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Venting a cathedral roof with a dormer

mikebybee | Posted in General Questions on

Hey guys, I am doing a remodel on a 1940 bungalow.  It is a classic bungalow box,  1.5 stories with a storage attic.  I am looking at pulling off old roof, putting down lumber for a living space, then setting up the roof with 15″ parallel chord trusses, 10-12 pitch, plus a portion of the roof will have a shed doormer, 4-12 pitch.

I am thinking about setting up the air barrier on the bottom chord of the truss with 13″ of rockwool to get to R52, leaving 2″ for venting, then putting down sheathing and roofing over the top chord of the truss.

The walls will have 3.5″ rockwool inside the wall, then the air barrier exterior of the sheathing, then 3″ of rockwool on the exterior with a .75″ rainscreen then Hardi plank siding.

Question: Will the roof venting be adequate where it intersects with the doormer wall & rain screen?  Or, in those truss bays should I plan on closed-cell foam?

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  1. GBA Editor
    Martin Holladay | | #1

    There are products to address this situation -- for example, the Roof-2-Wall Vent by CorAvent.

  2. mikebybee | | #2

    Perfect thank you for the info

  3. Peter Yost | | #3

    HI Mike -

    interesting that you have chosen to go with 2-inch deep venting in your cathedral roof rather than just the 1-inch required by code; care to share why?

    I am just in the midst of doing "wingnut" testing of how soffit-to-ridge venting works and what factors affect air flow in vented cathedral roofs but have not yet tried 2-inch deep vents (see:

    Plan to do another GBA blog in the next month or two with an update on my testing.


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