Roof flashing is a thin metal barrier, usually a thin sheet of metal, that is installed at the weak points where your roof meets vertical surfaces, some sort of penetration, or where it goes around a corner. This thin metal sheet is a critical component in waterproofing, acting as a protective barrier against water intrusion.
After years of doing roof work, we’ll tell you that proper flashing installation is the difference between a roof that will last decades and one that starts leaking within a few years. Roof flashing is important because it protects roof structures from water intrusion, prevents leaks, and extends the lifespan of your roof by sealing vulnerable areas like chimneys, valleys, and where walls meet the roof.
Drip edge and drip edge flashing are roof flashing types that are installed along the roof’s edge to keep water running down to the gutters and prevent water from getting in through the roof. Selecting the right roof flashing types for each application is crucial to ensure effective protection against water damage. When getting your flashing installed, a good roofer will make sure it’s done right so you don’t get water leaks.
To prevent leaks, it’s essential to install flashing correctly at all vulnerable points, including the roof’s edge, roof’s surface, and around roof penetrations such as vents, chimneys, and skylights. Flashing is usually put in where shingles butt up against vertical walls, chimneys, or other vertical surfaces, along the roof, or around roof features like vents and skylights. Some specific types of flashing, like base flashing and skylight flashing, are used for features like chimneys and skylights.
When choosing your roofing materials, you have to think about what will work with the flashing, because some materials can rust if they come into contact with pressure-treated wood, which can accelerate the corrosion of galvanized steel flashing. Asphalt cement is often used to secure and seal flashing parts, so they get stuck well into the roof deck and stop leaks. Plastic flashing is a non-metal alternative, valued for its resistance to corrosion, but it may have limitations in durability depending on environmental conditions. Sheet metal is also commonly used for custom flashing pieces due to its strength and ability to be shaped for specific needs.
The main thing that flashing does is create a watertight seal at the tricky spots where different roof parts meet up. Your roof’s flashing is a vital part of the roof, and it’s what prevents leaks where different parts of the roof meet, protecting the roof structures from water damage. Whether you’re doing a new roof, fixing an old one, or just building a new house, knowing about the different types of roof flashing and what they do will help you avoid having to fix roof leaks.
The Importance of Roof Flashing
Lots of first time homeowners look up what is roof flashing because it’s one of the most important things to keep water from getting into your house. A decent roof flashing installation will save you a ton of money down the line. In simple terms, roof flashing is a thin material, usually metal, but sometimes vinyl or plastic, that gets put in to direct water away from the parts of the roof that are most vulnerable.
When you’re deciding what to do, you’ll find there are lots of different kinds of roof flashing, all designed for specific parts of the roof and climates. Metal flashing is a popular choice because it’s good and durable, and most people go with galvanized steel, aluminum or copper. If you want something that will last a long time, copper is a good choice, especially if you have a fancy or an old house.
Aluminum is lightweight and won’t rust, so it’s a good fit for lots of modern roofs. For all our roofing jobs, our guys will help you pick out the best flashing for your home, so you can be sure it’s well protected.
Step Flashing
Step flashing is small, L-shaped metal piece that you install in an alternating pattern with the roof shingles, usually along walls and chimneys. Each piece is about 10 inches long and a bit wider than the shingles on your roof. The “step” installation pattern makes overlapping layers, so each piece covers the one below it, just like how the shingles overlap.
The way we do step flashing is to install it so that each piece extends way under the shingles and up the side wall, to make sure that water runs away from the spot. This is the most reliable way to stop water from running down the side and getting into the roof.
In really windy or stormy weather, there is a risk of dislodged flashing if it’s not attached to the roof deck properly. So we make sure to use plenty of fasteners to keep it in place and keep the water out. However, we have noticed that thermal expansion and contraction can have quite an impact on the metal flashing material over time, particularly with longer pieces. This is why, in many cases, we prefer apron flashing over step flashing for specific applications where the ongoing protection outweighs those thermal movement worries, like shed dormers or long headwall jobs.
Apron Flashing
Apron flashing, also called headwall flashing, is L-shaped metal flashing installed as one continuous piece at roof-wall intersections. Unlike step flashing’s individual pieces, apron flashing can extend up to 14 feet long to cover large roof penetrations like chimneys or dormers. During installation, one leg goes under the roof shingles while the other extends up the vertical wall.
Most homeowners prefer apron flashing for its clean appearance and strong protection against water intrusion, especially on longer wall runs where multiple step flashing pieces might create more potential failure points. The continuous design eliminates seams that could allow water penetration over time.
Valley Flashing
Valley flashing is crucial for protecting that critical spot where two roof slopes meet and funnel water downwards with a lot of force, requiring a rock solid waterproofing solution. From our experience, roof valleys are among the heaviest water loads you’ll find on any roof surface, and proper valley flashing installation is vital for stopping roof leaks dead in their tracks.
We usually install valley flashing in two main ways: open valley flashing, where the metal flashing is left visible, and closed valley methods, where shingles cover the valley. The choice depends on your roofing material, roof pitch, and how much you care about looks. Sometimes, with architectural shingles, we go for the closed valley method, but we usually recommend open roof valleys with metal flashing for maximum water-shedding capacity.
When we’re installing valley flashing, we pay close attention to proper underlayment and ice-and-water shield placement underneath the metal flashing. From years of experience, valley flashing failures often result from a subpar roof deck prep or the wrong flashing material being picked for the local climate, especially in areas prone to ice dams.
