Building an Eyebrow Dormer

Ryan and Mike Dangelo, of M.J. Construction, in Centerville, Mass., framed the garage walls and roof, headering off a rectangular opening in the roof for the eyebrow dormer.

The window trim layer was then nailed into place.

Because strength was not a concern, the subfascia layer was cut from 2x12 dimensional lumber.

A rabbet routed in the lower edge of the subfascia allows it to lap over the window trim.

The fascia layers extended past the window trim with space left below for shingles. The final layer of fascia would be installed after the roof was sheathed.

The author also printed out patterns for the dormer roof sheathing, which was cut from 1/4-inch plywood.

The pieces of sheathing needed some minor tweaking with a jigsaw to sit just right.

Ryan ran red-cedar shingles as a starter course on the dormer. Asphalt shingles were then woven across the valleys.

The author decided to frame the dormer roof with LVL "ribs." Using a CAD program and a plotter, he printed out patterns of the ribs for the carpenters.

A 2x4, cut at a 45-degree angle and tacked to the roof, held the first rib in position for nailing.

The ribs were spaced 10 1/2 inches on-center with 2x6 blocks cut at a plumb angle for a 4/12 pitch. A furring strip tacked to the roof and to the first rib held the first rib in position while the other ribs were being installed.

The second and third ribs required three spacer blocks each, two at the sides and one at the top. The small top rib needed only one 2x4 spacer.

Ryan covered the face of the framed dormer with heavy felt paper and extended it down the roof to be woven into the roofing underlayment. Next he angled a length of lead flashing over the bottom of the window opening and extended it about 4 inches onto the garage roof. The window was then installed, with the curved flange caulked to the rib opening before it was nailed. Finally, peel-and-stick membrane covered the rib and lapped down over the flange as well as over the lead flashing on the sides of the window.

The window trim was cut from 3/4-inch PVC. Ryan started with the wider piece of fascia trim, and used it as a guide to cut the curve on the second piece of trim.

A belt sander was used to smooth the inside curve of the PVC window trim. This piece would be installed last, once the dormer roof had been sheathed.

The layers of window trim were dry-fit on the ground first.

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