What Is Chimney Flashing and Why Is It Important?

Chimney with flashing

Vital for protecting against moisture damage, chimney flashing is the metal sheet placed at the edge of chimneys to create a watertight seal. When it fails, it can lead to leaks and other issues.

If you’re unfamiliar with this type of flashing, don’t worry. We’ll discuss everything about chimney flashing, why it’s important, and what types are available. We’ll also share how you can tell when it’s time for a replacement, as well as the materials required and steps involved in replacing your flashing.

Chimney Flashing: What It Is

Chimney flashing is a metal sheet installed at the contact point between your chimney and roof. It creates a watertight seal that protects against water penetration and damage. When properly installed, chimney flashing can last over 30 years, though factors such as where you live, the materials used, and the size and shape of your chimney also can influence its lifespan.

Common Materials Used for Chimney Flashing

If you’re in the market for new chimney flashing, these are the flashing materials to choose from:

  • Aluminum: It’s a popular choice among homeowners due to its low cost and ease of installation on any type of roof. Aluminum is also quite resistant to rust, which makes a difference long-term.
  • Steel: This material is likewise commonly used to manufacture chimney flashing. It’s not only durable, but it has excellent anti-rust properties.
  • Copper: While expensive, copper is the obvious choice if you want durability, curb appeal, and a lightweight material. Copper also never rusts and can withstand any weather conditions.
  • Vinyl or PVC: This flashing material has grown in popularity because it offers similar benefits to metal flashing minus a complicated installation process. The downside? It lacks durability and resistance to extreme weather conditions.

Why Is Chimney Flashing Important?

roof chimney flashings
Photo Credit: Danler / Canva Pro / License

Chimney flashing is an essential part of a chimney system. It wraps around the chimney and extends to the roof, adjusting differences in inclination and pitching to stop water from leaking into your home. Properly installed chimney flashing provides these remarkable benefits:

  • Thermal efficiency: Chimney flashing provides thermal protection, preventing heat from escaping your home and lowering your utility bills. 
  • Moisture damage protection: Internal damage is easily avoided by installing chimney flashing. It can help keep debris, dust, water, and other particles from entering the roof cavity. Instead, it directs them down the roof, into the gutter system, and away from your home.
  • Pest control: Pests are continually looking for ways to enter roofing systems. Keep rats, possums, and other unwelcome pests away from your home by installing high-quality flashing along the entire perimeter of the chimney structure, where it meets the roof. 
  • Structural stability: Without chimney flashing, water can flow right into your home, rotting wood and enabling mold growth. Schedule regular chimney inspections to determine the condition of your chimney system, including flashing.

Types of Chimney Flashing

If it’s your first time installing chimney flashing, you may be surprised to know that there’s quite a selection. Keep reading to discover each flashing type and how it can benefit your home.

Step Flashing

As the most common type of flashing used in homes, step flashing is suitable for most chimney shapes and sizes. It’s an L-shaped piece of metal placed interwoven with the roof’s shingles and extending along the walls of the chimney. Step flashing is pretty simple to install and budget-friendly to boot.

Apron (Continuous) Flashing

Apron flashing is installed along the base of the chimney. But unlike step flashing, a long piece of sheet metal is bent to perfectly fit the chimney and roof. While this type of flashing costs more than step flashing, it’s ideal for larger chimneys and areas with a lot of rainfall.

Counter Flashing

Roofers use counter flashing to protect the base of the chimney at the meeting point with the roof. It goes over the step or continuous flashing and extends down the walls of the chimney. Counter flashing is applied in two layers: a first layer as the base and a second layer that is inserted into the chimney brickwork. 

Cap Flashing

Cap flashing is generally made of metal and placed around the chimney flue to block water from entering the chimney. It’s especially useful in mitigating water damage in areas with heavy snow or rainfall.

Cricket Flashing

If you have a bulky chimney regularly exposed to pooling water on the roof, cricket flashing is a good option to consider. A cricket is a triangle-shaped structure built behind the chimney to direct water away from the chimney. Once the shape is created, metal flashing is added on top to seal the structure.

