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When it comes to protecting your roof and preventing water infiltration, proper installation of metal roof flashing is crucial. Metal roof flashing is a thin, flexible material that helps direct water away from critical areas of your roof, such as where the roof meets a wall or chimney. In this comprehensive guide, we will walk you through the step-by-step process of installing metal roof flashing to ensure a watertight seal and long-lasting protection for your roof.

Understanding Metal Roof Flashing

Metal roof flashing serves as a barrier between your roof and potential water entry points. It helps to redirect water away from vulnerable areas, preventing leaks and potential damage to your roof deck and interior. There are different types of metal roof flashing, each designed for specific areas of your roof. Some common types include continuous flashing, base flashing, counter-flashing, and step flashing.

Continuous Flashing

Continuous flashing, also known as apron flashing, is a long piece of metal that carries water down to the shingles below. It is typically used where the roof plane meets a vertical surface, such as a wall or dormer. To ensure flexibility and prevent warping, long pieces of continuous flashing often have built-in expansion joints.

Base Flashing

Base flashing is used in conjunction with continuous flashing, particularly around chimney installations. It consists of two pieces of flashing, with the base flashing placed around the bottom of the chimney to direct water downwards.


Counter-flashing complements base flashing and is installed above it. It acts as a protective layer to prevent water from seeping behind the base flashing. Counter-flashing is commonly used in chimney and wall applications.

Step Flashing

Step flashing is a rectangular piece of flashing bent at a 90-degree angle in the centre. It is used for roof-to-wall flashing, ensuring that water flows away from the wall and into the gutter. Step flashing is installed in layers with shingles, allowing water to cascade down each step.

Preparing for Installation

Before you begin installing metal roof flashing, it’s essential to gather all the necessary tools and materials. Here’s a list of items you’ll need:

  • Metal roof flashing: Choose a material suitable for your specific roofing needs, such as aluminium or copper.
  • Roofing cement or silicone sealant: This will be used to create a waterproof seal between the flashing and the roof.
  • Metal cutting snips: These will help you cut and shape the flashing to fit your roof.
  • Scrub pad or cleaning solution: Use this to clean the roof surface before installation.
  • Screwdriver or drill: You’ll need this to secure the flashing in place.

Cleaning the Roof Surface

To ensure a secure and watertight installation, it’s important to clean the roof surface before installing metal roof flashing. This will remove any dirt, debris, or existing flashing that may interfere with proper adhesion. Follow these steps to clean the roof surface:

  • Begin by removing any existing flashing or debris from the area where the metal roof flashing will be installed.
  • Use a scrub pad or cleaning solution to clean the roof surface thoroughly. This will help create a clean and smooth surface for the flashing.
  • Rinse the roof surface with water to remove any residue from the cleaning process.
  • Allow the roof surface to dry completely before proceeding with the installation.

Marking the Installation Area

Once the roof surface is clean and dry, you can proceed to mark the area where the metal roof flashing will be installed. This will help guide the placement and ensure a precise installation. Follow these steps to mark the installation area:

  • Measure and mark the width of the sidewall trim if applicable. This will help determine the dimensions of the flashing.
  • Using a marker or pencil, make an outline of the flashing on the roof surface. Take into account any corners or angles that may require additional flashing pieces.
  • Double-check the dimensions and placement of the flashing outline to ensure accuracy before proceeding with the installation.

Installing Metal Roof Flashing

Now that you have prepared the roof surface and marked the installation area, it’s time to install the metal roof flashing. Follow these steps for a successful installation:

  • Apply a generous bead of roofing cement or silicone sealant along the inside of the marked outline. This will create a waterproof seal between the flashing and the roof surface.
  • Place the metal roof flashing over the cement or sealant, ensuring a tight fit over the contours of the roof.
  • Secure the flashing in place using screws or nails, following the manufacturer’s recommendations. Be sure to drive the fasteners into the roof deck, avoiding the vertical wall to allow for expansion and contraction.
  • Apply another bead of roofing cement or silicone sealant around the edge of the flashing, as well as on top of the screws or nails. Smooth out the sealant using a finger or tool to ensure a watertight seal.
  • If necessary, repeat the installation process for additional flashing pieces, ensuring proper overlap and secure fastening.

Installing Step Flashing

If your installation requires step flashing, follow these additional steps to ensure proper installation:

  • Begin by placing a piece of step flashing on top of the first row of shingles that butts up against a vertical wall or structure.
  • Embed each step flashing piece in a layer of roofing cement or silicone sealant, ensuring a secure bond with the roof surface.
  • Secure the step flashing to the roof deck using screws or nails, following the manufacturer’s recommendations. Avoid nailing the flashing pieces to the vertical wall to allow for movement.
  • As you proceed up the roof, position each step flashing piece so that the overlaying shingle will cover it completely. The end of each shingle adjacent to the wall should also be embedded in a layer of roofing cement or silicone sealant.
  • Continue installing flashing and shingles in alternating overlapping steps up the roof, ensuring proper sealing and alignment.

Maintaining Metal Roof Flashing

Proper maintenance of metal roof flashing is essential to ensure its longevity and effectiveness in protecting your roof. Regular inspections and maintenance can help identify any issues early on and prevent potential leaks. Here are some maintenance tips for metal roof flashing:

  • Inspect the flashing regularly for signs of damage, such as cracks, gaps, or loose fasteners. Repair or replace any damaged flashing promptly.
  • Clear any debris or buildup around the flashing to prevent water accumulation and potential damage.
  • Check for proper alignment and sealing of the flashing. Reapply roofing cement or silicone sealant as needed to maintain a watertight seal.
  • Trim any overhanging tree branches that may come into contact with the flashing, as they can cause damage or obstruct water flow.
  • If you notice any signs of water infiltration or leaks, consult a professional roofer to assess the situation and make necessary repairs.


Installing metal roof flashing is an essential part of any roofing project. By following the step-by-step guide outlined in this article, you can ensure a proper and watertight installation that will protect your roof from potential leaks and damage. 

Remember to prioritise safety, use the appropriate tools and materials, and perform regular maintenance to keep your metal roof flashing in optimal condition. If you’re unsure about any aspect of the installation process, don’t hesitate to consult a professional roofer for assistance. With proper installation and maintenance, your metal roof flashing will provide long-lasting protection for your roof and home.