What Is Roof Flashing?

By Amanda Lutz Updated February 6, 2024

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Roof decking, underlayment (a fiber layer over the roof deck and under the shingles), and shingles all play an important role in protecting your roof and home from the elements. Roof flashing materials are installed in spots that need extra leak reinforcement to keep water out. Metal flashing is typically found in roof valleys and around features such as chimneys. Properly installing this flashing and ensuring it stays in good condition will help reduce your long-term roof repair expenses. We’ll explain the different types of flashing and how they work to keep your roof waterproof.



Understanding Roof Flashing

Flashing is a thin, corrosion-resistant sheet metal bent into shape to fit into a joint. Roof flashing helps direct water away from vulnerable areas. It’s generally made of galvanized steel, which is steel that has been coated with zinc to prevent rust. On shingle roofs, it’s installed between the underlayment and the shingles. On metal roofs, it’s usually installed on top of panels.



Why Is Roof Flashing Important?

Flashing is installed where roof leaks are prone to occur. This includes roof valleys, where two downward slopes meet. Roof penetrations—anywhere that a feature such as a chimney, plumbing vent, or skylight—should also have their seams covered with pieces of flashing.

Flashing serves one purpose: preventing water leaks and the ensuing water damage. Water that gets beneath roof shingles or other roofing materials can cause rot, mold, and mildew, and encourage pest infestation. Sealant is useful for small holes, but flashing provides waterproof coverage to a greater roof surface area. It’s also inexpensive and fairly easy to install.



Roof Flashing in Skylights and Shingles

Skylights provide natural light and improve the look of a room, but a roof window is notoriously difficult to waterproof. To install a skylight, a roofing professional must cut through shingles, underlayment, and decking. No matter how well the skylight fits into the resulting hole, its perimeter will always be prone to leaks. Most skylights have a frame that protrudes slightly from the roof plane, allowing installers to nail flashing around the frame’s edge. The cost of installing a skylight includes flashing installation.



Different Types of Roof Flashing

These are the most common flashing types you’ll encounter during a roofing project.

Apron or Continuous Flashing

Also known as apron flashing, continuous flashing is a single piece of metal that runs the entire length of the joint being waterproofed. It’s often used where dormers or other protrusions meet a roof’s surface. The advantage of using a single metal strip is that there are no joints or overlaps that could leak. However, a single piece of metal can’t expand and contract with changing exterior temperatures, meaning it could break or warp over time.

Step Flashing

Step flashing solves this problem by lining a joint with multiple pieces of flashing that overlap like fish scales. This flashing consists of rectangles of sheet metal bent into an L-shape. The base of each L is nailed to the roof, and the top is secured to the vertical wall of the dormer, chimney, or other protrusion.

Base and Counter Flashing

These two flashing types are used together as pieces of a set to protect hard-to-waterproof features such as chimneys. The base flashing is typically a continuous L-shaped piece that attaches to the roof, but its upper edge is not attached to the roof penetration that it rests against. The counter flashing piece is attached to the penetration but not to the roof, so the pieces of flashing overlap but are not secured to each other. Flashing that’s visible on a roof is usually counter-flashing. This system of base and counter flashing allows for extra expansion and contraction without damage, which is especially important in areas that are difficult to waterproof, such as chimneys.

Drip Edge Flashing

Various flashing shapes are installed at the roof’s edge to prevent precipitation from running down the fascia boards and into the soffits. The simplest is an L-shape, similar to other flashing types. However, there is also T-shaped and F-shaped drip-edge flashing, which are slightly more expensive but can also be more effective at directing water into gutters.

Valley Flashing

This type of flashing acts as a V-shaped channel for water that runs into the areas where two roof slopes meet. Since so much rainwater passes through this area, it requires extra protection. Valley flashing can be hidden under shingles or left exposed in open valleys. It can also be one piece of continuous flashing or several overlapping pieces, such as step flashing.

Pipe Flashing

Pipe flashing resembles a one-piece collar that fits around a pipe’s diameter. Unlike other roof flashing types, it’s sometimes made of rubber or silicone instead of metal for easier expansion and contraction.

Wall Flashing

The area where the roof meets an exterior wall is typically lined or covered with wall flashing to provide extra waterproofing.



Flashing Materials

Roof flashing is typically made of metal, but there are several metal flashing types to choose from.



Professional vs. DIY Roof Flashing

While flashing is easy to install, it’s only the middle step in a larger roof replacement process. A home’s roofing system is a complex feature, and incorrectly installing the flashing can shorten a roof’s life span and risk water damage. Thus, we strongly recommend hiring a licensed roofing contractor to install or repair flashing. Shingle roof pricing will include flashing as part of the total cost, so homeowners won’t have to install it themselves.



Signs You Need Roof Flashing Replacement

Here are some signs that your roof’s flashing needs to be repaired or replaced.



Roof Flashing Maintenance

After your roof is about five years old, having an annual professional inspection is a good idea. It ensures flashing, and other materials are still in good condition. If there are any problems, a knowledgeable roofer can fix them before they can cause widespread damage.

Other common-sense forms of roof maintenance can also help protect your flashing. Ensure your roof remains debris-free and that gutters stay clear and in good condition. Gutter repair expenses are low compared to the cost of fixing a water-damaged roof.



Our Recommendation

Roof flashing is simple metal sheeting that covers your roof’s joints, but it plays an important role in preventing leaks and water damage. If you invest in corrosion-resistant flashing materials, you typically won’t have to worry about rust or damage. However, flashing can crack or break over time and may need to be replaced.

We highly recommend hiring a licensed professional to inspect and replace your roof flashing. If it’s time to replace your roof entirely, flashing will be one small part of a new roof’s cost.



Roof Flashing FAQ

Is flashing necessary on a roof?

Roof flashing protects your roof’s structure and stops water leaks and damage.

What does flashing on a roof look like?

Flashing is a thin sheet metal typically installed against roof decking. However, it may be visible as stairstep-like metal rectangles against the sides of chimneys and u003ca href=u0022https://www.architecturaldigest.com/reviews/home-improvement/cost-to-add-dormeru0022u003edormersu003c/au003e.

What happens if you don’t have roof flashing?

If your roof’s flashing is deteriorating, cracked, or absent, rainwater will leak underneath shingles, between roof joints, and into your attic and home.

What is the purpose of flashing?

Flashing lines the joints between structural features, such as roof slopes, to shore up weak spots by directing water away.