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rockies
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# Posted: 6 Aug 2017 06:39pm
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It would seem that filling your cathedral ceiling with insulating batts and then using baffles and eave/ridge vents to provide ventilation provides no benefits.
http://www.finehomebuilding.com/2017/07/11/roof-venting-doesnt-affect-cooling-loads
Esp important: the second last paragraph. Martin Holladay is one of the Senior editors at both Fine Homebuilding and the "Green Building Advisor" site.
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Steve_S
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# Posted: 6 Aug 2017 07:43pm
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That type of venting is NOT to cool the ceiling, it is moisture / humidity control, especially with Batts Fiberglass or Rock Wool. Spray Foam is it's own vapour barrier (like XPS, EPS & Poly-Iso) but PolyIso is better for ceilings.
Have a look at a badly vented Cathedral ceiling - filled with moulds & mildews, often black mould and if long enough like that saturation rot.
Only way to "cool the roof" is to prevent the heat from getting into it in the first place, there are different ways depending on your climate zone & general humidity levels.
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ICC
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# Posted: 6 Aug 2017 08:46pm - Edited by: ICC
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Cathedral ceilings bring many shortcomings when you consider energy efficiency. They can look grand but come with compromises. Flat ceilings make it easy to incorporate a conditioned space chase for keeping ducts, wiring, pipes, and the associated penetrations to the living space all on the conditioned side of the insulation. Then air sealed and super insulated above with an attic space with good soffit and ridge venting.
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toyota_mdt_tech
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# Posted: 6 Aug 2017 09:19pm
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I have a regular ceiling, insulated, and an un-insulated attic space, vents on each end, bird block vents at the end of all rafter tails, scorching hot outside, nice and cool inside. 
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