Cathedral Ceiling Vent-Barrier-Insulation Question
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? -
I appreciate any comments as I have a very similar situation - I am using 2" rigid foam board with a 1" vent channel from eaves to ridge between every rafter. Then I plan to add batting below the foam.
I am wondering about if/how to seal the joints and seams around the foam board and whether to add more rigid foam board below - and/or a plastic vapor barrier.
I am concerned about the possibility of creating a "vapor sandwich" between the bottom layer of foam and/or plastic and the top layer of foam, with batting in-between.
Additionally, would there be any problem with adding multiple layers of rigid foam directly on top of one another? Would this create a possibility of condensation in-between?
Finally, in using a plastic barrier, what products should I use to seal the overlaps and outer edges?
thanks for your comments! DrMo
Welcome to the forums!
I couldn't get your link to open.....
Does this cover it?: http://www.buildingscience.com/docum...n-roof-venting
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
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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