How to Flash a Chimney: The Do's and Don'ts

How to Flash a Chimney: The Do's and Don'ts

Posted on Sept 22nd, 2023.

Chimney flashing — a seemingly small yet crucial component of your roof — plays a significant role in safeguarding your home from water damage and maintaining its structural integrity. 

In this article, we'll delve into the essential do's and don'ts of chimney flashing, helping you understand how to flash a chimney properly. 

Whether you're a homeowner or a professional in the roofing industry, this knowledge will empower you to protect your property from costly leaks and ensure your chimney flashing is up to the task.

What is Chimney Flashing?

Chimney flashing may not be the first thing that comes to mind when you think of roofing, but it's a critical component that ensures your home remains dry and structurally sound. Essentially, chimney flashing is a barrier designed to prevent water from seeping into the gap where your chimney intersects with the roof.

Flashing typically consists of thin metal strips, often made of materials like copper or galvanized steel. These strips are strategically placed around the base of the chimney and integrated into the roof's structure. When properly installed, chimney flashing acts as a safeguard against water infiltration.

Why Chimney Flashing Matters

Chimney flashing is essential for:

  • Waterproofing: Chimney flashing creates a waterproof barrier, preventing water from seeping into your home. Without proper flashing, rainwater can infiltrate the chimney's base and roof, leading to leaks and extensive water damage.
  • Structural Integrity: By directing water away from vulnerable areas, chimney flashing helps maintain the structural integrity of your roof and chimney. Water damage can weaken the roof's support structure and compromise its stability.
  • Preventing Leaks: Leaks can cause a host of problems, from damaged ceilings and walls to mold growth. Chimney flashing is crucial in preventing these issues by keeping water out of your home.
  • Longevity: Properly installed and maintained chimney flashing can extend the lifespan of your roof and chimney. It shields these critical components from moisture-related deterioration.

Let's dive now into the process of chimney flashing.

How to Flash a Chimney

Chimney flashing is a precise process that, when done correctly, can effectively protect your home from water infiltration. In this section, we'll outline the step-by-step process of how to flash a chimney.

1. Assessment and Preparation

Begin by assessing the condition of your existing flashing, if applicable. Remove any old or damaged flashing material. Ensure that the chimney and roof surfaces are clean and free of debris.

2. Select the Flashing Material

Choose the appropriate flashing material for your project. Copper and galvanized steel are popular choices due to their durability and longevity.

3. Measure and Cut Flashing Strips

Measure and cut the flashing material into strips. These strips will be used to create the layers that form the waterproof barrier.

4. Install Step Flashing

Start with step flashing, which is individual pieces of flashing that are layered step-by-step along the chimney's base. Each piece should be carefully aligned and securely attached to the chimney and roof.

5. Counterflashing Installation

Install the counterflashing, which is another layer of flashing that covers the step flashing. This layer is typically embedded into the chimney mortar joints to create a seamless, watertight seal.

6. Seal the Joints

Use professional-grade roofing sealant to seal all joints and seams in the flashing. Pay close attention to detail, ensuring there are no gaps where water could penetrate.

7. Angle the Flashing

Ensure that the flashing has a slight angle away from the chimney. This angle directs water away from the vulnerable areas and prevents pooling around the chimney base.

8. Inspect for Quality

After installation, thoroughly inspect the chimney flashing to ensure it's secure, watertight, and free of defects.

Properly flashing a chimney is a task that requires precision and attention to detail. When done correctly, it forms a robust barrier against water infiltration, protecting your home from leaks and structural damage.

Now that we've covered the basics of chimney flashing and what it entails, let's delve into the essential do's and don'ts to ensure your flashing serves its purpose effectively.

The Do's of Chimney Flashing

When it comes to chimney flashing, certain practices are essential to ensure your roof remains watertight and free from leaks. In this section, we'll highlight the key actions and approaches you should follow for successful chimney flashing.

1. Use Quality Materials

Invest in high-quality flashing materials such as copper or galvanized steel. These materials are durable and provide long-lasting protection.

2. Seal All Joints Properly

Ensure that all joints and seams in the flashing are sealed tightly. Use professional-grade roofing sealant to create a watertight barrier.

3. Employ Step Flashing

Implement step flashing, a technique where individual pieces of flashing are layered step-by-step along the chimney. This method offers excellent water diversion and protection.

4. Overlap Flashing Correctly

Overlap flashing sections correctly to prevent water from penetrating between them. Proper overlap ensures continuous protection.

5. Maintain Proper Angle

Flashings should have a slight angle away from the chimney, directing water away from vulnerable areas. This helps prevent water from pooling around the chimney base.

6. Perform Regular Inspections

Regularly inspect your chimney flashing to catch potential issues early. This proactive approach can save you from costly repairs down the road.

The Don'ts of Chimney Flashing

Chimney flashing is a critical aspect of roof maintenance, but it's equally important to know what not to do. In this section, we'll explore the common mistakes and practices to avoid when dealing with chimney flashing, ensuring that your flashing job remains effective and durable.

1. Avoid Cheap Flashing Materials

Don't cut corners with subpar flashing materials. Inferior materials can deteriorate quickly, leading to leaks and costly repairs.

2. Don't Skip Sealing

Never neglect sealing. Inadequate sealing can result in water infiltration and undermine the integrity of your chimney flashing.

3. Say No to Improper Installation

Never allow for improper installation. Flashing should be installed by experienced professionals to ensure it's done correctly.

4. Don't Overlap Incorrectly

Avoid overlapping flashing sections incorrectly. Poor overlap can create gaps that allow water to infiltrate, leading to leaks.

5. Avoid Incorrect Angles

Don't forget to maintain the proper angle. Flashings should be angled away from the chimney to prevent water accumulation.

6. Avoid a DIY Approach

While some minor flashing repairs can be tackled as DIY projects, it's advisable to seek professional help for significant issues. Professional roofers have the expertise to diagnose and address complex flashing problems effectively.


Proper chimney flashing is vital for preserving your roof's integrity and protecting your home from water damage. Following the do's and don'ts outlined in this guide will help you maintain a watertight seal and extend the lifespan of your roof.

For expert chimney flashing services, including copper chimney flashing, contact Perun Roofing.

Call us at (773) 574-1317 or via email at [email protected]. Don't wait until water damage occurs — ensure your chimney flashing is in top condition today.

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