by Kenton Shepard and Nick Gromicko, CMI®
Flashing is sheet metal fabricated to a specific shape and designed to prevent water from penetrating the roof system. It’s used in areas of a roof that are especially likely to leak.
If enough moisture gets past the flashing, it can cause both cosmetic and structural damage.
The IRC doesn’t give specific flashing details that have to be followed; it just says that flashing has to be corrosion-resistant and installed in a manner that prevents moisture entry.
Multiple methods can be used to install flashing correctly, so you won’t always be looking for one method and calling everything else a defect. You’ll be trying to confirm that flashing is installed in a manner which will prevent moisture entry, and you’ll be looking for corrosion.
In commenting on corroded flashing, you won’t be recommending repair. Flashing is simply replaced when it becomes too corroded. Your comments will either mention the presence of…
...moderately corroded flashing, which may need to be replaced soon, or…
...severely corroded flashing, which needs replacement soon to avoid damage from moisture intrusion.
Flashing that has failed due to corrosion should be replaced immediately.
For inclusion in inspection reports, you’ll find illustrations of properly installed flashing on the InterNACHI website. Studying flashing details will also help you learn to recognize what works and what doesn’t work in different situations.
During inspections, you’ll encounter situations where areas should have flashing but are hidden behind the roof-covering materials, so you won’t be able to confirm its presence. Your inspection report should contain a disclaimer which makes your client aware of this limitation and which disclaims responsibility for problems resulting from any such conditions.
Some kinds of metals corrode more easily than others, and the rate at which flashing corrodes will also depend on the quality of the flashing, and the climate in which the home is located.
Galvanized steel is the material most commonly used for flashing. Lead is sometimes used in situations where flashing needs to conform to a certain shape.
You may see steel rusted intentionally to achieve a certain look. This metal roofing was left untreated to rust naturally. The galvanized gutters were chemically treated to rust them in order to match the roof. The inside of the gutters was not rusted.
You’ll also see copper flashing, especially on high-end homes, and especially in coastal environments. You can tell something about the age of copper flashing by its color or "patina."
This chart shows how patinas change as copper ages.
This house has old copper flashing.
You may also see galvanized steel flashing painted to look like both new…
…and old copper. Sixteen-gauge copper is the gauge most commonly used for flashing. It has a lifespan of about 70 years, although this can vary, depending on the environment in which it’s installed.
On homes with tile roofs, you may see lead used as flashing, since it conforms well to the tile profile.
You may also see aluminum flashing, but it’s not common.
Learn how to master a roof inspection from beginning to end by reading the entire InterNACHI series: Mastering Roof Inspections.
Take InterNACHI’s free, online Roofing Inspection Course
Mastering Roof Inspections
Roofing Underlayment Types
Inspecting Underlayment on Roofs
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