Counter Flashing
Counter flashing is the secondary layer of protection that gets installed over step flashing on walls and chimneys. Unlike hidden step flashing under the shingles, which is low profile, this one’s visible on the roof and gets embedded into the mortar joints of masonry walls or chimneys.
It’s a two-part system that creates redundant protection where the counter flashing overlaps and covers the step flashing underneath. For our reroofing projects, we embed the counter flashing in existing mortar joints and seal it up with the right roofing cement for a watertight seal.
It’s also worth noting that the timing of the counter flashing installation is pretty important, and it’s best achieved during initial construction. Although we can retrofit it during roof replacement or chimney repairs, it’s not our preferred approach. During our maintenance inspections, we are always on the lookout for signs of counter flashing failure, like loose mortar, displaced flashing, or water stains that show the roof’s flashing system needs some TLC.
Chimney Flashing
Chimney flashing is a specialized type of roof flashing designed to protect the critical intersection where your chimney meets the roof surface. Chimneys can feel like the weak link of your roof as they stick right through your protective barrier and create complex joints that practically invite water intrusion if they aren’t properly sealed.
Vent pipes are another common roof penetration that requires careful flashing installation to prevent leaks. Your chimney flashing is usually made of metal like galvanized steel, aluminum, or copper, and when it’s installed correctly around the base of your chimney, up the sides, and sometimes over the top, it creates a continuous, watertight seal that guards your home against the elements.
You can’t afford to overlook the proper installation of your chimney flashing. The process often involves a combination of step flashing and counter flashing working in harmony to ensure that water is directed away from your chimney and can’t seep into your roof deck or interior walls. Each piece needs to be securely fastened and sealed, with special attention paid to those joints and corners where leaks are most likely to pop up and wreak havoc on your home.
Materials and Installation Considerations
We’ve worked with a range of roof flashing materials, each offering its own set of benefits and lifespans. Galvanized steel is still the most common choice due to its balance of affordability and durability, typically lasting 20-40 years depending on climate conditions. We often recommend aluminum flashing for its lighter weight and corrosion resistance, though it needs proper coating when in contact with masonry materials.
For historic homes, we often suggest copper flashing due to its 60+ year lifespan and attractive patina development. Copper roof systems particularly benefit from matching copper flashing materials to maintain both performance and aesthetic consistency.
Metal flashing materials generally require a 26-gauge minimum thickness to meet building codes, though we prefer slightly thicker materials in harsh climates. When installing roof flashing, we use the right sealants for different flashing types and ensure they are all fastened correctly, which means nails are going into the roof deck and never into the vertical surfaces where thermal movement could cause failures.
When reroofing, it’s essential to evaluate whether the existing flashing should also be replaced when the roof is replaced to ensure compatibility and prevent future issues. Experienced roofing contractors will recommend replacing flashing as needed during a roof replacement to ensure long-term protection and prevent leaks.
If flashing is found to be damaged or deteriorated, it’s important to repair roof flashing promptly to prevent water intrusion and protect the underlying structure.
When you install roof flashing, consider thermal bridging concerns and how the metal flashing affects the roof system’s energy efficiency. Proper installation techniques and material selection based on your local climate, budget, and aesthetic preferences is key to getting long term performance.
Maintenance and Repair
You probably already know that keeping your roof flashing in top shape is just as vital as getting the initial installation right when it comes to stopping those dreaded roof leaks & extending the life of your roofing system.
Faulty flashing is a common cause of roof leaks and water damage, so it should be promptly addressed during inspections. Over time, you might start to notice that flashing is getting damaged, corroded, or dislodged, which is just a natural result of weather and temperature changes. That’s why regular inspections at least once a year and after some major storms is a must for your peace of mind. You should be on the lookout for signs of rust, cracks, loose fasteners or gaps in the flashing, especially around those vulnerable roof penetrations, valleys, and edges where your roof works the hardest to keep you safe.
If we notice any issues while inspecting your roof, we’ll recommend prompt repairs to keep those roof leaks at bay and prevent more extensive water damage down the line. Oftentimes, our roof repairs include re-sealing joints with roofing cement, replacing sections of damaged flashing, or reattaching loose pieces to get that snug, protective fit your home deserves. Sometimes, especially with older roofs, we might need to replace entire sections of flashing to get that watertight seal back.
Choosing the Right Flashing for Your Roof
Choosing the right roof flashing depends on your roof pitch, your local weather and your roof’s specific architectural features. For steep-slope applications with asphalt shingles, we generally use galvanized steel or aluminum flashing with step flashing techniques around most roof penetrations—and for homeowners interested in metal roofs, these options provide strong and durable solutions.
Metal roof systems need specialized flashing materials and techniques that are different from traditional shingle jobs. When we do a roof replacement, we have to figure out if the existing flashing can stay or needs to be replaced based on its condition, age and whether it’s compatible with the new roof.
Getting proper flashing installed in the first place pays off in the long run and protects against all that expensive water damage that’ll far exceed the cost of the flashing itself. If you work with NearMe Roofing Company, you can rest assured knowing you’re partnering with a licensed and insured roofer and you’re in compliance with local building code requirements.
In the long run, annual roof maintenance, regular inspections, and proper installation will determine how well your flashing will perform. From our experience installing roofs and flashing all over the Puget Sound region in Washington, most roof flashing problems creep up over time and can be prevented with regular maintenance. Getting to those minor issues is critical before they turn into major leaks that’ll compromise the integrity of your whole roof system.
