What Is Roof Flashing & How It's Installed

May 6, 2024

Roof flashing is a thin metal layer under your roof shingles. Although it may not be the most noticeable part of your roof, it is indispensable in protecting your home from water damage. 

Whether you're looking to educate yourself about the components of your roof, preparing for a roof replacement, or simply curious about how professional roofers do their job, this guide from Cloud Roofing has everything you need to get started. 

What Is Roof Flashing?

Roof flashing prevents water from penetrating your home where the roof joins other parts of the house, such as chimneys, vent pipes, skylights, or intersections at roof valleys. It acts as a seal that bridges gaps between roofing materials and other parts of the house.

Why Is Roof Flashing Important?

Roof flashing is essential for protecting a building from water damage at points where the roof meets other structures or features. Water can seep into roof joints without proper flashing and cause mold, rot, and structural damage. Effective flashing serves as the first line of defense against water penetration, extending the life of your roof and reducing the need for costly repairs. 

Different Types of Roof Flashing

Here are the main types of roof flashing used in construction:

  1. Chimney Flashing: This prevents water from entering where the chimney penetrates the roof. It typically involves several parts, including step flashing that integrates with the shingles, counter flashing that attaches to the chimney, and a cricket or saddle that diverts water around the chimney base.
  2. Valley Flashing: Installed in the valleys where two roof slopes meet, valley flashing channels water down the roof and away from the structure. It's often made of a wide sheet of metal that sits beneath the shingles.
  3. Drip Edges: These are installed along the roof's edge to direct water away from the fascia and into the gutters. Drip edges prevent water from seeping under the roofing material at the edges. Professional roofers install drip edge flashing around gables, eaves, and rakes.
  4. Step Flashing: Used where a vertical surface like a wall or dormer intersects a sloped roof. It consists of short, rectangular pieces of flashing material that are layered with each course of shingles to ensure water sheds over the shingle below.
  5. Vent Pipe Flashing: Also known as pipe boots, these are installed around plumbing vents. They usually consist of a rubber or flexible collar that tightly fits the pipe, preventing water ingress around the vent.
  6. Skylight Flashing: Custom flashing kits are often used around skylights to ensure a watertight seal. These can include continuous flashing at the base, step flashing along the sides, and solid pieces at the top.
  7. Kickout Flashing: Installed at the point where the roof edge meets a sidewall, kickout flashing diverts water into the gutter, preventing it from running down the side of the building where it can cause water damage.
  8. Apron Flashing: Creates a water-resistant barrier where a roof slope meets a vertical surface, like a wall or dormer. It is also commonly used around chimneys. Apron flashing prevents structural damage, mold, and other moisture-related issues.

Each type of flashing has a specific role in preventing water from penetrating the roof and causing damage to the structure, highlighting the importance of proper installation and regular maintenance. Roofers will also use the proper roof flashing sealant types according to the flashing material and location.

Roof Flashing Materials

Different materials are used for flashing based on their durability, cost, and the specific roofing material they complement. It's typically made from aluminum, copper, galvanized steel, or rubber and is designed to be durable and flexible. But those aren't the only options. 

Here are the most common roof flashing materials:

