Everything You Need to Know About Roof Flashing
By Cynthia Pigeon
Updated on November 3, 2025
It is no secret that a leaky roof can have severe budgetary repercussions: moisture problems, heat loss, and property damage.
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To avoid such problems, avoid neglecting the installation of flashing on your roof.
Roof Flashing: Definition & Purpose
Source: Canva
Roof flashing—whether plastic, aluminum or steel—is a form of moulding that can be found in many different roof areas: in valleys, around plumbing vents, at the base of chimneys or roof vents.
Its purpose is to ensure that the roof is watertight in regard to the above-mentioned sections. Specifically, it allows the water to drain to the gutters and not stagnate on the surface of the roof, thus avoiding any water infiltration.
Furthermore, the seal provided by the flashing also prevents heat loss and therefore, any further expenses added to your heating bill.
While mortar flashings can be made by a seasoned professional, the materials above-mentioned are more durable and the fact that they are premade significantly speeds up their installation.
Installing Roof Flashing
Looking to install your own roof flashings? While it is possible to do so, note that it is a task that presents its share of challenges, including working at heights and having good manual skills in order to adequately perform the installation. So, feel free to call in a professional contractor!
Maintenance Needed
Source: Canva
Surely you want your flashings to last through the years while still looking good? Make minor repairs as soon as they are needed.
Have you noticed any small holes in your flashing? Do not wait to seal it with a gutter putty, do it right away! Make sure to clean the surface beforehand with a small wire brush.
Need more information regarding new roofing materials? Check out our article Which Roofing Material Will Best Suit Your Needs?
Counter-Flashing
To ensure roof flashing has maximum adhesion to the roofing material, it is equipped with a counter-flashing. There are two types of flashing: external and internal flashing.
External flashing: External flashing or exposed flashing is used to prevent moisture from seeping into the existing structural walls where the roof intersects the wall.
Internal flashing: Internal flashing or concealed flashing collects water that has penetrated any given wall of the building and then drains it out of the wall through drain holes.
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