What Is Roof Flashing, and How Does It Work?

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Roof flashing is pieces of sheet metal, galvanized steel or aluminum. This component keeps water leaks from occurring in roofing systems. Contractors install flashing in the parts of the roofs and exterior walls that are vulnerable to leaks, such as roof valleys, chimneys and the intersection between a dormer wall and the roof surface.

You need to make sure your roofer installs the flashing correctly because when this component is faulty, leaks will most likely occur. When installed properly, flashing works with gravity to help ensure rainwater is diverted safely to the ground.

Flashing is material that is used to direct rainwater and other precipitation away from the roof and into gutters or off the roof. Flashing plays a vital role in maintaining the integrity of your roof. There are areas of your roof that are prone to leaks. These are generally areas where water collects, such as valleys where two roof slopes meet. Places where the roof meets another structure are also prone to leaks at their joints. Because of this, flashing is installed almost anywhere a roof joins another structure, such as a chimney, dormer, skylight, or vent.

Flashing protects your roof from leaks by adding another layer of material specifically designed to redirect water. Without flashing, or when flashing is damaged or deteriorating, the risk of leaks increases greatly. Leaks can have a cascading effect on homes, causing large amounts of damage well beyond the roof. If a leak is not noticed and fixed immediately, a home can experience water damage.

Damage from Leaks

A leak into an attic space can cause moisture to build up and seep into the wooden structure. This may weaken the structure and even cause it to begin to rot, causing further structural damage. This can require expensive repairs that involve hiring a contractor to remove and rebuild parts of your house’s basic framing.

Other water damage occurs when water comes in contact with drywall in a ceiling or wall of your home. Drywall soaks up water and can become waterlogged. Wet drywall creates a number of hazards. The wet drywall can serve as a breeding ground for mold and fungi. When spores form these molds and fungi are released into the air they can make people in the house sick. Removing such growths is not always easy. A water damage specialist will start by spraying some form of poison on the mold or fungus to kill it. After that, the section of drywall affected by the mold may have to be removed and replaced. If there is too much moisture in the area, the area may have to be sealed off and treated for days or weeks with a dehumidifier.

How Do You Know if There Is Flashing Damage?

Rust

Roof flashing can still corrode over time even if it comes with galvanized coatings. If the flashing already has rust, it will no longer protect the components of your roof against water penetration. It would need cleaning, sealing or a replacement.

Holes

It only takes a small hole for water to seep beneath roofing shingles. Small animals can also create tiny holes in your roof, which could allow water penetration. Flashing with holes would need to be sealed before they cause major issues, such as leaks.

Cracks, Dents and Bends

Cracks and dents on metals break the galvanized coating on steel. Once the flashing has been compromised, it would be more prone to rusting.

Missing Parts

High winds and extreme weather events can loosen the flashing on your roof. Repairs and replacements must be performed immediately if there are missing flashing pieces.

Leaks Inside Your Home

Signs of flashing damage can also be apparent inside your home. Check areas near your fireplace, windows and skylights for water leaks. Leaks can also occur in your attic due to flashing failure.

Damaged Shingle or Siding

Your siding can suffer from damage if the flashing does not shed water properly from the roof. You may notice signs of water damage on shingles in low spots of areas near flashing, such as bending and darkening.

Mold or Stains on Fascia Boards

When a contractor fails to install the drip edge flashing incorrectly, mold and water stains can develop on fascia boards.

Types of Flashing

There are many types of flashing, but they all fall into a few broad categories. Materials used for flashing vary. By far the most common material is sheet metal. Roofers usually use galvanized steel for its durability. In some cases aluminum may be preferable since aluminum is more easily bent and easier to work with. In some specific situations a roofer may use copper flashing. It is most common on historic homes or homes with unique roofing materials, including roofs made completely of copper.

Another material that can be used for flashing it PVC plastic. This material is cheaper than metal and easier to cut and work with. However, it is not as durable. When exposed to sunlight over a long period, PVC plastic tends to break down. With PVC plastic flashing it may be necessary to monitor the condition of your flashing and repair or replace it as it deteriorates.

Some flashing is now available made of synthetic materials and composites. These materials are relatively new and have different properties. Often they are used for their durability or ease of installation.

Where Flashing is Installed

How flashing is installed depends on where it is installed. The most basic type of flashing is the flashing that collects water in the valleys of your roof. These are the joints where two slopes meet. Flashing in these areas will be installed underneath the shingles on either side. When water reaches the valley it will flow off the shingles and into the gulley created by the flashing. From there the water is safely directed to a gutter, downspout, or simply off the edge of the roof.

Chimney Flashing

Another common location for flashing is around a chimney. Chimney flashing is actually a collection of several types of flashing. Continuous flashing, a single strip of metal (or another material) is installed along the base of the chimney where it meets the roof. Along the sides of the chimney, step flashing is installed. This consists of squares of flashing that overlap, similar to shingles, and climb up the side of the chimney along with the slope of the roof.

Saddle flashing is like a little mini roof behind the chimney on the higher side. Also called a cricket, this is a ridged design feature. It directs water and debris to either side of the chimney. That way it does not backup and collect on the high side of the chimney.

Finally, where the top of the flashing meets the brick (or other material) of the chimney, cap flashing will be mortared or caulked to the chimney. This flashing is attached to the chimney at its top and its lower part overlaps the flashing below. The bottom edge of the cap flashing is molded to direct water outward and away from the step flashing. It keeps water from seeping behind the step flashing.

Other Locations for Flashing

Flashing is also used around vents in the roof. The type of flashing depends of the type of vent. This flashing is also commonly included with the vent hardware. The same is true of skylights. Skylights require flashing around the area where they meet the roof. The flashing is often integrated into the design of the skylight. If it is not, flashing must be installed to prevent leaks around the skylight.

If a house has dormers, flashing will be required where the vertical walls of the dormer meet the sloped roof. Like with a chimney, stepped flashing is installed along the vertical wall of the dormer following the slope of the roof. The step flashing will be capped with cap flashing that is attached to the exterior of the dormer. The base of the dormer will get continuous flashing and the peak of the dormer will get saddle flashing. The area where the roof of the dormer meets the rest of the roof will be treated like other valleys, with standard flashing that rests beneath the shingles on either side.

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