cathedral ceiling/roof insulation

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Betty and Barry
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Joined: Thu Apr 11, 2019 5:57 pm

cathedral ceiling/roof insulation

Post by Betty and Barry » Thu Apr 11, 2019 6:08 pm

We are building a small winterized cottage on PEI, Canada. We would like to build cathedral ceilings. What is the best and cheapest way to insulate the roof, and how much R factor do we need to have? We are going to finish it with metal roofing.

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Re: cathedral ceiling/roof insulation

Post by Shannon » Thu Apr 11, 2019 9:58 pm

Well generally like most things "best " and "cheapest" don't work well together.
Cathedral ceilings are not the easiest to insulate properly using batt insulation .With batt insulation they also need to be ventilate properly between the bottom of sheathing and top of insulation.
I really would recommend using closed cell sprayfoam sprayed directly onto the underside of the roof sheathing. Being this is a small cabin your cost should be reasonable and this is one aspect I would splurge on a little anyways.

As far as R value that is not as easy of a question to answer anymore. With many places in Canada adopting the new energy efficacy rules. If your local municipality is using them there is a fairly particular way of figuring the RSI value for your entire structure based on the building materials use.
I used to be able to say spray it with 2-3" of closed cell foam or fill it with 7" of Roxul insulation and you would be fine but now it can be different. When you apply for your building permit you can ask what they require. If they are not following the new rules then my above comment would apply for most areas.
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