Overview

Roof leaks are disruptive and often hazardous. They damage property and create expensive problems. Is there a reliable defense, or a way to build/maintain your roof that minimizes risk?

This blog answers those questions, spotlighting roof flashing and the critical role it plays in leak prevention and waterproofing. As a roofing company that built its reputation on a deep understanding of water problems, Burrard Roofing & Drainage Inc brings decades of industry insights to the guide below.

Introduction

Sloped roofs require flashing. Pitched roofs require flashing. Asphalt, metal, slate, cedar shakes, and other materials need it, too. You don’t think about it, but it’s always there.

Flashing is such a universally important component, and yet many property owners never know it exists until something fails. However, learning more about how it works and why roofers install it can go a long way toward helping you understand your system and recognizing potential problems early.

What Is Roof Flashing?

Every roof has weak points. The difference between a roof that stays dry and one that develops leaks often comes down to how those vulnerable areas are protected. Enter roof flashing.

Flashing is a thin layer of metal installed anywhere material alone can’t keep water out. Roofs aren't made from one continuous surface. Where flow is interrupted, openings are created where rain could work its way beneath the roof covering. Flashing bridges these transitions.

Roofing systems are designed to manage water, not stop it entirely. Flashing, then, forms part of a layered system that guides moisture away from those areas, letting gravity do the work. Both installation and maintenance are part of keeping this function reliable.

How Is Roof Flashing Installed?

Roof flashing is installed as the roof is built. Once the roof deck and underlayment have been prepared, roofers position flashing in many critical areas (listed further down). Depending on the location, the flashing may be fastened directly to the roof deck, integrated into masonry, or fitted around roof penetrations before the surrounding roofing materials are added.

To ensure the component remains effective, roofers also must:

Overlap each piece of flashing so water continues flowing downhill
Conceal fasteners beneath shingles or the next layer of flashing whenever possible
Bend flashing to match the shape and angle of the roof feature
Seal joints and penetrations where additional waterproofing is required
Leave room for normal expansion and contraction

How Roof Leaks Happen With Compromised Flashing

Let's say a small gap forms in the step flashing at the joint where a roof meets an exterior wall. The opening may be only a fraction of an inch wide, but every rainfall sends water toward that joint. Instead of staying on the roof's surface, some of that water slips through the gap.

Once water passes the flashing, it reaches parts of the roof that were never meant to get wet. It soaks the roof deck, dampens the underlayment, and eventually works its way into the attic or wall cavity. The leak may not become visible indoors right away. Moisture often travels along framing members before staining a ceiling or damaging insulation. Meanwhile, wood rot and mold develop.

This is just one example. There are many potential pathways for water, with the exact sequence and risk depending on which part of the system is compromised.

What’s the Role of Roofing Material in Waterproofing?

You may wonder why flashing is necessary when you already have layers of roofing material doing their job. Whether it’s shingles, metal, cedar shakes, or anything else, the material isn’t idle in this process. It’s actually the first line of defense against water. When rain touches down, the material sheds water, meaning it carries moisture down the roof’s slope and into the gutters.

This is why roofers stress regular maintenance. It’s common for shingles to shift slightly or fall out of place from impact or gradual wear. When this happens, your system loses part of the barrier that directs water safety off the roof, making leaks more likely to happen.

Why Are Roof Joints More Vulnerable to Leaks?

Roof joints are the places where one section of the roof meets another or where the roof connects to a different part of the building. Every joint introduces additional seams, edges, or changes in direction.

In fact, when you call a roofer suspecting a leak, the roof joints are often checked first. Rainwater naturally collects or redirects at these locations, placing greater demands on the roofing system. A broad section of shingles simply guides water downhill, as discussed, but a joint adds complexity, creating more opportunities for water to find an opening.

That’s not to say that leaks aren’t possible in other locations. In those cases, however, there’s usually damage to the roof material itself that’s often hard to miss.

What Areas of a Roof Require Flashing?

