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Sloped ceiling insulation with ventilation around dormer retrofit

here_to_learn_more | Posted in General Questions on

I’ve been reading through the site, and I’m wondering what one does for ventilation/insulation/air-sealing around a dormer.  Instead of insulating knee wall and lower ceiling, the preferred method seems to be insulating the sloped ceiling (roof rafters).  You can run site-built-ventilation-baffles 2″ below the roof sheathing, insulation like batts (below baffles), and a layer of rigid foam insulation over this and wood to prevent thermal bridging.  But, doing this from roof soffits to a dormer, the ventilation baffle would terminate at the dormer and not exhaust.  What does one do in this situation?  I envision one fix by putting the baffles an inch below the roof rafters, insulation below this, and rigid foam below (same layers but lower).  This could leave room for air movement from the rafters connecting to dormer to exhaust out of neighboring rafters going to the ridge vent.  Anyone have better ideas/suggestions?  Is there a standard?

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Replies

  1. Expert Member
    Malcolm Taylor | | #1

    There are a few ways to deal with discontinuous ventilation at dormers.
    - Choose an unvented assembly.
    - Install a continuous vent at the top of that section of roof where it meets the dormer wall.
    - You can strap the top of the rafters so there is some horizontal air movement between bays.
    - Use a variation on the above where the strapping is vertical and leave a gap at the dormer wall: https://www.greenbuildingadvisor.com/article/building-a-vaulted-high-performance-and-foam-free-roof-assembly

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