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Community and Q&A

Attic ventilation with dormers

William Ridley | Posted in Energy Efficiency and Durability on

We live in zone 6a and our house has several dormers on the second floor. The dormers are what I call “face dormers”, in that they don’t have any vertical side walls, but just share the face wall with the side of the house, and have a long roof valley on each side.

Because of this design there is no opportunity for the soffit vents to pass air up into roof for the full width of the dormer. The dormer is framed such that the dormer ridge comes into a header that is the full width of the dormer at the eaves. Hopefully this description makes sense.

My question is, in the attic space in the main roof, just above these dormers where the header beam is, there is no flow of fresh air from the eaves, so does this create a dead spot that could warm up and cause snow melt/icing in winter? Is this a good area to consider spraying the underside of the roof with foam to insulate it?
WTR.

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Replies

  1. GBA Editor
    Martin Holladay | | #1

    William,
    Some roofs are easy to vent; some aren't.

    If a roof has dormers, valleys, hips, and skylights, it's impossible to vent each rafter bay from soffit to ridge.

    That doesn't mean that the roof assembly won't perform well. There are many "hot roof" designs that don't require venting.

  2. Chris Koehn | | #2

    William,
    One possibility for venting (required in some jurisdictions) is construction of a cold roof on top of existing framing and sheathing. Not inexpensive, but more affordable if accompanied by re-roofing. We have achieved this by installing strapping on top of the roof deck: ridge to eve on the main roof planes; parallel with dormer ridges, with free flow at the valleys. We either add a layer of sheathing, or install roofing directly over (as with metal).

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