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Dormers – Exterior Insulation Details

user-7523812 | Posted in General Questions on

My historic 1.5 story farmhouse in Northern Vermont has 3 doghouse dormers with no insulation.  I’m replacing some rotted boards and reroofing.  I’d like to add rigid insulation on the exterior of the dormers.  I will have to build up the dormer roof to extend it over the rigid insulation on the dormer walls.  I’m wondering if anyone has any good details insulating and flashing a dormer from the outside?   

Please note  – I can add rigid insulation to the top of the dormer roof and walls.  However, I am not adding exterior insulation to the entire roof of the house at this time.  I couldn’t find a contractor to do it and the roof is leaking now.

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  1. Expert Member
    Akos | | #1

    I would add your rigid insulation than install your house wrap over this. From that point, the flashing details are the same as standard construction, just flash to this layer.

    You'll also need plywood over the insulation on the roof for the shingles.

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