Definition of Roof Flashing

Flashing is one of the most critical components of your roof because it works to prevent water from entering through holes in the waterproof membrane and between shingles. Flashing is also installed along the eaves and rake--slanted portion--of the roof to help shed water away from the walls, and may be installed during wall construction as well.

Definition

Flashing is typically made of very thin sheets of aluminum or steel, which are laid on top of the roof's waterproof membrane but below the shingling, then nailed or stapled into place. Flashing is typically found in the outer edges and valleys of the roof, around the chimney or other protruding pipes and vents and around dormer windows or skylights.

Types

Many contractors and do-it-yourself roofers prefer aluminum flashing because it is easier to bend and shape. Cutting and shaping roof flashing out of sheet steel is another popular contractor solution. You may also find flashing made of plastic, roofing felt, rubber or other metals such as copper. Roof flashing may come in pre-shaped units, which are often specifically designed for use with certain pipes or other protuberances, or in sheets which can be trimmed and shaped to fit your needs.

Considerations

Flashing must be sealed to prevent against the entry of water. While nailing or stapling the flashing will hold it down, a layer of glue, caulking or waterproof cement under the edges of the flashing is needed to seal it against intruding water. On a metal roof, the flashing can be soldered into place. Flashing is only the last-ditch defense in your struggle to keep water from penetrating the roof; there should also be a waterproof membrane in place as well as water-shedding shingles or other exterior roofing material.

Potential Problems

The most typical problems with roof flashing result from flashing that has rusted through or come loose. While these problems are relatively easy to fix--usually just replacing the piece of flashing or reattaching and re-sealing it will do the job--you must remember that working on a roof can be dangerous and, if the flashing has come loose and allowed water to penetrate into the roof's surface or below the waterproof roofing membrane, there may be other structural issues with the roof that you might not be aware of.

Specifications

Flashing can be made out of almost anything, but must satisfy several requirements to be truly useful. The most obvious of these is that it must be waterproof. Because corrosion is one of the most common problems with roof flashing, rust-proof material is highly desirable. Metal flashing should be thin enough to be easily shaped as necessary to fit roof contours. Finally, the flashing must be flexible enough to endure the typical expansion and contraction of roofing material as the house heats and cools, as well as exterior temperatures and conditions.