Roof flashing — a flat, thin sheet of metal — is essential to any residential home. It seals off the roof system’s perimeter, leading rain water away from any openings and cracks to prevent leaks.
Roof flashing encompasses many types, from the chimney flashing to valley and base flashing. On average, roof flashing should last about 25 years, if not longer. If you’re looking to install your own roof flashing, be sure to install corner flashing first, leave room for potential expansion, and seal the flashing twice.
In our overview guide on roof flashing types, we’ll go over what roof flashing actually is, the most common types of roof flashing, the life expectancy of various roof flashing types, as well as must-know installation tips for those looking to try their hand at roof flashing.
Let’s start with the basics: What does “roof flashing” actually mean?
What Is Roof Flashing?
Roof flashing is a thin, flat piece of metal designed to help make the perimeter of roofing systems waterproof.
Thanks to roof flashing, water is channeled away from the joints and seams of the roof, which stops water from leaking in through any cracks or openings during a storm. Contractors usually install roof flashing underneath the shingles but on top of the underlayment for a shingled roof. On the other hand, flashing for metal roofs is installed directly on top of the panels.
The main responsibility of roof flashing is to make sure your house doesn’t experience any leaks when it rains. It also helps the roofing system keep moisture from accumulating.
However, roof flashing is important in many areas of your home, from the valley of your sloped roof to your home’s chimney.
Types of Roof Flashing
Because roof flashing aims to prevent water from leaking through any cracks and openings that could be on your roof, there are a few areas of the roof that need special consideration as they’re more prone to leaks.
For roof flashing to work, it has to be installed correctly by a contractor. If the flashing isn’t installed properly, not only could water leak into your home, but other problems could crop up too, like term issues like roof deterioration.
The most common types of specialty roof flashing include:
- Chimney flashing
- Step flashing
- Headwall flashing
- Valley flashing
- Base flashing
- Continuous flashing
- Gutter apron flashing
Chimney Flashing
Chances are, you’ve seen chimney flashing before. It often stands out against red brick. Because chimneys in particular are such vulnerable spots for water leaks, chimney flashing is critical in preventing unwanted water seeping into your home.
Using metal sheets that are usually cut into custom sizes based on the shape of the chimney, contractors make sure to target the areas around the chimney that are extra prone to water leaks.
Chimney flashing uses the same techniques as both step and headwall flashing, which we’ll describe in detail below.
Step Flashing
When a sloped roof intersects with a vertical sidewall, homeowners will want step flashing. Step flashing uses sheets of metal that are then placed over each other and are interlinked with the material your roof is made of. The individual metal sheets that are used in step flashing usually run 4 inches by 4 inches by 8 inches.
This type of roof flashing makes sure that moisture and water can’t seep into the roof-to-wall joint.
Step flashing can also be complemented by counter flashing.
Headwall Flashing (AKA Wall Flashing)
Headwall flashing — also known as “wall flashing” — is a kind of flashing used when vertical headwalls meet the upper end of a roof section. All these names refer to the same thing.
With headwall flashing, contractors use metal that’s typically around 10 feet long and “L” shaped. They’ll cut the flashing to fit the specific section of wall that’s being worked on, so it’ll be custom-fit.
Headwall flashing works by channeling water down the wall, onto the roof, to prevent any water leaks. Depending on what your home and roof system looks like and if it has a brick headwall, headwall flashing could be complemented by counter flashing.
To secure headwall flashing to other types of wall materials — such as stucco, brick, or stone — contractors utilize counter flashing, since the metal headwall flashing can’t be tucked into the wall. To install counter flashing, contractors use sealants and mortar fasteners, both of which work to seal the wall and discourage any leaks.
Valley Flashing
Valley flashing is a common type of flashing protection for the valleys of roofs. If there’s an angle change on a roof system, valley flashing is used.
Valleys on the majority of shingle roofs are typically protected using an ice and water shield, which is a self-adhering piece that offers protection; however, contractors can add metal valley flashing to make sure to keep out both moisture accumulation and water.
Contractors can install valley flashing in a number of ways. One of the most common methods for installation is the open, no-cut valley flashing method.
The contractor handling the job will usually start by installing the ice and water shield in the middle of the valley if there isn’t already one there.
Next, they’ll put in the metal valley liner before adding shingles alongside the valley. These shingles stop water from being channeled into the wrong places. The goal of a roof system is to direct water down to the ground, and valley flashing aids in this effort.
Base Flashing
Base flashing is a type of roof flashing that’s connected to the deck to channel the rain water onto the roof system’s covering. Base flashing seals a roof at vertical intersections using a membrane material. For example, you might use base flashing where the roof curb and roof wall meet.
Base flashing is meant to specifically protect the roof deck from water drainage and moisture accumulation.
Continuous Flashing
Continuous flashing is one long piece of flashing that protects the area where a vertical wall meets the roof. Continuous flashing directs water down to the shingles of the roof.
Although homeowners can leave the flashing exposed, they can also direct the contractor working the job to attach what’s called a “beauty strip” — a strip of asphalt shingle material — to make the continuous flashing less noticeable from the street.
Usually, continuous flashing is installed below the shingles of a roof system.
Gutter Apron Flashing
With gutter apron flashing, a contractor will install flashing alongside the roof system’s gutter line. The gutter line is where the gutter meets the roof system. Where they intersect, there’s a small gap between the roof sheathing and the fascia trim board.