We’ve explained how flashing is installed and the nature of how it works, but we haven’t looked closely at the specific parts of the roof where it does its job. Flashing only goes where it’s needed. It would be unnecessary (and impractical) to cover your entire roof with it.

So, where exactly does it go?

Roof Chimneys

Chimneys are one of the largest structures that extend through a roof, making them one of the most demanding areas to waterproof. Unlike a plumbing vent or small roof penetration, a chimney has four sides, each exposed to flowing rainwater from a different direction. This requires several pieces of flashing working together instead of a single section.

Roofers typically install base flashing along the front of the chimney, step flashing up both sides, and a back pan, sometimes called saddle flashing, behind the chimney to divert water around it. A second layer, known as counter flashing, is secured into the chimney's mortar joints and overlaps the flashing attached to the roof. This is standard, but since systems do vary, so can the setup.

Skylights

Not every roof has a skylight, but any roof that does needs careful flashing around it. A skylight creates a framed opening in the roof surface, which means rainwater must be guided around the unit instead of being allowed to collect along its edges. Since skylights sit directly in the path of runoff, even a small installation flaw can create a stubborn leak.

Skylight flashing usually includes a bottom apron, step flashing along the sides, and head flashing at the top. Many skylights also come with manufacturer-specific flashing kits designed to match the unit’s size and roofing material. These pieces move water around the skylight frame and back onto the surrounding roof without relying on exposed sealant as the main defense.

Roof Valleys

Roof valleys are the channels formed where two sloping sections of a roof meet. Instead of directing rainwater toward different edges of the roof, both slopes drain into the same narrow path, concentrating a large volume of runoff in one location. For this reason, valleys handle far more water than most other parts of the roof and require additional protection.

The flashing here must:

Run continuously from the ridge to the eave
Extend beneath the roofing material on both slopes
Remain centered within the valley channel
Keep exposed fasteners out of the main water path

Dormers

Dormers are roofed structures that project outward from a sloped roof, usually to create additional interior space or accommodate a window. Their design introduces several new roof joints.

Each side of a dormer requires step flashing where the walls connect to the roof, while the front and rear transitions use additional flashing to direct runoff around the structure. Since water flowing down the main roof is forced to split and travel around the dormer, these intersections must be carefully layered so that it rejoins the roof surface without reaching the framing beneath.

Plumbing Vents

Plumbing vents are vertical pipes that extend through the roof to release sewer gases and regulate air pressure within a building's plumbing system.

Roofing materials are designed to cover flat surfaces, not wrap around pipes. To address that, roofers install a vent flashing, often called a pipe boot, over each penetration. The base of the flashing slides beneath the surrounding roofing material, while a flexible collar fits snugly around the pipe.

Roof-to-Wall Intersections

Roof-to-wall intersections occur where a sloped roof meets the side of a vertical wall. These connections are common on garages, home additions, second-story walls, and other sections where the roof terminates against the building instead of continuing to the eaves. Since rainwater is directed straight toward the wall, this joint requires careful waterproofing.

Step flashing is installed one piece at a time alongside each course of roofing material. This creates a series of overlapping connections that carry water effectively down the roof.

When Do You Need Roof Flashing Repair?

Flashing can last decades, sometimes through multiple roofs if it's in good condition. However, there are indications that you need a roof flashing repair, regardless of the system’s age.

Some of the most common ones include:

Rust or corrosion on exposed flashing
Bent, lifted, or loose flashing sections
Gaps between the flashing and surrounding roofing materials
Cracked or deteriorated sealant around flashing
Water leaks or interior water stains near chimneys, skylights, vents, or walls

Keep Your Roofing System Watertight

At Burrard Roofing & Drainage Inc, we’ve got your roofing system covered. Our expertise covers all things waterproofing, from the flashing to perimeter drainage and the building envelope. You can trust us to identify the source of leaks, perform lasting repairs, and protect your property from future water intrusion.

Call (604) 986-1812 with your flashing questions or leak concerns!