The roof is the first line of defense for your home, but even it can be vulnerable to the elements, especially rain. This is why the flashing is such an important component of any roof.

What Is Flashing?

Flashing helps to prevent water leaks by directing the flow of rain water around openings in the roof. They ensure that instead of leaking into your home, water runs off down the roof and into your gutter system.

Flashing is available in a number of different materials, including:

  • Aluminum. Aluminum flashing is durable and cost-friendly. However, it can corrode if it’s in contact with concrete or fiber cement siding.
  • Copper. Copper is more difficult to form than aluminum and more costly, but it’s incredibly durable. It’s also compatible with some of the newer types of wood preservatives used on roofing.
  • Galvanized Steel. Although less expensive than other flashing materials, it’s not as durable either.
  • Lead. Lead is often used for chimney flashing because of how soft and easy to bend it is. It’s also quite durable.
  • PVC. PVC is inert and relatively easy to work with.

Most contractors will custom build flashing in order to fit specific areas on your roof. A flashing that doesn’t fit properly is going to do a poor job keeping water out.

Once the flashing is installed, the edges will be sealed using a waterproof sealant. Flashing made out of aluminum or galvanized steel is secured in place using nails.

Where Is Flashing Used?

The following are some of the areas on the roof that generally need flashing in order to protect your home against leaks, which can result in extensive water damage:

Dormer Windows.

Dormer windows are especially vulnerable to the elements because of the way they jut out from the roof.

Flashing squares are often placed between every row of roofing material. It can also be used as a strip of flashing that runs around the dormer and beneath the roofing material.


When skylights are built into a roof, they are raised with a wood curb to provide enough room for flashing material. If you are replacing your home’s roof, you may need to raise the skylight in order to properly install flashing.

Some skylights may come with flashing already built in, but these types of skylights may still require additional flashing.


Flashing strips are typically used for the chimney. These strips are usually made out of metal or PVC flashing and cover the joint between the chimney and the roof.

The flashing is overlapped by the edges of the roofing material on one side and cap flashing on the other. The cap flashing is attached to the chimney’s mortar joints.


Vents are a necessary feature in any roof. If the vent is already installed, then the height of the flashing detail may need to be altered around the vent.

If you’re installing a new vent, then you’re going to need to cut a clean hole in the roofing material before installing the flashing. There are two kinds of vents – hood vents and pipe vents.

For hood vents, a flashing flange will have to be slipped under the shingles above the vent. For pipe vents, pipe flashing will need to be slid over the pipe once it’s installed.

Valleys. If you have a sloped roof, then you need to add flashing to the valleys. The valleys, which is the space where two planes of a roof meet, are notorious for developing leaks.

Because roof flashing is such an important part of your roof, ensuring that it’s properly installed and maintained is incredibly important to avoid future roof repair or replacements.