  1. Aluminum: Lightweight and corrosion-resistant, aluminum flashing is popular because it's easy to form and install. It's especially common in residential roofing.
  2. Galvanized Steel: This is steel coated with a layer of zinc to prevent rust. Galvanized steel flashing is very durable and more corrosion-resistant than plain steel. Due to its strength and cost-effectiveness, it's one of the most common materials used for flashing.
  3. Copper: Known for its long lifespan and durability, copper roof flashing is highly resistant to corrosion and can be soldered, creating watertight seals. Some homeowners prefer to install roof flashing made of copper because, over time, it develops an aesthetically pleasing green patina. It is more expensive than other materials but is popular for high-end or historic applications.
  4. Lead: Lead is extremely durable and flexible, making it easy to mold into complex shapes. It's perfect for flashing around chimneys and in other intricate areas. However, due to lead-related health concerns, its use has declined in residential applications.
  5. Zinc: Similar to copper, zinc is durable, corrosion-resistant, and develops a protective patina. It's more affordable than copper and is eco-friendly due to its lower melting point, requiring less energy.
  6. PVC and Other Plastics: Plastic flashing, often made from PVC, is used where flexibility and corrosion resistance are needed. It's commonly used around vent pipes and other protrusions. While not as durable under high heat or UV exposure as metal flashings, it's cost-effective and easy to install.
  7. Rubber: Often used in vent pipe flashing, rubber is valued for its flexibility and ability to create a tight seal around irregular surfaces. Rubber flashing is often reinforced with a metal base to improve durability.

Each material has advantages and is chosen based on specific roofing needs and budget considerations. Proper selection and installation are key to ensuring that flashing performs its role effectively.

What Is the Plumbing Vent Flashing Boot?

Plumbing vent flashing is a fitting that wraps around the plumbing vent pipe protruding from the roof. It typically consists of a flat base that integrates with the roof material and an upwardly extending sleeve that fits snugly around the pipe. The flashing design ensures that any water running down the roof or along the pipe is directed away from the opening and cannot penetrate the interior of the building.


A plumbing vent flashing boot typically consists of two main components:

  1. Base: This is the flat part that sits flush against the roof. It's usually made of a durable material like metal (aluminum, galvanized steel, or copper) or sometimes plastic or rubber. The base is designed to overlap with roofing materials such as shingles, integrating seamlessly to prevent water leakage.
  2. Collar: This part is cylindrical and fits tightly around the plumbing vent pipe. It's often made from flexible materials like rubber or silicone, which can adapt to the size and shape of the pipe, creating a snug seal. The collar's flexibility is crucial as it must accommodate slight movements and vibrations of the pipe without cracking or tearing.

How to Install Flashing

Installing roof flashing correctly is critical for maintaining the integrity of your roof, especially at points where the roof surface is the most vulnerable to water damage. Here's a basic guide on installing different roof flashing types.

Step 1: Prepare the Area to Install Flashing

  • Clean the Area: Remove any old flashing, debris, and loose roofing materials from the area where the new flashing will be installed.
  • Inspect for Damage: Check for any signs of rot or damage in the roofing materials and structure. Repair these issues before proceeding.

Step 2: Measure and Cut the Flashing

  • Measure: Carefully measure the area where the flashing is to be installed—each piece of flashing needs to be tailored to fit the specific area snugly.
  • Cut the Flashing: Using the measurements, cut the flashing material to size with the utility knife or tin snips.

Step 3: Fit Flashing

  • Dry Fit: Place the flashing piece in the intended location to ensure it fits properly. Adjust if necessary before securing it.
  • Shape Flashing: For certain types of flashing, like step flashing, you may need to bend the material to fit the contours of the roof and walls.

Step 4: Secure Flashing

  • Attach Flashing: Use roofing nails or screws to secure the flashing into place. Make sure the nails are spaced appropriately (typically about every 12 to 18 inches).
  • Overlap Pieces: When using multiple pieces of flashing (like in step flashing), have each piece overlap the one below it by at least 2 inches to promote proper water flow.

Step 5: Seal and Waterproof

  • Apply Sealant: Use roofing cement or an appropriate sealant to cover the nail heads and any gaps where water might penetrate.
  • Ensure Proper Overlap: For installations involving shingles, lay the shingles over the base of the flashing. The top of the flashing should be under the shingles to allow water to flow over the flashing without entering the roof.

Specific Considerations for Different Types of Flashing

  • Chimney Flashing: Includes installing base flashing around the bottom of the chimney and counter flashing that is embedded into the chimney masonry to cover the base flashing.
  • Valley Flashing: This is typically a W-shaped or V-shaped piece installed before the shingles and runs along the valley of the roof.
  • Step Flashing: Used where a roof meets a wall. Install a piece of flashing for each course of shingles, ensuring each step is covered by the next row of shingles.

