# Cathedral Ceiling Vent-Barrier-Insulation Question



## Gary in WA (Mar 11, 2009)

Welcome to the forums!


I couldn't get your link to open.....

Does this cover it?: http://www.buildingscience.com/documents/published-articles/pa-crash-course-in-roof-venting

Gary


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## Windows on Wash (Aug 30, 2011)

DrMo said:


> Newbie Here...
> 
> I am retrofitting a ranch home in Michigan. Any comments on using a double layer of rigid foam board in a Cathedral Ceiling design as described in the link to the following article? -
> 
> ...


see above...


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## DrMo (Jan 8, 2012)

Thanks for both comments - so far - still would like to hear other thoughts as well...

Gary (GBR in WA) - I am sorry you could not get the link to open - it works for me... Perhaps if you copy and paste into your browser??? The article you provided does not seem to address my situation - not an attic or unvented cathedral roof. Thanks for your efforts! 

Windows on Wash - thanks for your detailed response! 

I don't know the exact roof pitch, but it is not an extreme slope, typical of a single-story ranch home - very easy to walk on. Good news - I have already installed my own hand-made strips - not the manufactured vent channels.

Can you tell me more about the "product that has the poly facing and skip the plastic" ? Is there a name brand? Finally, where can I purchase the acoustic sealant? Is there a name brand for that as well that you can recommend?

Thanks so much for your input! DrMo


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## shazapple (Jun 30, 2011)

Windows on Wash has it right. If you go with a thin enough rigid insulation it wont act as a vapour barrier, then you could fill the space with fiberglass and then cover everything with rigid insulation as WoW mentioned. Sometimes you can find (I haven't seen it around here) rigid with a plastic or foil face that acts as a vapour barrier, then you only need to tuck tape the seams. If you go with the 6mil polyethelene sheet, acoustical sealant is a terrible black sticky gooey stuff that will stick the perimeters of the sheet to most surfaces. It can be found at any big box store.


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## Sandhead (Nov 20, 2014)

How thin should the vented unfaced foam be?


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## Windows on Wash (Aug 30, 2011)

Its less a consideration of thickness as compared to facing on the foam. That is the more critical consideration. 

EPS is best if you are wanting to keep it vapor open.


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## Sandhead (Nov 20, 2014)

How about green guard extruded polystyrene foam from lowes?


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## Windows on Wash (Aug 30, 2011)

Check the facing on it and look up the perm rating.


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## Sandhead (Nov 20, 2014)

Unfaced Easy to cut and install
Meets all Type IV and Type X specifications. Perm is 1.5


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