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Recycled barn home - vented cathedral ceiling?

Zone 6A NE Pennsylvania. In the design stage of building a home from a restored barn frame. Ceiling will naturally be cathedral the roof system is a complete straight shot from the eves to top ridge. I would like to use recycled poly iso - if there is a better type please suggest. Start with a 1" air space between the 7" of poly iso and sheathing using "sticks". Poly iso would be placed between the 2x12 rafters. Then a 1-2" layer of closed cell spray foam bringing the R value to 49 or above.

I would then like to install brown board (wood that was originally on the roof to begin with) directly to the under side of the rafters creating the ceiling. Would this be an acceptable method of creating a vented roof system? Suggestions? Thanks for your time.

Asked by matt bowman
Posted Fri, 02/22/2013 - 22:21
Edited Fri, 02/22/2013 - 23:03

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3 Answers

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1.
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Matt,
Q. "Would this be an acceptable method of creating a vented roof system?"

A. Yes, although I advise you to increase the depth of your ventilation cavity from 1 inch to 1.5 inch or 2 inches. This type of roof doesn't really need ventilation -- but if you are going to include a ventilation channel, you might as well build it deep enough to work.

Answered by Martin Holladay, GBA Advisor
Posted Sat, 02/23/2013 - 06:17

2.
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Martin,
Thank you for the quick response. Would it be better to eliminate the ventilation cavity and place the poly iso directly against the sheathing? Is the way i am planning on finishing the ceiling okay?

Answered by matt bowman
Posted Sat, 02/23/2013 - 20:48

4.
Helpful? 0

Matt,
You can use any kind of boards you want for your ceiling, as long as your foam has been installed with attention to airtightness.

Rather than abandoning your plan for ventilation, here's another idea: install the 7 inches of rigid insulation under the rafters, in a continuous layer, instead of cutting the foam up into little rectangles that have to be carefully air sealed.

Answered by Martin Holladay, GBA Advisor
Posted Mon, 03/04/2013 - 13:54

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