Foil faced Polyisocyanurate insulation

Russ · Post by **Russ** » Sat Apr 24, 2010 6:28 am -1100

would I be able to get some help ?

I have been asked about the use of foil faced polyiso insulation and am trying to incorporate this into a wall system model that includes this foil faced polyiso, air barrier, exterior gypsum, batt insulation, interior poly vapour barrier and interior gypsum. Outside of the polyiso is a 1" air space and brick. I am asking what is the best way to incorporate this into the model ? With this wall make up I would expect there to be an issue since there is a double vapour barrier. To try and model this initially, I had tried using a poly vapour barrier and the regular polyiso that is in the materials list, but when I run the simulation, it seems to work. I tried the same simulation without the interior vapour barrier and this actually seemed to be worse. The climate is a cold climate.

Any suggestions or help would be appreciated.

Thanks,

Russ

Achilles Karagiozis · Tue May 04, 2010 1:47 am -1100

Double vapor retarders sometimes seem to work, but in real life you never have a perfect scenario where only vapor diffusion occurs. Thus you should always test your structure for some water ingress.... that is where you see the catastrophic effects of double vapor retarders. By using a vapor impermeable membrane as a substitute for foil facing is appropriate, as long as the perm rating of the foil is equivalent (ie... no foil perforations). Cavity ventilation while a great element in many walls, in your case will impact the construction in a minimal manner. Have you investigated the use of a vapor retarder that changes as a function of RH ?.

Russ · Post by **Russ** » Thu May 06, 2010 1:53 am -1100

Thanks very much Achilles

TSkopic · Post by **TSkopic** » Fri May 02, 2014 1:09 am -1100

Hopefully this will be handled as a question and not a reply.

In the North American database, how do you add foil to Poly-iso insulation? The best that i could come up with was adding vinyl wallcovering in lieu of foil, but hope you have a better suggestion.

Anais · Post by **Anais** » Wed Nov 25, 2015 2:32 am -1100

Hi,

So at the end how did you model it ?

I use the "polyisocyanurate insulation" from the NA database with 2 layers of vapour retarders (sd=1500) around to simulate the aluminium foil - couldn't find any aluminium in the databases.

If you have a better way to model it, I am interested

Anais

WUFI