A dormer is like a small room set into a roof. It has its own roof and three walls that jut out from the house roof. A typical dormer has one or more windows on the front and side walls that are framed much like house walls, with top and bottom plates and vertical studs. Dormer roofs normally are covered with the same type of roofing as the house. Walls may be finished with siding to match the house or shingles to match the roof. Shingle techniques will vary with the type, but the basics are the same.
Things You'll Need
Level or plumb bob
Shingles, type varies
Corrosion-resistant shingle nails
Utility knife or saw
Install metal flashing at all wall-roof intersections and around windows. Fasten a vertical side of flashing to the wall with galvanized flashing nails and a hammer and lay the other side flat on the roof. Put flashing up the sides of the two walls and across the bottom of the front wall. Set flashing around windows with one side against the wall, the other inside the window framing.
Put a housewrap membrane over the dormer walls and roof intersections. Fasten this in place with a construction stapler. Seal edges around a window with tape complementary to the type of housewrap. Staple roofing paper over the housewrap if the shingle manufacturer specifications call for it.
Shingle the house roof around the dormer first, so shingles on dormer walls will cover the edge where the roof shingle abuts the wall. Use a level or plumb bob to snap a vertical line one shingle width inside a dormer corner, as a guide to keep shingles straight up the wall.
Lay the bottom course of shingles first, starting with the front wall. Put on a starter course of shingles the width of the wall, leaving a 3/4-inch gap above the roof at the bottom. Nail shingles through the top of each shingle; the number of nails will depend on the type and size of the shingle so check recommendations of the supplier. Use corrosion-resistant nails and drive the heads flush with the shingle.
Add a second course of shingles on top of the first layer, but with the shingle bottoms extending down to about 1/2-inch above the roof. Start a second course or layer with a half-width shingle, so the vertical seams do not align. Overlap shingles from the top by about half a shingle length. Keep the bottom of the row straight.
Cut shingles to fit around the window opening, both horizontally and vertically. Trim shingles with a utility knife or saw; most types of shingle can be snapped apart after first marking a deep cut line with a utility knife. Put shingles around windows before the outside finish trim is added.
Snap a horizontal chalk line about shingle height on the side walls, where the roof intersections slope. Set the top of a shingle level with this line and mark the bottom for the angle of the roof. Cut the bottom to that angle and nail the shingle in place, butted up against the edge of the front wall shingle. Trim individual shingles to the slope of the roof and install a first course to the end of the wall.
Install a second bottom course like the first, trimming shingles to the slope. Begin a second full course with a half-shingle and add courses up to the roof line; shingles should not need trimming on additional courses until the roof line. Trim shingles on the top course to run right to the bottom of the roof framing.
Finish dormer wall shingles with wood trim, typically 1-by-4-inch boards. Put trim on both dormer corners to cover shingle ends on both sides, along the wall tops where they meet the roof and around a window. Nail trim with corrosion-resistant nails through the shingles into the dormer framing.
Adapt the installation technique to the type of shingle. Cedar or other wood or fiber cement shingles are installed as separate shingles. Metal shingle tiles are similar to cedar or wood, but must be cut with tin snips or metal saws. Asphalt or composition shingles may be either individual shingles or three-tab wide shingles.