Signs You Need To Replace Chimney Flashing

Bad chimney flashing
Photo Credit: Sandul1234 / Wikimedia Commons / CC BY-SA 4.0

As the elements can do a number on your chimney flashing, it’s a good idea to perform chimney inspections occasionally. Most homeowners perform this task when it’s time to replace or repair the shingles on their roofs. If you notice rusting or other damage, replace your flashing to avoid opening up your home to water damage.

During your inspection, check for these worrisome signs you need to replace your chimney flashing:

  • Cracks in the mortar joints or the brick
  • Leaky chimney
  • Eroded or crumbling crown
  • Flaking chimney tiles
  • Deteriorated chimney brickwork
  • Signs of corrosion, such as rust forming at the edges of the flashing

How To Replace Chimney Flashing

If climbing a ladder and handling various working tools isn’t a problem, chimney flashing repair or replacement should be fairly straightforward.

To begin, you’ll need the following tools:

  • Putty knife
  • Masonry screws or nails
  • Hammer
  • Cement
  • Chisel
  • Working gloves
  • Replacement flashing material

Steps for replacing chimney flashing:

  1. Start by removing debris like leaves or twigs that may have gotten stuck between the chimney and the flashing. 
  2. Using your chisel and hammer, remove as much old roofing cement as you can and attach the new flashing to the brick using nails or screws. 
  3. Generously apply new roofing cement between the chimney and the flashing and apply pressure. Once everything is set, apply more cement to the top edge of the flashing and smooth it out with a putty knife.

While following these steps is doable, it can likewise be a challenge many homeowners aren’t willing to undertake. The job often occurs around 30 to 40 feet above the ground and requires skill, precision, and experience. Before you take on the task yourself, consider the following:

  • To access the roof, you’ll need a safe extension ladder and someone to hold it on the ground. Be careful on the roof, as falling is common, especially on steep roofs.
  • When removing the old flashing, be careful not to cut or injure yourself, and don’t start the job without safety gear.
  • Measuring, cutting, and bending the chosen flashing material should be done before the installation.
  • Work should start in the early morning before the sun has had a chance to bake your roof.
  • The adhesive and shingles tend to become more flexible in hot weather, making them more challenging to handle and remove.

Cost of Replacing Chimney Flashing

To avoid roof and home damage, take action as soon as you detect any flashing problems. You can fix a chimney leak by resealing the flashing using roofing cement, caulk, or other types of sealant. But this is only possible if the flashing has been installed correctly and there is no warping or flaring at the edges. 

Depending on your chimney size and type, roof type, and flashing material, the cost of resealing flashing can range from $150 to $400. In case of replacement, you can expect to pay anywhere from $350 to $1,550.

FAQ About Chimney Flashing

What Factors Determine the Lifespan of Chimney Flashing?

Correctly installed and maintained chimney and roof flashing can last around 30 years. Factors such as the size and shape of the chimney, the materials used, the workmanship, and the climate in your area all determine the lifespan of your flashing.

Can My Chimney Flashing Be Repaired Without Removing the Shingles?

To correctly install new flashing, you’ll need to remove the shingles around your old flashing and rearrange them once the installation is complete. You’ll prevent roof leaks and other roof damage that can lead to costly repairs.

What Are the Best Types of Sealants Used on Flashing?

Use sealants such as polyurethane or butyl to make flashing water-resistant and as durable as possible. Thermoplastic polyolefin (TPO) is often used in commercial roofing to prevent cracking and subsequent breaking, though homeowners are also increasingly turning to this sealant type.

Get Help From a Chimney Professional

Repairing or replacing your chimney flashing requires a certain level of skill, expertise, effort, and care. You’ll need the proper tools to complete the project, which may take longer than you initially expected, leaving your chimney and roof exposed to the elements while you work on the repair or replacement.

While you can do it all on your own, it’s not an easy task. For a proper and safe installation, the best choice is to call a local chimney professional. They can inspect your roof and chimney, provide an accurate estimate, and inform you of other issues.

Main Photo Credit: NagyDodo / Canva Pro / License

Andie Ioo

In my free time, I enjoy traveling with my husband, sports, trying out new recipes, reading, and watching reruns of '90s TV shows. As a way to relax and decompress, I enjoy landscaping around my little yard and DIY home projects.