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  • Tom Stratton

Understanding Flashing in the Context of Roofs

Understanding Flashing in the Context of Roofs


An essential and integral component of a solid and durable roof is flashing. Roof flashing prevents water from rain and storm from splashing against your walls and leaking into your homes. Knowing and understanding flashing and how it works is also important, besides roof materials and waterproofing. Let us delve into this critical component of roofing.

What is roof flashing?

Roof flashing is a piece of metal placed around the edges of the roofs and at the points where any projection, like chimneys, vents, or skylights, intersects with the roof. 

Flashing will prevent water from entering the house through the cracks or openings on the roof by directing the water away from the seams and joints to the gutters.

It is imperative to ensure that the flashing is installed correctly. Improper installation of roof flashing can damage the roof and your building substantially. 

Areas that need flashing: 

The areas in your roof that are particularly vulnerable to leaks and will require flashing are: 


Usually, skylights come with a border so that it becomes easy to install flashing. Sometimes skylights also come with a built-in flashing. Seek the advice of your local contractor to find the best fit. 


Vents are of two types: hood vents and pipe vents. Both vents will need flashing to prevent water from seeping into the roofs.


The base of the chimneys needs to be surrounded by flashing at the intersection where the chimney and roof meet. 


Particularly for sloped roofs with valleys, flashing will have to be installed where the two valleys meet. The angle at which the valleys meet is most vulnerable to water seepage.

Types of Flashing

As you can see, a roof has various features, and each part of the roof requires a different type of flashing. Let us understand the different types of flashing:

Base Flashing: 

Base flashing is a single metal layer installed underneath the roof shingles. It is fixed at the joint between the roofing surface and the vertical wall or parapet. This ensures that the flashing surface directs the rainwater downwards and away from the roof deck, thus protecting the roof from water damage. 

Step Flashing: 

In step flashing, L-shaped metals are placed between shingles along the sides of the wall. They are placed in a cascading design resembling steps. Like base flashing, step flashing is installed under the shingles so it is not visible from the ground.

Counter flashing: 

Counter flashing is typically installed at the base of a chimney. It is placed either above or opposite to base flashing, but unlike base flashing, counter flashing is installed on top of the shingles. 

Valley Flashing:

As mentioned earlier, a roof valley is the joint where two downward slopes of the roof meet. There is often a cleft at the point where these slopes meet, and very often, water can seep into your home through these crevices. But valley flashing, if installed correctly, will direct the water away from the roof towards the gutters. 

Drip Edge Flashing:

Drip edge flashing is installed at the edges of the roof. This type of flashing is installed to prevent rainwater from falling off the roof onto the sidewalls or seeping into the roof deck. Drip edge flashing will redirect the water to the gutters, thus protecting the roof and walls from water damage.

Vent Stack Flashing: 

Vent stacks are circular, requiring special flashing to ensure the edges are completely sealed and water doesn’t seep into the roof layers. A metal piece and a rubber gasket are used to ensure that the bottom of the vent is secured tight. 

Headwall Flashing:

Headwall flashing is an L-shaped metal flashing installed at the edge where the upper end of the roof meets the vertical wall. Installing this flashing will ensure water doesn’t seep into the gap between the roof and the wall. There are different types of headwall flashing, and selecting the right kind of flashing will depend on the roof’s pitch.

Now that we have a basic understanding of the different types of flashing that can be installed on a roof let’s look at the materials used for flashing.

Materials used in flashing: 

Flashing is mainly made out of metal, and the four common metals used are: 


  1. Aluminum is durable and can withstand extreme temperatures

  2. It is lightweight and cheaper than the other metals.

  3. Its affordability makes it a popular choice compared to other metals. 

  4. However, aluminum can rust over time

  5. It can also break faster on impact as compared to other metals

Galvanized Steel: 

  1. Galvanized steel is another popular choice of metal for flashing. 

  2. It is heavier than aluminum and can withstand damage from serious impact

  3. It is affordable

  4. Over time the galvanized coating can corrode and wear away

  5. It is heavier and hence more difficult to contour and install; thus, it is more labor and time intensive.


  1. It is highly durable and, with proper maintenance, can last up to 100 years.

  2. It is corrosion-resistant and looks very attractive. 

  3. It is lightweight and very malleable, making it easy to fit the various contours of the roof.

  4. It is one of the most expensive metals available in the market.

Tips for maintaining the flashing

Like the other elements on your roof, flashing must also be inspected regularly for damages and corrosion. The following tips will help you identify any issues with the flashing and enable you to take timely action, thus avoiding costly repairs.

Inspect regularly: 

Inspecting your flashing at least once a year, particularly after a heavy storm or rainfall, is recommended. If you spot the following red flags, then its time to contact your local roofing company: 

  1. Rust on the metal

  2. Breakage or cracks

  3. Bent metal

  4. Holes on the metal

  5. Shingles around the flashing are curled

Clean the flashing: 

Cleaning the flashing at least once a year is a good idea. It will help remove the debris and dust and help spot any signs of corrosion or rust.

Replace flashing if re-roofing

If you are planning to change your roof, it is advisable to replace the flashing too. The previous flashing would have been installed per the old roof’s specifications. 

Call a professional to install flashing: 

Above all, ensuring that your flashing is installed correctly is vital. Hire a trusted roofing company to guide you through the process and choose the right flashing for your roof. 

In conclusion

As a homeowner, knowing the features of the roof and understanding the basics of flashing and the various elements is essential so that you can make an informed decision regarding roof maintenance and repair. 

If you want a roof inspection or to schedule a free consultation, contact

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