What Is Roof Flashing? Understand The Types & Useful Techniques

Home Tips

Do you ever find out that after a few months of roof installation, the roof has several leaks and broken tiles on it? If your answer is “Yes”, then you should consider doing roof flashing immediately. 

What is roof flashing? This article will give you a detailed explanation about it, and some advice about reinforcing your roof to make it last longer. 

What Is Roof Flashing?

Roof flashing is a roll of thin metal, which is placed under the shingles or between the joints where the roof’s surface intersects with a projection such as a chimney, dormer wall,… 

Roof flashing is resistant to moisture and strong winds so that it can prevent the roof from water damage through leaks and reinforce roof tiles.

The most popular materials used to make roof flashing are galvanized steel, copper, and aluminum. Galvanized steel is often used in buildings, while aluminum is suitable for a do-it-yourself project because of its flexibility to bend, and copper is used for copper roofs. 

5 Types Of Roof Flashing

Based on the area that you are going to apply roof flashing, there are various types of it to choose from:

1. Valley flashing

A roof valley is a V-shaped place where 2 roof slopes meet. As its name suggests, the roof valley is where the raindrop drips down and gradually penetrates the roof surface to create leaks.

what is roof flashing

To solve that problem, we need valley flashing. The metal sheet will be placed under the shingles, keeping each roof slope from touching each other. By doing that, water will run across the edge of the roof slope, into the flashing, and down to the rain gutter, with minimal damage to the roof valley.  

Maybe you are also interested in: How to Fix A Leaking Roof from The Inside?

2. Chimney flashing 

Flashing is sealed between shingle courses running along with the chimney. Along the sides, counter flashing is mortared into the stone courses and goes down over the top of the step flashing.

Besides, flashing is also mortared into the chimney’s front side at the end of the roof slope and on top of the next shingles, so that the rain will run across that way and cannot damage the chimney. 

3. Vent flashing 

Vent flashing prevents water from accumulating around the vents and pipes. They can be a plumbing vent, hood vent, or pipe from the woodstove. The metal flashing has a central spout opening, which is made of these 2 materials: 

  • Rubber: So that it wraps around the pipes and creates a water-resistant seal.
  • Metal: So it can cover the vent top.

The flashing has a metal square piece at the bottom. To install it, the central part will slip over the pipe or vent, underneath the roofing and run along with the top and back edge (the front edge does not need covering). This allows water to run out of the vent’s opening. 

Read more: Can You Paint A Metal Roof? 3 Steps To Upgrade Your House Appearance

4. Drip edge flashing

Drip edge flashing is the L-shaped sheets made of metal, installed at the edge of the roof. They play the role of directing water away from the fascia (an area that suffers water damage directly from rain) and into the gutter. 

Also, wrap flashing around the rake edges, so that the outmost shingles will not be blown away by strong winds.

5. Skylight flashing

For skylights, a continuous piece of flashing is used to seal along the base to the top to keep water away from them. Skylights often knob out from the roof, so it would be easy for you to apply flashing around them.

Among all parts of the roof, the skylight is the most sensitive one affected 100 percent by water damage from the raindrops pouring down vertically. Therefore, you should always ensure to seal the skylight flashing before settling down in a new house.

3 Roof Flashing Techniques

1. Step flashing 

This technique is used for the areas where the roof intersects a wall, like a roof dormer protruding out of the roof. When it rains, water drops can flow down the wall, run through the shingles, and go inside the house. 

Step flashing works well in that situation; it directs the water away from the wall to run down into the gutter. It is installed in steps, with layers of shingles between, ensuring that the rain falls on each step and runs along the roof. 

2. Counter flashing

This is often used for chimney flashing. Counter flashing contains 2 pieces of flashing: 

  • Base flashing: this will be wrapped around the bottom of the chimney
  • Counter flashing: this will be embedded into the chimney’s masonry, to prevent water from flowing over the base flashing. 

Counter flashing is the technique of installing a second piece of flashing from the first one. 

3. Plumbing vent boot flashing

Vent flashing has a cylindrical shape to put around the vent. The shingles will be installed over the vent boot so that the boot will have enough height to keep the water run around the vent, not into it. 

Beneficial Roof Flashing Tips

  • Every time you clean the gutters, remember to examine the current state of roof flashing and shingles.
  • If there is any loose nail that weakens the seals of flashing, fasten it and cover the exposed nail heads with roofing cement. 
  • To replace the flashing seal, chip off the old caulking and mortar along the flashing edges. Then recaulk the space between the roof and the current flashing. 
  • After a period of use, corroded flashing needs to be renewed. Remove the old flashing and all shingle rows. Next, put the new flashing on, fasten it, and install the shingles according to the right overlapping procedure.


1. How much does it cost to replace roof flashing?

The price for roof flashing repair usually ranges from $200 to $500 for skylights, chimneys, and vents. Completely replacing the flashing costs $400 to $1,000, which includes sealing and replacing the surrounding shingles.

2. How to Repair Roof Flashing

  • Step 1: Gently pry up the shingles surrounding the damaged flashing. As for step flashing, you also need to remove undamaged pieces of flashing.
  • Step 2: Softly remove the remaining asphalt cement with a chisel.
  • Step 3: If you find leaks or any damage in the underlying roof part, get it repaired completely.
  • Step 4: Reinstall the new flashing and shingles, using the techniques mentioned above.

You can check out this video for a full tutorial:

3. When do you need to repair roof flashing? 

These are the signs showing that it’s time to repair your roof flashing:

  • Damage, holes, or bending.
  • Corroded or rusty areas.
  • Loose or missing nails.
  • Dried out or missing sealant.
  • Flashing becoming loose.
what is roof flashing