# Venting cathedral ceiling metal roof



## Natef350 (Mar 13, 2016)

Hi guys new to the forum, just a small town guy trying to get by. Most my roofing has consisted of re-roofs but I have an addition I'm doing and looking for advice as I haven't done a cathedral stick built before. Its a 10/12 pitch, stick built, 2x12 rafters cathedral ceiling. Plan is from inside out is, 5/8" T&G, vapor barrier, R38 fiberglass(trying to go spray foam instead), 5/8 osb, 1" blue board sort of a thermal break, vapor barrier, strip it and then standing seam. I'm in western pa I'm concerned with venting between the metal roof and blue board. Do I need to? I was going to bulk head off where the rafter sit on the wall, put vented soffit on and use a hole saw to drill every so far so it could pull air up through between the metal and vapor barrier/foam.


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## Randy Bush (Oct 23, 2014)

I have never did anything this way even though have done a lot of metal roofs. Will R38 be cavity fill on the 2x12? I think ventilation is need but just a little different then you are thinking. I am no expert and is only my thoughts, But I think it should be more like this. on top of 2x12 1/2 sheeting blue board, stripping running same as 2x12 then 5/8 sheeting, thinking that will provide venting, underlayment, not a second vapor barrier, then standing seam. 
I believe it is better for the metal to be on a flat deck then on stripping. No chance of moisture build up like could happen with stripping running horizonal. 

I would try to find a engineer to maybe give more advise on this if you can.


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## shazapple (Dec 3, 2010)

I would purchase engineered trusses that provide enough space for R60 fiberglass insulation and foam ventilation baffles under the deck, then underlay, strapping, and metal roof on top of the deck. It would probably be similar cost to what you propose and you don't have to worry about enlarged fascias, double vapour barrier, or etc.


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## Randy Bush (Oct 23, 2014)

I believe the op is talking about a house already built with the need of a new roof. Therefore using a truss on it is not in the plan. Unless this was a pole building which it is not I don't see the benefit of using strapping. A solid deck I believe is still a better way to go and cost little if any more to do . Gaining ventilation is the main concern it seems the op was after.


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## Natef350 (Mar 13, 2016)

Trusses are not an option, my main concern is venting between the metal and deck due to condensation. I can screw the metal to a flat deck but wouldn't that limit air flow creating a better chance for condensation? That why I was going stripping to raise it up.


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## Randy Bush (Oct 23, 2014)

What do you have for venting on the roof now? If that is ok then there is no need to vent between the deck and metal , put down a roofing underlayment and go. I still believe the way I suggested would work.


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## hanerykroze (Mar 29, 2016)

*Venting can consider during when vapors impervious metals are installed under the slab, when flooring manufacture needs.
*


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## Silb (Mar 23, 2017)

You'd need to be careful working in an old building like that


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