Roof Flashing: What Is It, and How Does It Work? (2024)

Installing roof flashing is critical in preventing roof-related damage to your home. Without it, water can get under your shingles, leading to water damage, potential wood rot, and even structural damage. But what exactly is roof flashing, and what does it do?

In this article, we’ll cover the different types of roof flashing, how to tell when it needs to be replaced, how it’s installed, and more.

What is roof flashing?

Roof flashing is a thin piece of sheet metal typically made from galvanized steel, aluminum, or copper that’s used to direct water runoff away from susceptible areas and seal the roof covering at all edges.

Flashings are usually placed underneath shingles and applied at the points where the roof covering is interrupted, like around chimneys and vents, where the roof deck and walls meet. They are also used at the intersection of different materials, like shingles or felt and metal.

Types of roof flashing

Residential flashings are typically made of a non-corrosive metal applied between an underlayment and a shingle layer to prevent water penetration. There are several types of flashings and installation methods, including the following:

• Base flashing: This is an underlayment material applied directly at the joint of the horizontal roof deck and a vertical feature, such as a wall or skylight box.
• Continuous flashing: Also called “apron flashing,” this type of flashing uses a single piece of metal and is applied at the joint of the roof and the sidewall.
• Step flashing: This type of flashing is a rectangular metal piece bent in a ‘L’ shape at a 90-degree angle. For homeowners, step flashing is usually a more popular choice than continuous flashing, as its design makes it harder for water to travel underneath the surrounding shingles.
• Counter flashing: Counter flashing serves as additional covering applied over base flashing and step or continuous flashing. Metal counter-flashing can be secured directly to a wall or set in a cut-out masonry joint.
• Drip edge flashing: This metal flashing is applied at the roof eaves or edges. It is a continuous metal or plastic piece that covers the transition between the roof deck and the fascia board. The primary purpose is to prevent water, snow, and ice build-up at the roof edge or gutter from backing up into the house.
• Valley flashing: The roof valley is where two roof slopes intersect. This is a point where water can collect, leading to potential leaks. Underlayments or eaves flashing are applied over the roof deck at these points for waterproofing protection.
• Vent pipe flashing: Most manufacturers provide pre-fabricated covers for vent pipes and other types of penetrations. These accessories are made from plastic, metal, or rubber with a base applied over the vent. The materials erode over time and require repairs, typically made with roof adhesives.

Roof flashing materials

As mentioned, many materials can be used for residential steep-slope flashing. A few of the most frequently used materials include:

• Aluminum: Aluminum is a popular material for flashing due to its high durability, low cost, ability to bend, and lightweight qualities. However, it may require a special coating to avoid corrosion if it comes in contact with concrete or any masonry. 
• Galvanized steel: Galvanized steel is a readily available and cost-effective flashing material. The galvanized metal used for flashings should have a special zinc coating (galvalume) that protects it from corrosion. 
• Copper: Copper flashing is incredibly durable, corrosion-resistant, and can be soldered. Copper flashings are typically applied at chimneys and valleys or step flashings on hips and ridges in exposed areas.
• Sealants: Sealants or caulking are required at the joints above metal terminations.
• Additional materials: Adhesives, roof cement, and other roof-grade materials may be used for repairs or flashing installation.

How much does roof flashing cost?

On average, roof flashing costs between $300 and $1,450.

This cost depends on several factors, including the extent of the damage done to your roof flashing, whether it needs a few simple repairs or completely replaced, the size of your roof, and the materials required.

How can you tell when your roof’s flashing needs to be repaired or replaced?

Flashing problems arise over time as the materials wear out or become damaged. So, unfortunately, you likely won’t notice an issue with your roof flashing until it’s fully deteriorating and causing interior water leaks.

Homeowners can avoid roof leaks and extend the service life of flashing materials by getting routine roof inspections. Due to the risks associated with being on a roof and the complexity of the materials, we always recommend hiring a professional roofing contractor to perform any inspections and needed repairs.

Some of the visible signs your inspector will look for that indicate flashings require repair or replacement are as follows:

• Openings, splits, and cracks in the flashing materials
• Openings or missing sealant at flashing terminations
• Decay or staining
• Missing metal flashing materials, such as nails or other metal pieces
• Gutter issues such as rusting, sagging, bending, or having open seams

As a homeowner, you can inspect for further signs of roof leaks in your house using the following procedures:

• Inspect the attic area for water spots, mold, or damaged rafters.
• Inspect the walls for moisture stains, typically shown as brown, yellow, or gray marks.
• Monitor your electric bill for sudden increases in energy costs, which may be associated with openings in your roof. 

How to repair roof flashing

There are multiple techniques for repairing flashings. Some minor damage to flashing materials can be easily repaired by a handy homeowner following these steps:

• Gently lift the existing shingles around the flashing material. Do not damage the shingles in the process, or you may need to replace them.
• Remove the existing flashing by carefully chiseling out the sealant or removing the nails/fasteners.
• Inspect the base flashing for damage once the top metal flashing has been removed.  Complete the proper repairs or remove any damaged base flashing.
• Install new metal flashing following local code requirements.

Again, for more extensive repairs, we recommended hiring a professional roofer. Hiring a contractor will significantly lower the chance of long-term leaks leading to wood rot or structural damage.

Frequently Asked Questions

Is roof flashing necessary?

Yes, roof flashing is necessary. In fact, it is the most critical component of the roof system, as most roof leaks occur at joints, valleys, and other features that flashing covers. Most municipal building codes require roof flashings.

Can you add flashing to an existing roof?

Yes, a professional roofer can install new flashing on existing roofs. New flashing is often added to replace the damaged existing flashing.

Does flashing go under shingles?

Yes, flashings are applied under shingles.

Can you re-use the old roof flashing?

If you’re getting a roof replacement, your existing flashing may be reinstalled if it is in satisfactory working condition. If your roofing company wants to reuse your old flashing material, it will make sure it is not damaged during your roof removal.