Gutter apron flashing uses something called a drip edge — a piece on the metal designed to prevent rain water from washing onto other parts of the home. This lip of metal also makes the flashing more durable.
As the name suggests, this kind of flashing channels water into the gutters, where it can safely maneuver down toward the ground. Gutter apron flashing also prevents animals and insects from getting into your attic and gives your roof an extra layer of protection from the outside elements.
To install gutter flashing, the contractor will secure the flashing to the roof system’s sheathing. Typically, ice and water shield is added next, along with a starter course of shingles. Once all of those items are secured, the contractor can add the rest of the shingle courses or rows.
In addition to the aforementioned common types of roof flashing, other types of flashing you might hear about include:
- Penetration flashing
- Skylight flashing
- Drip edge flashing
- Cap metal flashing
- Vent pipe flashing
- Two-part flashing
- Kickout flashing
But how long does roof flashing last?
What’s the Life Expectancy of Roof Flashing?
On average, the life expectancy of roof flashing is about 25 years or longer. The most common range for a roof flashing lifespan is 20 to 35 years. When installed properly, roof flashing should reach about 40 years of age.
Below is a table that compares a few different types of roof flashings and materials with their respective estimated life expectancy.
| Type of Roof Flashing and Material | Estimated Life Expectancy |
| Elastomeric coating | 10 years |
| Skylight and light tube | 14 years |
| Gutter flashing with vinyl | 15 years |
| Pipe boots | 20 years |
| Gutter flashing with aluminum | 25 years |
| An average roof flashing | 25 years |
| Gutter flashing with copper | 50 years (or more) |
How Much Does Roof Flashing Cost?
On average, you can expect to spend anywhere between $15 to $25 per linear foot on roof flashing, including both the material used to seal it and the actual flashing itself. For a complete roof flashing, expect to pay a couple hundred, if not more.
Factors that affect a roof flashing’s cost include materials, labor costs, whether it’s a repair or a full replacement, the size of the area, and the initial inspection cost, among others.
Below is a helpful table on roof flashing cost estimates, including the roof flashing type and whether it’s a repair or a total replacement. Keep in mind that these are only estimates — the cost to repair or replace your roof flashing could vary.
| Roof Flashing Type | Costs for a Repair | Costs for a Total Replacement |
| Drip edge flashing | $1 to $2 per linear foot | $1 to $2 per linear foot |
| Flat roof cement flashing | $10 to $25 per square foot | $10 to $25 per square foot |
| Chimney flashing | $200 to $500 total | $350 to $1,500 total |
| Skylight flashing | $200 to $500 total | $700 to $1,500 total |
| Valley flashing | N/A | $350 to $1,000 total |
| Vents flashing | N/A | $200 to $500 total |
Roof Flashing Installation Tips
Although the majority of roofing experts will cut their own roof flashing to custom fit particular sections, you can also find pre-cut roof flashing sheets available for purchase.
If you’re installing roof flashing yourself, make sure you’re buying the right pre-made flashing. Some pre-cut flashings aren’t meant to be installed on roofs and could potentially break or damage your roof. For example, you wouldn’t want cap flashing or head flashing for your roof; those are better suited to prevent water from coming in through windows and doors.
Here are some quick, must-know installation tips if you plan on tackling your roof flashing job yourself.
Install Corner Flashing First
Corner flashing, which is usually placed around corners or walls that come out from the top of the roof, should always be installed first. That way, you can build your step flashing or kick out flashing on top of it.
Even though the ideal is to use what’s known as a prefabricated corner, keep in mind that this will need to align with the slope of your roof exactly or the flashing will fail. If flashing fails, you’ll experience leaks, moisture accumulation, and water from seeping into other places, which equates to long-term damage.
Leave Room For Expansion
Although you might not realize it, it’s absolutely critical to leave room for expansion when installing roof flashing yourself.
In the changing seasons, your house will actually expand and contract based on temperature and climate. Ideally, flashing can flex along with the expansion. However, if installed incorrectly, the roof flashing can warp or even break, letting both water and moisture in. This can lead to some pretty serious leaks and — you guessed it — long term damage to your roofing system and house. Today, most long roof flashing pieces have expansion joints that are built-in, meaning they move alongside the home as it expands or contracts.
When installing roof flashing, be mindful to leave room for contraction and expansion, especially for areas like the J-channel, starter strip pieces, and between the corners.
Seal the Flashing Twice
If you’re curious as to why you’d want to seal the flashing twice, think back to the last time you experienced a leak coming from the roof. That’s why.
Roof flashing that isn’t properly sealed is the number one cause of roof leaks. After all, the seal is supposed to ensure no water can seep through cracks, corners, or openings. By sealing the flashing twice, you’re taking extra care to make sure it’s watertight and will stand up to heavy rainwater and other moisture.
The importance of roof flashing can’t be emphasized enough. A handful of roof flashing types, each crucial in their respective ways, are responsible for ensuring your house is free from rainwater, leaks from ponding water, and moisture accumulation.
You can expect your roof flashing to last around three decades, if not longer. Its lifespan will completely depend on factors like the type of flashing, the material, and of course, whether or not it was installed properly.
Remember, if you’re tackling the roof flashing installation yourself, start with the corner flashing, always seal it twice, and leave room for expansion.
Ruben has a diverse background in the home services industry, with experience running a construction company, a kitchen and bath showroom, and a moving and relocation company. This breadth of experience has provided him with a wealth of knowledge and expertise in various areas of home improvement in general and specifically in the heating and plumbing niche.