Roof Flashing

By Frank G. Ross

Residential roofing is typically composed of a variety of materials and surfaces whose main function is to keep out the various elements of weather. The most pervasive and difficult weather element to control is water. Roof flashing is a key feature of roof systems and one of the most important when it comes to preventing water penetration.  For the most part, the correct installation of flashing material is what determines whether or not a roof will leak.

Flashing is used to stop water from entering a home at its most vulnerable areas.  It forms the intersections and terminations of roofing systems and surfaces. The most common locations for roof flashing are at valleys, chimneys, roof penetrations, eaves, rakes, skylights, ridges, and at roof-to-wall intersections. Each of these different situations requires a different shape or type of flashing.  A few examples are step flashing, kick-out flashing, gutter apron flashing, valley flashing, vent pipe flashing and drip edge.

A sloped roof that meets a vertical wall (like the wall of a dormer window, or where a garage attaches to the two-story section of the house) requires special attention.  Step flashing protects the joints between the roof and vertical surfaces. It fits to each course of shingles and looks as if it is stepping up a wall or other surface. Though skylights sometimes have step flashing up the sides, they generally come with their own, integral flashing.

Water that travels down the step flashing toward the roof edge should be prevented from entering the wall system with a kick-out flashing.  A kick-out flashing, which hangs over the edge of the roof, diverts the water away from the wall and into the gutter.

 

Gutter apron flashing is similar to a drip edge.  It is placed under the shingles and over the back edge of the gutter to prevent water from running behind the gutters and rotting the fascia.

Valley flashing protects the valleys where two roof planes meet. This W-shaped channel is placed over the top of building felt before the roof's finishing material is installed.

Vent pipe flashing fits over flues and pipes. It is cone-shaped with a flange at the base, which is worked into the shingles as the roofing is applied. 

Drip edges are strips that run along the roof's eaves and rakes to prevent water from seeping under the roofing.

In general, properly installed flashing will function effectively. However, from time to time, the nails that fasten flashing may work loose, or the flashing material may pull away from seams and joints and require maintenance. 

Keep in mind that flashing details are a very technical aspect of roof construction, and installation or repair work is best left to experienced professionals. Even an inexperienced homeowner can keep a watchful eye out for potential problems, though. Make a point of checking the roof flashing and the condition of the shingles whenever the gutters are cleaned.  Ideally that would be every six months. Look for loose nails and any damage to the seals at the edges of the flashing. Check for exposed joints due to dried out roofing cement which has crumbled away. Also any badly corroded flashing will need to be replaced.

Frank Ross is a Certified Utah Home Inspector for Pillar to Post Professional Home Inspection and a full member of the National Association of Certified Home Inspectors and a member in good standing with the Utah Better Business Bureau.  Readers may contact Mr. Ross at (435) 867-6400 or frank.ross@pillartopost.com