Easy Guide to Install Roof Flashing

Roof flashing is necessary element of roof building technique. They are installed whenever there is a change of materials, at the seams, or where a material is interrupted, at the places like openings. Flashing is usually made of metal. However, these days any waterproof material can be used to divert rainwater and can be described as flashing. Some of the common metals used for flashing are copper, aluminum, stainless steel, zinc and lead. Out of all these, copper is the popular choice since it is light and malleable.

Flashing is typically installed in thin strips of about 10 inches wide. Larger sheets would be susceptible to thermal expansion when applied to exterior surfaces. Flashing is installed with the upper layer overlapping so that water is always directed downward over an unsealed joint. There are many joints and seams, built into the average shingled roof that require a flashing. Flashing is also required at ridges, hips, valleys, and where there is a change in roof pitch, as in a gambrel. The steps listed below will explain the proper way to install metal flashing onto a typical asphalt shingled roof.

Ridges and Hips: One of the methods used to flash both ridges and hips uses flashing under the shingles that straddle the ridge (or hip). The flashing is cut into segments about a foot long and placed under each pair of shingles where they overlap.

Valleys: The open valley is a commonly used method of flashing. An unbroken strip of metal flashing 20 inches wide is nailed into the valley along its full length. The flashing should cover the same amount of roof on each side. Shingles are installed overlapping the flashing on each side so that a 6 inch strip along the central crease is left exposed. Take help from Commercial Roofers Austin for the installation of flashing in the valleys.

Exterior Wall and Roof Intersections: Flashing is required in places where a gable intersects with the exterior wall. It consists of short segments bent in half at a 90 degree angle. The segments are installed at the intersecting planes overlapping from above with one half turned up under the siding material and the other half inserted under the roof shingles.

Pipe Vents: Each pipe vent that projects through the roof has a pre-fabricated flashing component made of sheet metal 16 inches square. The cylindrical pipe penetrates the plane of the sheet metal at the angle of the roof pitch through an elliptical opening with a fitted collar. The sheet metal is inserted under the upper shingles, rests flat on the roof plane and overlaps the shingles below.

Chimneys and Dormers: Flashing at chimneys consists of a base flashing fitted into the shingles at each course, and stepped cap flashing installed onto the brickwork extending into the mortar joints. The base flashing and cap flashing are interwoven along the 2 sides. A solid continuous piece of cap flashing covers the lower edge or the front of the chimney and overlaps the base flashing resting on top of the shingles. The same pattern is used at the rear of the chimney, except that the base flashing is inserted up under the shingles. Dormers are flashed in the same way.