Chimney Flashing

Definition: Chimney flashing is a waterproofing component used to seal the gap between a chimney and the metal roof, preventing water from entering the roof structure where the two surfaces meet.

This part is essential in areas like chimneys because they interrupt the natural flow of water off the roof, making them prone to leaks and water damage. Chimney flashing is usually made from materials like aluminum, copper, or galvanized steel, chosen for their durability and resistance to weathering.

Types of Chimney Flashing

Step Flashing: This type of flashing is installed in layers along the chimney’s sides, “stepped” up to match the slope of the roof. Each section of step flashing overlaps the one below it, allowing water to flow down without penetrating the roof.
Counter Flashing (Cap Flashing): Counter flashing is installed over the step flashing, embedded into the mortar joints of the chimney. This helps secure the flashing to the chimney and provides additional protection by directing water away from the gap.
Base Flashing: This is the piece of flashing installed at the base of the chimney, typically on the lower side, where it meets the roof. Base flashing is installed to ensure a watertight seal along the roofline.
Cricket Flashing: A cricket or saddle flashing is a peaked structure installed behind the chimney to divert water around it, especially on larger or wider chimneys. This prevents water from pooling and reduces the risk of leaks.

Learn more: What is Cap Flashing?

Materials Used

Aluminum: Lightweight and affordable, aluminum is the most commonly used material for chimney flashing. It is easy to install and can be painted to match the roof or chimney.
Copper: Copper flashing is durable and visually appealing, often used in higher-end or historic buildings. It develops a natural patina over time, adding character and corrosion resistance.
Galvanized Steel: Galvanized steel is strong and affordable but may require periodic maintenance, as it can rust over time, especially if the protective coating wears off.

Installation Process:

Prepare the Roof Surface: The roof area around the chimney is cleaned and prepared to ensure a secure fit for the flashing.
Install Base Flashing and Step Flashing: Base flashing is installed at the base of the chimney, followed by layers of step flashing on each side, overlapping to create a watertight seal.
Apply Counter Flashing: Counter flashing is installed over the step flashing and embedded into the chimney’s mortar joints for added security.
Add Cricket Flashing (if needed): For larger chimneys, a cricket is installed behind the chimney to divert water.

Importance of Chimney Flashing:

Prevents Leaks: Chimney flashing helps keep water from entering the roof structure, protecting the chimney and surrounding roof deck from water damage and rot.
Extends Roof Life: By providing a watertight seal around the chimney, flashing helps protect the structural integrity of both the chimney and the roof, extending their longevity.
Reduces Maintenance Costs: Properly installed flashing reduces the need for frequent repairs due to water damage, saving on long-term maintenance costs.