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Do dormer windows require strapping under rough faced channel cedar siding?

Socold | Posted in General Questions on
Our house has rough faced channel cedar siding installed vertically on the exterior walls, with strapping placed over black fibrous boards underneath.
There is a flat dormer window that protrudes from the ridge line of the roof. The dormer has the same siding on its walls, but it is directly layered over plywood sheeting with only roof felt paper in between. 
There is no strapping present.
It is generally recommended to use strapping on exterior walls to create an air space between the sheeting and the siding. Does this recommendation apply to dormers as well?
We are currently having our roof replaced and would like to know if it would be advisable to add strapping to the dormer. We would, of course, ensure proper shingle overhang.
We live in Canada, and our house was built in 1987.
Thank you.

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  1. Expert Member


    A gap between the sheathing and the siding is always a good idea in Canadian climates, and dormers without overhangs are particularly susceptible to moisture problems. With horizontal strapping you won't get the benefit of a ventilated gap or drainage plane, but it still:

    - Protects the sheathing from any water that gets through the siding
    - Allows the siding to dry better
    - Allows the dormer walls to dry to the outside

    I would definitely include strapping under the siding.

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