What Is Roof Flashing And How To Do It Properly

What Is Roof Flashing And How To Do It Properly?


February 28, 2022

Rainwater can be a big problem for your roof.

While you might think you just need a gutter system to be installed on your roof so that you can keep water away from its structures, this is not enough. You also need to ensure you have roof flashing.

Why is roof flashing so important?

Roof flashing helps to push water into the gutters so that it can reach the ground instead of accumulating on the roof where it can cause problems such as ice dams, mold, and mildew.

Let’s explore everything you need to know about roof flashing. We’ll also give you tips on how to install it properly to keep your roof in excellent condition. 

What Is Roof Flashing? 

What Is Roof Flashing And How To Do It Properly

Roof flashing is a strip of metal that’s installed on the roof to direct rainwater away from areas of your roof, such as your walls and chimney, to ensure that you prevent water from accumulating on the roof and damaging its structure. This also protects your home against water damage. 

Types Of Roof Flashing 

There are many different types of roof flashing to strengthen your roof structure. These include the following: 

  • Continuous flashing. This is called apron flashing and it’s a single, long piece of metal that diverts water down to the shingles. It covers a joint, such as where the roof meets a wall of siding.
  • Base flashing. This includes two pieces of flashing that is used for roof structures such as chimneys. Base flashing guarantees that water meets a flashing surface wherever it falls so that it will be transported downard. 
  • Counter flashing. This type of flashing is placed on the opposite side of, or above, base flashing. 
  • Step flashing. This is flashing that’s rectangular in shape. It’s bent in the middle and is used for wall flashing. It has a scale-like design so that the pieces of flashing overlap each other and slip underneath the shingles. It’s mainly used where a wall meets the roof. 
  • Valley flashing. Valleys on the roof need to have metal flashing installed on them to protect them. Valleys are a part of the roof that accumulate a lot of water.
  • Skylight flashing. This type of flashing is usually purchased with your new skylight. It protects the skylight and surrounding roof from water damage. If it’s not provided, you’ll have to purchase the skylight flashing separately. 
  • Kickout flashing. This is placed at the start of gutters to draw water away from the wall so that it can enter the gutters properly. 
  • Drip edge flashing. This is flashing that’s placed on the roof edge. It draws water off the roof without it splashing onto the home’s walls or causing any leaks that can result in water damage. 

What Metals Are Roof Flashing Made Of? 

There are different metals that can be used to make roof flashing. Let’s take a look at their pros and cons.


Aluminum is easy to shape and use, especially because it’s lightweight. Aluminum needs to be coated if it’s used with masonry and concrete, though, and this is because aluminum reacts with alkaline surfaces. If you live in a coastal area, aluminum flashing needs to be coated to prevent corrosion from the moisture in the air.


Another popular metal for flashing is copper. It’s flexible and easy to shape, and can be soldered without a problem. Copper is durable, but it does develop a patina which might not be to everyone’s tastes.


Steel is the go-to metal used to make flashing for the roof. This is not just because of how durable it is but it’s flexible, malleable, and can be made resistant to corrosion by being galvanized. 

What about plastic flashing?

You can find some flashing products that are made out of plastic, but this is not usually recommended. Although plastic is more affordable than metal flashing, it degrades over time when exposed to direct sunlight so it won’t last as long as metal flashing.  

Types Of Roof Flashing Sealant 

What Is Roof Flashing And How To Do It Properly

Some roofing professionals will use nails when installing flashing, but this isn’t always possible. It can cause damage to the roofing structure, so they rely on sealants instead. There are different types of flashing sealants available, such as the following.

Butyl sealant

This is a popular type of sealant used in the construction industry because it’s readily available and cheap to buy. You can buy this sealant in a plastic tube or as a tape-roll product. While it works, it’s not as flexible as other sealant products you can buy. 

Silicone sealant

Silicone sealants work well to seal flashing effectively because they cure when exposed to moisture. They are clear and can therefore be used with lots of colorful building materials without standing out like a sore thumb. However, they can also be pigmented if you want to match the silicone to the flashing. What’s great about silicone sealants is that they cure at a fast rate.

Polyurethane sealant 

This is another good choice for sealants. It comes in a variety of colors so you can match it to your roof. It doesn’t take a long time to set, which makes it user-friendly.

However, if you live in an area where temperatures are extreme and fluctuate a lot, or you experience intense weather patterns, this sealant can deteriorate at a faster rate. This is a versatile sealant that will accommodate a variety of flashing materials. 

Roofing cement 

Roofing cement contains a blend of mineral spirits, asphalt, plasticizers, and reinforcing fibers. This makes it suitable for a variety of dry and wet applications, which is why it’s such an essential item roofing contractors should have in their possession. Roofing cement can be used to seal down flashing or shingles. It’s strongly adhesive and works well to prevent leaks.


