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What should I use on the exterior of a dormer?

user-6152174 | Posted in Energy Efficiency and Durability on

Climate code 5, old wood siding removed, 1/2″ fiberboard in place, no insulation in the 2 x 4 walls. I will be installing vinyl siding. Mostly concerned that the dormer breaths and drys properly and not concerned with adding any R value. Thank you for your time.

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  1. GBA Editor
    Martin Holladay | | #1

    If the room where the dormer is located is heated, you need to install insulation.

    Walls don't need to breathe.

    Building codes require, and building experts recommend, that your sheathing be covered with a water-resistive barrier (WRB) like asphalt felt or plastic housewrap before you install any siding. Make sure that the flashing at the base of your walls (where the dormer walls meet the roof) is in good shape and properly integrated with your roofing.

  2. Dana1 | | #2

    In zone 5 with fiberboard sheathing under vinyl siding you can fill the cavities with cellulose or fiberboard without inducing moisture problems. You can even use fan-fold XPS as a siding underlayment & WRB. and gain a double digit percentage thermal performance gain. (not that you were looking for that...)

  3. user-6152174 | | #3

    Thank you guys - I appreciate your help!!!

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