Shingle roofs are popular, functional, and attractive. Installed correctly, they can last through their warranty period, typically 10 years, and beyond. Weather, particularly rain and snowmelt, is the biggest enemy of an incorrectly installed roofing system. For example, water leaking onto the sheathing causes rot. Water leaking into the attic wets the insulation and reduces its R-value. Water also encourages mold growth, which is bad for indoor air quality and, in extreme cases, causes structural damage to the attic framing. Water in the attic can leak onto ceiling drywall, causing leaks and water stains in the living space.
Although shingles drain much of the water that falls on a roof, shingles are not waterproof. Other roofing components, including the drainage plane, flashing, drip edges, and gutters work with the shingles to direct water down and away from the home.
Certain areas of a shingle roof are more vulnerable to water intrusion than others. These areas, such as valleys, ridges, gable ends, and roof-to-wall intersections, need to be constructed with additional attention and care.
Valleys
Install the roofing underlayment on the lower roof first. Beginning at the exterior edge, layer it shingle style up the roof. Extend the roofing underlayment 36” beyond the valley. Then, install the roofing underlayment on the higher roof, once again extending it 36” beyond the valley. Within the valley, install self-stick flashing that’s a minimum of 24” wide. Install the shingles in the same sequence as the underlayment. When laying the higher roof, extend the shingles 36” onto the lower roof. Cut the top layer of shingles 1” from the valley.
Ridges and gable ends
Install the roofing underlayment, layering it shingle style up the roof. The last course should overlap the ridge by 12”. Repeat on the other side of the roof. At the gable end, install the drip edge. Install shingles, shingle style, from the eaves to the ridge. At the ridge, install the ridge shingles working from the ends of the ridge toward the center.
Roof-to-wall intersections
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.
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