS Skin and Core from IBP database to represent Celotex as they have similar properties. However, as Celotex has foil both sides, I am selected the skin for one side, and was going to assign an Sd value for internal facing foil. Would this be correct, and should I select Metal Foil, or just vapour barrier? Or should I just insert another layer of XPS Skin to interior side?

Secondly, I want to then show effects of puncturing the internal facing vapour barrier (or skin/foil). But cannot remember how to do this! Is it within the Sinks/Sources menu?

Many thanks Nicole

Dear Nicole,

the extrusiun skin is not a foil but a more tight surface layer formed by the foam itself during the production process.

You can use both: a vapor barrier von both sides or an sd-value on the interior side.

I think, that it doesn't make much difference as the XPS is very vapor tight itself...

best wishes
Daniel

Hi Nicole
Re the quote from your mail below:
[quote=
Secondly, I want to then show effects of puncturing the internal facing vapour barrier (or skin/foil). But cannot remember how to do this! Is it within the Sinks/Sources menu?
[/quote]
In our hygrothermal simulations what we've found to be of great importance is the type of construction system the insulation is being applied to. If this system is timber frame then the vapour load from the room is the biggest moisture load and any reduction in vapour resistivity of the vapour barrier (be it a VCL or PIR or PH insulation board) could allow vapour penetrate into zone of the timber frame. However if the insulation is applied to single leaf masonry then the biggest moisture load is vapour (from water due to driving rain) from within the masonry substrate trying to dry to both sides of wall. In this case the gap will allow better drying to the room at this localised location only. Neither is a managed solution: moisture accumulation should be uniformly guarded against.

In my view you need to use WUFI 2D to analyse the discontinuity. We have done this once but need to return to the study. A sink/source will assume a continuous vapour or air ingress.

Hope that helps.