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Insulating a cathedral ceiling

I live in an early Lindell cedar kit home. I shan't go into the construction method but it is far from conventional. I need to add insulation and also re- roof. I was thinking of stripping the roofing and sheathing, laying down either 2x4 or 2x6 rafters, filling the bays with Thermax insulation, sheathing and re-roofing. My question is if the rafter bay is not completely filled do I absolutely have to vent the bays. I understand that the reflective coating of the Thermax is only effective when used with an air gap, but to vent the roof, because of the original construction method, would be a total pain in the behind. Any and all ideas will be greatly appreciated.
Thanks ....Dave.

Asked by Dave Hodges
Posted Jan 17, 2013 6:27 PM ET
Edited Jan 17, 2013 7:04 PM ET

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2 Answers

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Dave,
It makes sense to add rigid foam on top of your existing roof sheathing if you are re-roofing. You don't need ventilation channels, as long as you install enough foam. And you don't need 2x4 or 2x6 rafters -- all you need is a thick layer (or two layers) of rigid foam, followed by a layer of plywood on top of the foam.

As an alternative, you can use a product called nailbase. (Google it.)

More information here: How to Build an Insulated Cathedral Ceiling.

Answered by Martin Holladay, GBA Advisor
Posted Jan 17, 2013 6:49 PM ET

2.
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I agree to what dave said you can use rigid foam for re-roofing and also the article given is very useful for us to understand how to build insulated cathedral ceiling.

Answered by Greg Pittman
Posted Jan 18, 2013 6:16 AM ET

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