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What Is Roof Flashing? (2023 Guide)

Updated October 11, 2023

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Flashing is a critical part of any roof. It prevents leaks and keeps your home dry. Installing incorrectly can lead to serious problems such as water damage, mold and mildew, and weakened structural integrity. Our guide explains what roof flashing is and how it works, as well as average costs and how to hire a pro.

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What Is Roof Flashing?

Roof flashing is a thin strip of sheet metal installed around the edges and seams of roof features and penetrations, such as chimneys, vents, and flue pipes. Roof flashing redirects water away from seams and joists to keep it from entering your roof system and home. These are the roof areas that require flashing:

  • Roof valleys (low points where two slopes join)
  • Roof protrusions (windows, skylights, chimneys, vents)
  • Side walls and front walls
  • Roof edges

Roof flashing is usually installed over the underlayment and under the shingles on shingled roofs. It’s installed on top of the panels on metal roofs. When flashing isn’t installed correctly, it causes substantial damage that requires repair.

Roof Flashing Materials

Roof flashing is a flat, thin piece of metal that can be made from several materials. The best material for your home depends on factors such as climate and roof pitch. But according to Ken Byler, owner of Arizona-based Easy Roof Solutions, copper and aluminum flashing are generally considered the most durable and long-lasting options.

Here’s a look at each flashing material type and its strengths and weaknesses.  


Copper flashing is durable and one of the more expensive flashing materials. It’s highly resistant to corrosion, so it’s especially popular in regions with harsh weather. Although it doesn’t rust and has a long life span, copper fades into a green patina. Copper’s malleability makes it easy to solder and shape to fit any roof’s contours.


Similar to copper, aluminum is durable and able to withstand harsh weather. Aluminum is lightweight and low-cost, but the aluminum alloy found in flashing can pit and oxidize over time. It can corrode if left unpainted and exposed to salty air, wood, concrete, mortar, and other masonry materials.


Galvanized steel is the most common roof flashing material. It’s the cheapest but also the least durable type of metal flashing. It can’t typically withstand harsh weather conditions, contact with masonry materials (such as brick, concrete, or cement), or pressure-treated wood. Over time, the galvanized coating wears away and corrodes.


Lead is one of the oldest roof flashing materials. It’s also one of the longest-lasting, with a life span of over 200 years. Lead is soft and highly malleable, making it easy to bend and mold to the roof. However, lead must be managed and disposed of as a hazardous waste under the Resource Conservation and Recovery Act (RCRA) subtitle C requirements.

How Does Roof Flashing Work?

When rainwater or melted snow flows down the roof, it can pool in areas where the roof intersects with a vertical surface or changes slope. Contractors install roof flashing to redirect water away from these areas into gutters and drainage systems. Here’s how roof flashing works in roof installation.

  • A roofing professional will identify areas where roof flashing is necessary. These are areas vulnerable to roof leaks, such as skylights, vents, and chimneys.
  • Your chosen flashing material will depend on factors such as climate, budget, personal preferences, and local roofing codes and regulations.
  • The roofing contractor will cut the flashing to ensure it fits around each roof penetration.
  • The roofer installs flashing using nails or screws and shapes it to the roof’s contours.
  • The contractor uses roof sealant or cement to create a watertight seal between the flashing and the roof surface.
  • Multiple flashing layers are usually overlapped. This helps to direct water away from the roof and towards the gutters or downspouts.
  • The contractor inspects the installation to ensure the roof flashing is securely attached, watertight, and sloped for drainage.
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Types of Roof Flashing

The type of roof flashing used depends on its location and intended purpose. Here are the most common types of roof flashing.

Base Flashing

Base flashing is a waterproof layer installed over underlayment and underneath roof shingles. It prevents water damage where vertical walls intersect the roof deck.

Step Flashing

Step flashing is installed using L-shaped pieces. Each piece goes under the shingles and bends up against the vertical surface. This flashing type is partially visible, so some homeowners choose a material and color that matches the home’s exterior.

Counter Flashing

Placed above or opposite base flashing, counter flashing—also called cap flashing—is commonly layered on top of step flashing between the roof’s surface and chimney seams. While you can install counter flashing to an existing chimney, it’s best to handle during the chimney’s construction.

Chimney Flashing

Chimney flashing typically consists of two components: base flashing and counter flashing. It’s found at the base of a home’s chimney to prevent water from seeping in between the chimney and roof.

Drip Edge Flashing

Drip edge flashing is installed along the edges of a roof and acts as a barrier between the shingles and the roof’s edge. The purpose of drip edge flashing is to redirect water away from the roof’s eaves and into the gutters, preventing water from seeping into the roof decking or running down the sides.

Headwall Flashing

Contractors use headwall flashing, or apron flashing, at the point where the roof’s upper end meets a vertical headwall. It’s made from an L-shaped metal and custom-fit to the section of headwall.

Valley Flashing

Valley flashing directs water away from the intersection of two slopes. Water and melted ice easily collect here, but valley flashing helps guide it toward the gutters.

Gutter Apron Flashing

While very similar to drip edge flashing, gutter apron flashing is installed underneath the shingles and over the gutter’s back edge. It helps prevent water from getting behind the gutter and into the roof system by creating a barrier.

How Much Does Roof Flashing Cost?

Roof flashing repair costs an average of $200–$500, while replacement is $300–$1,500.* The price depends on the flashing material, the roof’s size and configuration, cleanup costs, and the extent of damage. Materials cost between $300 and $500, but the price can be as high as $1,500. Labor costs average $75 per hour but can range from $25–$100 per hour.

*Article cost data sourced from Angi and Fixr.

How To Hire a Pro

You may be tempted to install roof flashing yourself, but this job requires specialized knowledge and tools. Byler says it should always be completed by a licensed professional.

Here’s what to look for in a pro:

  • Ask friends and family for referrals and search online for a local roofing contractor.
  • Check ratings and reviews on sites such as Yelp, Trustpilot, and the Better Business Bureau (BBB). Keep an eye out for complaints and negative reviews. 
  • Ask for examples of previous work.
  • Check for licensing and insurance. You can also check with your state’s licensing board online.
  • Request multiple quotes and compare prices.
  • Get a cost breakdown and request a project timeline.

Our Conclusion

Roof insulation like flashing is vital to protect your roof from water damage. Without it, water can seep into the roof deck and inside your home, causing need for emergency roof leak repair. The high roof replacement cost from fixing water damage averages $3,447 but can range as high as $14,000. Hiring a professional contractor to properly install roof flashing can help to prevent these issues and save you money down the road.

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FAQ About Roof Flashing

What is the best type of roof flashing?

The best type of roof flashing depends on your budget, the required durability, and its visibility. People often prefer copper, but it may not fit everyone’s budget and fades into a green patina over time. Galvanized steel is cheaper but prone to corrosion in specific environments. It also oxidizes over time.

What happens if you don't have roof flashing?

If you don’t have roof flashing, water can leak between joists and seams into your roof deck. This causes structural damage and mold and mildew growth. Repairing water damage is expensive and time-consuming.

Can I install roof flashing myself?

Unless you’ve worked as a professional roofer, we don’t recommend installing roof flashing yourself. If you don’t know how to properly install flashing and ensure a watertight fit, your roof may be vulnerable to water leaks and damage. A professional roofing contractor will help you choose the correct flashing and materials to get the job done right.

Does flashing go under or over shingles?

Roof flashing can go over or under shingles depending on the flashing type and the roofing material. Flashing should overlap asphalt shingles, but for aesthetic purposes, flashing that extends over shingles is typically covered with additional tabs. On metal roofs, flashing is installed on top of the panels.

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