Final Checks

After installation, carefully inspect the entire area so all parts are secure and properly sealed. If possible, test the flashing with water to ensure there are no leaks. However, due to the delicate nature of the flashing, it’s highly recommended you leave the job to skilled professionals, like the Cloud Roofing team. That way, the installation process is completed correctly and without hassle. 

When Is it Time to Repair a Roof Flashing?

Roof flashing is essential for keeping your home dry and protected from water damage, but over time, it can deteriorate and may need to be repaired. Whether you need to replace your roof flashing when replacing your roof depends on several factors, including the condition of the existing flashing, the type of new roofing materials being installed, and the specifics of the roof design.

Here are key indicators and situations when it's time to repair roof flashing, whether you need your roof replaced as well or not.

1. Visible Damage

Inspect the flashing for any visible signs of cracks, holes, or breaks. Metal flashing can corrode or rust, while plastic or rubber boots around vents may crack due to exposure to the elements. Flashing that appears bent, warped, or otherwise deformed can indicate that it no longer provides a tight seal against water.

2. Leaks and Water Damage

The flashing in these areas may fail if you notice water stains directly below roof structures, such as chimneys, vents, or along walls adjoining the roof. Remember to check your attic after rain for any signs of dampness or mold, which could suggest water is getting past the flashing.

If you find a roof flashing leak, you will need to have the faulty flashing repaired as soon as possible, along with the damage to your roof, ceiling, or drywall, depending on the leak's location.

3. Loose or Displaced Flashing

Flashing should be securely attached. If it has become loose, it may not effectively keep out water. Severe weather conditions like high winds or hail can displace flashing, compromising its effectiveness.

4. During Roof Repairs

If you're replacing or repairing a significant portion of your roof, it's a good time to inspect and possibly replace the flashing. This ensures that the new roofing materials are well integrated with the waterproofing system. Inspect your flashing for damage after any major storm or severe weather event as part of a general roof check.

5. Aging and Corrosion

The lifespan of flashing depends on the material. For example, aluminum and galvanized steel may last around 20 years, while copper can last much longer. If your roof's flashing is old or nearing the end of its expected lifespan, inspect it more frequently and prepare for possible repairs or replacement. Metal flashing can rust over time, especially in environments with high salt exposure or acidic rain. Corrosion weakens the flashing and creates gaps for water entry.

6. Poor Installation

Sometimes, initial symptoms of leaks or damage are due to poor installation. If flashing seems like it's improperly installed (e.g., inadequate sealing, incorrect placement), it may need to be reinstalled correctly.

Maintenance Tips for Roof Flashing

Regular inspections are key to identifying potential issues early.

  • Regular Inspections: Check flashing at least twice a year for signs of wear and tear. Look for rust, cracks, or separation from the roofing material.
  • Prompt Repairs: If you notice any damage, address it immediately. Small issues can lead to bigger, more expensive problems if water starts to infiltrate your home.
  • Professional Installation: Always have flashing installed by a qualified professional. Incorrect installation can lead to failure and water damage.
  • Keep It Clean: Remove debris and dirt buildup from around flashing areas to prevent blockages and water pooling.

If you're not comfortable doing these inspections yourself or if you identify potential problems, it's wise to contact a professional roofer. They can provide a thorough assessment and carry out any necessary repairs to ensure your roof remains in good condition and continues to protect your home effectively.

Schedule a Flashing Inspection with Cloud Roofing 

Roof flashing may not be the most visible part of your roof, but it is undoubtedly one of the most critical. By understanding what it is, recognizing its types, and maintaining it properly, you can rest easy knowing your roof is protecting your home.

For expert advice or to schedule a roofing inspection, contact Cloud Roofing. We provide FREE quotes to help keep your roof in top condition!

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