Roof flashing prevents leaks and maintains the integrity of your roof.
Various types of roof flashing serve different roof protection purposes.
Steel is the most popular flashing material, but other materials may be used.
Spotting signs of faulty flashing can save time and money if addressed early.
Without a proper roof flashing system, your entire house is susceptible to some pretty scary stuff. We’re talking about leaks and water damage, mold, rotting, and even pest infestations. So, what is roof flashing, and how can you tell if yours needs to be replaced?
Simply put, roof flashing uses a waterproof material (usually steel) to direct water away from the most vulnerable areas of your roof.
Unless you have adequate roofing experience, we do not recommend messing with your roof flashing as a DIY project. You’ll need to bring in a local roofing professional to help you make repairs to your flashing system.
However, it’s still useful to know what roof flashing is and how it works. The more you understand what to look for, the sooner you can identify potential issues—ultimately preventing costly, severe damage.
Purpose of Roof Flashing
A roof flashing system is designed to direct the flow of water off a roof, bypassing the areas that are the most susceptible to water damage.
More specifically, roof flashing materials are strategically placed to close corners and crevices where water could seep in without it (think chimneys, skylights, vents, etc.).
Types of Roof Flashing
Though the overarching idea of roof flashing is the same, there are different types that fit some situations better than others. Here are seven common types of roof flashing you should know:
1. Base Flashing
Base flashing helps prevent water damage at vertical-to-horizontal intersections on a roof where the roof meets a vertical wall juncture. Base flashing is installed underneath siding and shingles, so it's not easily seen.
2. Step Flashing
Step flashing involves “L” shaped pieces of flashing material that are installed along the corner where the roof meets a sidewall. This type of flashing is partly visible, so homeowners may choose a more expensive material to better match their home’s exterior.
3. Counter Flashing
Counter flashing is placed either above or opposite of base flashing. It’s most commonly used between the roof’s surface and a chimney or a brick wall. Its purpose is to protect the base flashing.
The most effective way to install counter flashing on a chimney is actually while the chimney itself is being built. However, you can still add counter flashing to an already existing brick structure.
4. Continuous Flashing (aka Apron Flashing)
Continuous or apron flashing is a long piece of flashing that reroutes water from vertical walls and sloped roofs into a gutter.
5. Valley Flashing
Valley flashing involves using flashing materials to line the dip where two sides of a roof come together and form a valley. This helps direct running water off of the roof and into the gutters.
6. Kickout Flashing (aka Diverter Flashing)
Kickout flashing is needed when a gutter ends against a sidewall. This kind of flashing helps prevent water from running down the sidewall and diverts it into the gutters instead.
7. Drip Edge
Drip edge flashing is placed around the edges of a roof to prevent water from dripping behind the gutters and rotting out the roof in the process.
8. Skylight Flashing
Skylight flashing protects the junction where the skylight meets the roof and uses both step flashing and counterflashing. Some skylights offer or require their own flashing kits to ensure a snug fit and proper seal to reduce the chance of leaks.
Types of Roof Flashing Material
Steel is the most common roof flashing material, but you can use other materials depending on your project.
Aluminum is a lightweight material that is easy for roofers to form into the correct shape. Unfortunately, aluminum can corrode when in contact with concrete or masonry, so in order for it to stand up to these applications, it must be coated.
Copper flashing can also be shaped easily, holds up well to soldering, and is very durable. Copper is more expensive than other flashing materials and will naturally patina over time.
Steel is the most popular option for roof flashing. It can be shaped into the correct form and both stainless and galvanized steel are corrosion-resistant.
Signs of Flashing Issues
Unless you’re an experienced roofing professional, it may be difficult to notice when your flashing system needs to be replaced, but you can look out for these easy-to-spot signs:
Noticeable corrosion and rust in flashing and gutters
Curling or broken shingles
Patches on the roof
Water damage in the attic or interior walls (water stains, mold, etc.)
Spotting signs of flashing issues and addressing them early can help prevent damage to the roof and cost less than the full roof replacement cost.
How to Repair Flashing
Roof flashing is a tricky task. Even the smallest spaces that are missed or not properly sealed can be an expensive problem later on down the road. If you think that you may have water damage issues due to faulty flashing, it’s best to hire a local roofing professional for an inspection.
Caroline Gilbert contributed to this article.