How to Install Siding on Dormers

Preparing the Dormer

• 1

  Bend and trim flashing so that half is on the dormer side and half on the roof. Nail in place around all three sides of the dormer. Caulk the nail holes and around all the edges of the flashing.

• 2

  Attach one piece of J-mold at the roofline on the angled sides of the dormer and another piece on the roofline.

• 3

  Install siding corner pieces at the front of the dormer, going under the eaves on the roofline to the peak of the gable. Angle the cut at the back of the corner pieces for the tightest fit under the eaves.

Creating a Template

• 4

  Cut a piece of siding so it is a little longer than the side of the dormer. Hold it along the side of the dormer, approximately halfway up (exactly where does not matter). Make certain that the bottom corner is against the roofline, inside the J-mold. Use a level to be sure it is straight, and nail lightly in place.

• 5

  Take another piece of siding, and hold it along the angled roof line, covering the first piece of siding. Draw a line with a pencil on the first piece showing the angle where the second piece covers it.

• 6

  Remove both pieces of siding. Use a saw to cut along the line you have made. Use this as a template for the roofline angle for all the pieces of siding you install on the dormer.

Installing the Siding

• 7

  Measure for the first piece of siding on one side of the dormer. You will work from the bottom up. Use the template to draw the angle on the piece, and then cut. Push the bottom edge under the J-mold, and nail in place, being careful not to push the nails all the way in. Leave about 1/8 inch of the nail showing.

• 8

  Repeat the measuring and cutting for the remaining side of the dormer, continuing to use the piece you have cut as a template for the angle. Trim the final piece to fit under the J-mold at the eave.

• 9

  Repeat the process for the other side of the dormer.

Siding the Gable End

• 10

  Cut the siding to the width of the gable end of the dormer, and nail the bottom piece in place. Move up, checking that each piece is level, and go around the dormer window.

• 11

  Measure the pieces carefully as you move up the gable, tucking the corners under the corner pieces already in place before nailing them down. Tuck the final piece under the peak of the gable and secure.

• 12

  Add trim to the edges of the window and the corners of the dormer to cover the siding. Caulk around all the trim.