Rubber makes sense for use as a roofing sealant because it is waterproof. It can be water-based to make it easy to apply so it’s not too thick. It provides good protection against sun and rain. Rubber sealants are not only durable but also flexible, which means they work well to resist crumbling and cracking, even when dealt with extreme temperatures. 

Modified polyether sealant

This sealant hasn’t been around for as long as some other sealants, but it’s made from modified silicone which has many advantages. These include how you’re able to apply the flashing sealant with a gun, which makes your roofing tasks go faster. Polyether is resilient and can be used in very cold temperatures. 

How To Install Roof Flashing

What Is Roof Flashing And How To Do It Properly

Whether you want to DIY your roof flashing installation or you’re leaving it up to the pros but you’re interested in knowing how it gets applied to your roof, here’s what you need to know about installing flashing on a new roof system. 

  1. You will have to start by installing underlayment beneath your roof shingles. This is because the shingles have to overlay the flashing. 
  2. Start with installing corner flashing as this needs to be laid down first so that you’ll be able to install the kickout or step flashing from the bottom all the way up. The kickout flashing will be installed at the base of the roof and kept in place with roof cement. 
  3. Place the first shingle so that it sits on the starter strip and the kickout flashing will be secured with the roofing cement and nails. Ensure that the nails are placed high up on the shingles so that they will be covered by the next piece of flashing. 
  4. Place the shingles over kickout flashing, then keep going until you reach the top of the roof.
  5. Cut and fit the flashing and shingles to the peak of your roof. They both have to be bent over the peak so that they are curved. This will ensure that the joints are watertight. 
  6. The flashing needs to be covered halfway by shingles. The other half will be covered by siding. 

How To Repair Roof Flashing Leaks

If your flashing is damaged and leaking, you will have to repair it. You can do this easily if the area of damage is small, such as if the flashing has a corroded spot or there’s a small hole in it.

You’ll have to add sealant, such as roofing cement, to the area to create a plug. Then, you can patch the holes with a patch made of the same material as the flashing you wish to repair.

Make sure you first sand down the area around the hole you want to repair with some sandpaper and clean it well. Then, cut the patch so that it’s a bit larger than the size of the hole. Set it with roofing cement and cover the patch with more cement so that it gets properly sealed in. 

If you have flashing that is more damaged, you will have to replace it. To do this, several shingle rows and the old flashing will have to be removed, so calling a professional might be the best idea. 

Tips For Maintaining Your Roof Flashing 

What Is Roof Flashing And How To Do It Properly

To ensure your flashing has a longer lifespan, you should keep it in good condition. Here are some maintenance tips to follow.

  • Regularly check the flashing for any crumbling or cracks. Repairing small damage will be much easier in this way.
  • If your flashing is new, it can be very shiny so you want to paint it to make it blend in with the roof. This can also prevent corrosion from the flashing being exposed to sun and rain.
  • Remove any debris, flaking paint, and rust with a stiff brush. Just make sure that if you’re using a solvent to clean the flashing you don’t let it come into contact with your asphalt shingles otherwise it can damage them.
  • A good idea for keeping your flashing in good condition is to apply a zinc-based primer before spraying on two light coats of metal paint. This inhibits rust from forming. 

Do You Need To Replace Roof Flashing? 

You might not be sure if you need to replace your roof flashing. The most important thing is to look at the condition of your flashing. If it’s cracked or damaged in any other way, it’s a good idea to go ahead and replace it.

If your flashing looks dirty, this isn’t a good enough reason to replace it. You can clean it to give it a new lease on life. If it’s very old, however, then it’s probably a good move to replace it. A smart time when to do so is if you’re replacing other roof components, because then replacing old flashing at the same time can be advantageous. 

Related Questions 

How long does roof flashing last?

Generally, roof flashing can last for between 20 and 35 years. 

Can you reuse roof flashing? 

You can sometimes re-use flashing, but it has to be in very good condition otherwise it will just be a waste of time and a possible liability for your roof. 


Roof flashing is an important piece of metal your roof needs to protect it against water damage.

If you’re not sure how to properly install roof flashing, we’ve given you all the steps to follow so that you can do so successfully. We’ve also looked at how to repair roof flashing and how to tell when it’s time to replace it.



James Weldon is a professional roofing contractor with many years of experience on the job. He does not only handle large projects and provide excellent services for his company’s many clients; James Weldon also dedicates his spare time to teaching others useful tricks of the trade. Using BuildCampus as an avenue to reach many roofers and aspiring roofing contractors, James Weldon continues to provide high-quality educational posts and buying recommendations for anyone who visits the website.