What is Flashing on a Roof & Why is It Important?

Roof flashing is a critical component of any roofing system, and without it, water could easily penetrate your roof and cause significant damage to the structure underneath. It’s a thin piece of metal, typically made from pre-finished aluminum or steel, installed along the edges of a roof where it meets the wall, where two slopes meet, and around protrusions like vents and skylights.

What is the Purpose of Flashing on a Roof?

Roof flashing protects the vulnerable joints and seams on a roof from moisture penetration. When properly installed, it effectively redirects water away from vulnerable areas, helping to prevent leaks and other issues.

Is Flashing Necessary on a Roof?

Flashing is essential to ensuring long-term durability and performance of a roofing system. Without it, moisture can enter the roof or wall assembly at these vulnerable points, leading to rot, mold growth, and other costly damage. For this reason, it is absolutely necessary to include flashing when installing a new roof.

How Does Roof Flashing Work?

Roof flashing works by forming an impenetrable barrier at the joints in your roof and directing water away from these areas. To do this, it is typically installed over the underlayment and below the exterior roof material (shingles, tiles, etc.), creating an additional layer of protection over your roof’s weak areas. The flashing is sealed with caulking or to make it watertight.

Where Does Flashing Go?

The specific placement of roof flashing can vary depending on the design and layout of your roof. Common places where you will find roof flashing include:

  • At the junction where the roof meets a wall or other sloped surface
  • In valleys, where two sections of a roof meet at an angle
  • Around protruding elements like chimneys, vents, and skylights
  • Along the edges of a roof where it meets the gutter system

Does Flashing Go Over or Under Shingles?

In most cases, roof flashing is installed under the shingles and over the underlayment to protect your roof system from damage and provide a seamless barrier against moisture infiltration.

Sometimes you’ll be able to see flashing over your shingles, though. For example, counter flashing is often exposed around chimneys.

What is Roof Flashing Made Of?

Flashing can be made from various metals, but the most common materials are pre-finished aluminum, steel, or copper. These durable metals are designed to withstand the elements and stand up to repeated use over many years.

Pre-finished Aluminum

Pre-finished aluminum roof flashing is a popular choice for modern roofing systems thanks to its affordability and ease of installation.


Steel is the most common material used for roof flashing. Though it’s slightly more expensive than aluminum, it is also more durable and resistant to rusting.


Copper roof flashing is one of the most durable and long-lasting options, but it can be costly compared to other materials.

Will I Ever Need to Replace My Roof Flashing?

While roof flashing is constructed to last many years, it may eventually need replacement if damaged or worn out. To keep your flashing in tip-top shape and avoid water damage to your home, a reputable roofing contractor should inspect your flashing annually to catch any issues.

Signs of Issues with Flashing on a Roof:

  • >Leaks or water damage on the roof surface
  • Cracked, warped, or missing flashing at the seams and joints
  • Aging or rusting of metal flashing components
  • Discoloration or mold growth that may indicate moisture infiltration in the roof assembly

Warren Thompson & Son Roofing & Siding Can Inspect & Fix Your Roof Flashing

If you are experiencing any of these issues with your roof flashing or want to ensure that your roof is in satisfactory condition, contact Warren Thompson & Son Roofing & Siding today. We can assess the state of your flashing and offer any necessary repairs or replacements, protecting your roof from moisture damage and prolonging its lifespan.

We’ve been in business for nearly 50 years, providing top- quality roofing services to homeowners and businesses across New Jersey and Pennsylvania. Our team of experts has the knowledge and experience needed to quickly and effectively address any issues with your roof flashing and ensure that it continues performing at its best for many years. Contact us today for an estimate!

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