Framing a Dramatic Dormer
If doghouse dormers or shed dormers aren't dressy enough, A-dormers can add an exciting design note, and they're easier to seal against the elements.
Synopsis: A steep-sloped alternative to shed or doghouse dormers, A-dormers are built in the same plane as the exterior wall of the house below it. Here the author describes how he frames an A-dormer on a house that has three of them.
A lot of houses built on New England’s coast use dormers to tuck light, airy living spaces under their roofs. Steep-roofed A-dormers are an attractive approach to this style. A house my crew and I recently built on Block Island, Rhode Island, incorporated three A-dormers on the front of a conventional colonial-style roof.
An A-dormer differs from most other dormers in that its gable wall is built in the same plane as the exterior wall of the house below it. It’s just about the only dormer that looks good when not recessed into the roof. With steeply pitched roofs, A-dormers provide minimal floor area, but they can accommodate tall windows and interesting cathedral ceiling details. The exterior trim is usually simple with a uniform soffit width and long rakes connected by minimal lengths of horizontal fascia.
Because the entire A-dormer roof extends down to form a valley with the main roof of the house, none of the usual dormer details, such as cheeks, corner boards or siding-to-roof flashings, is an issue. Absence of these details makes A-dormers easy to finish and weatherproof.
As is the case with most other dormers, the main roof of the house is framed first: The gables are raised, the ridge beam is set, and the common rafters are installed with double or triple rafters framing the openings left for the dormers (“Cutting and Setting Common Rafters”). The dormers for this project were supported by 5-ft. high kneewalls that extend inward from the outside wall; in turn, beams in the ceiling below…