Will have a new project underway soon and would like to ask about my proposal for a modified insulation package
Will have a new project underway soon and would like to ask about my proposal for a modified insulation package. Just read Martin’s Musing on ‘Walls with Interior Rigid Foam” posted 3/27/15 and I have joined as a member of GBA today. Here is my description.
I would like to add and cover the interior side of wall stud framing with reflective foil, rigid insulation of likely 1/2″ thickness and the interior side of roof rafters with the same foil faced rigid insulation except at 2 inches thick for the roof. Thermax is one brand I am aware of at present. I would then strap (1 x 3) wall studs and roof rafters to receive sheetrock and or boarding of some type. This method seems to be ok for wall assembly but in Martin’s response to Steve of 4/2/15 he cautions against installing “interior rigid foam on an unvented cathedral ceiling” etc.
My cathedral ceiling proposed would be filled with the two types of foam in bays as described, which is basically an unvented cathedral roof. My understanding is with the foam insulation the venting is not possible nor is it required. My further understanding is that if the bays were to be insulated and filled with conventional fiberglass batts that venting ( proper vents, soffit & ridge vents ) must be used to keep the roof ‘cold’ and allow air to pass under the roof deck, thus venting the escaping ‘warm air or vapor’ from the roof assembly to the outside. I assume I did not misunderstand Martin’s response to say that if one adds 2″ of rigid foam to a cathedral ceiling at the interior side (with foam insulation in my case in all bays ) that one must ventilate that particular roof as is common with fiberglass cathedral roofs.
I note I have further homework as there is a further link…see How To Build an Insulated Cathedral Ceiling.
Thanks for considering my questions.
Kevin Begley, V.H. MA.
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