Roofing: Shingles

Drip edges allow runoff coming down the roof to drip into the gutter; they also protect the raw edge of the roof sheathing. Make sure all drip edges are installed in the proper sequence. The drip edge at the eaves should be installed on top of the sheathing, so the roofing underlayment can then be layered over the drip edge. The drip edge at the rakes should be installed over the roofing underlayment. This installation sequence ensures that all roofing materials are overlapped shingle style.

Roofing underlayment protects the roof sheathing and framing from contact with water. If the roofing underlayment is installed correctly, water that penetrates the exterior roofing will drain out to the exterior and away from the home. Overlap the horizontal seams of the roofing underlayment 2” and the vertical seams 4”. Fasten the roofing underlayment with button cap nails a minimum of 6” on center for vertical and horizontal laps and 12” on center throughout the field. After the roofing underlayment is installed, it shouldn’t be left exposed to the elements.

Self-stick roofing underlayment, such as Grace Ice & Water Shield®, is an adhesive membrane material that’s adhered to the sheathing. In a cold climate, install self-stick roofing underlayment in place of standard roofing underlayment. The most important place for a self-stick roofing underlayment is at the eaves, where melted ice and snow will tend to refreeze. Because the membrane adheres to the sheathing, water can’t easily move behind it.

The exterior roofing doesn’t play a large role in preventing leaks at vent pipes, soil stacks, and other penetrations in the roof, so preformed flashing is installed to prevent water intrusion around penetrations. Cut the lower course of shingles to fit around the penetration. Then, install preformed flashing over the penetration, and set it in roofing tar. Fasten the flashing with roofing nails at the upper corners only. Continue installing the shingles above the penetration, making sure a full course of shingles overlaps the top of the preformed flashing.

Valleys are vulnerable to water intrusion because two roofs are directing water to a single point. For a closed-cut valley, install roofing underlayment on the lower roof first, extending it 36” past the valley. Then, install the roofing underlayment on the higher roof, once again extending it 36” beyond the valley. Once the roofing underlayment is installed, apply a piece self-stick flashing that's a minimum of 24" wide at the valley. Install the shingles in the same manner as the roofing underlayment. Afterward, cut the top layer of shingles 1" before the valley. By layering the roofing materials on the higher roof over those on the lower roof, water is directed into the valley and down the roof, instead of under the roofing materials.

There are two types of roof-to-wall intersections: roof rake-to-wall and shed roof-to-wall. At these intersections, extend the roofing underlayment up the wall surface a minimum of 12”. Install the roof-to-wall flashing at the intersection. Then, lap the housewrap or building paper on the wall over the vertical leg of the flashing, ensuring a continuous path for water to drain from the wall, down the roof, and to the gutters. To prevent the wall finish from wicking water, the finish should stop a minimum of 1 1/2” above the shingles. Keeping a reveal between the wall finish and the shingles is critical in managing water at roof-to-wall intersections.

Soffit vents allow air to enter the attic to ventilate the space. Soffit vents are required by code to prevent condensation, especially in colder climates. Install soffit vents continuously, rather than intermittently, so the air can flow uniformly into the attic space.

Baffles enable air to flow into the attic through the soffit vents. Attach baffles to the exterior faces of the top plates, so the attic insulation can completely cover the top plates. Also, maintain a 1" ventilation gap between the baffle and the roof sheathing. To keep blown insulation from falling into the ventilation gap, install the baffles so they extend up the roof interior at least 6" beyond the insulation level. In cold climates with wind-driven snow, it's best to install a preformed plastic baffle that prevents wind-driven snow from entering the attic, such as Berger Building Products' AccuVent™.

Shingles are installed in sheets, with tabs cut out along the bottom. The tabs are exposed to the weather; they provide the recognizable shingle pattern. At the eaves, install the starter course of shingles. Cut the shingles lengthwise, so the adhesive on the starter course is at the edge of the roof. Make sure the starter course overlaps the outer edge of the drip edge no more than ½". Install the first row of shingles, extending it no more than ½" over the outer edge of the drip edge. In high wind areas, code may require the starter course and first course to be flush with the outer edge of the drip edge. Layer the shingles from the eaves to the ridge. Nail the shingles per the manufacturer's specifications, typically four nails per shingle. At the ridge, install the ridge shingles, working from the ends of the ridge toward the center.

A ridge vent is installed at the ridge to ventilate the attic. There are two main types of ridge vents—metal ridge vents and shingle-over ridge vents. With a metal ridge vent, attic air flows freely into the vent and exits through a gap in the material. Wind-driven water is prevented from entering the vent and damaging vulnerable materials. With a shingle-over ridge vent, attic air enters the vent and travels through woven wire mesh to vent to the outside. This type of ridge vent is capable of preventing wind-driven rain and snow from entering the home. Ridge vents are preferred over off-ridge vents, since warm attic air will always rise to the highest point in the attic—the ridge.

A gutter is a trough at the roof’s edge that collects and channels bulk water away from the home. To keep bulk water from damaging the home, install gutters at all eaves. They should be installed 1” away from the exterior finish on any adjoining walls to capture runoff from the roof and properly drain it away from the home.