The Critical Component Most Contractors Get Wrong

Ask any experienced roofer where leaks occur, and they'll tell you the same thing: flashing. Not shingles. Not underlayment. Flashing.

Flashing is the metal (or occasionally rubber) material installed at roof transitions, penetrations, and intersections to direct water away from vulnerable areas. When flashing fails, water finds its way into your home — often causing thousands of dollars in damage before you even notice the leak.

After 8+ years and hundreds of tear-offs, we've seen it all: missing flashing, improperly installed flashing, corroded flashing, and flashing that was never sealed. This guide explains what flashing is, where it's needed, and how to ensure it's done right.

What Is Flashing?

Flashing is a thin barrier (typically metal) installed at roof intersections and penetrations to prevent water intrusion. It works by:

• Directing Water: Channels water away from vulnerable seams
• Creating Overlaps: Layers flashing to ensure water flows downward, not under materials
• Sealing Penetrations: Wraps around chimneys, vents, skylights to prevent water entry
• Protecting Transitions: Covers areas where roof meets walls, valleys, or other roof planes

The Golden Rule of Flashing: Water must always flow OVER flashing, never under it. Every flashing installation is designed around this principle.

Types of Flashing and Where They're Used

1. Drip Edge (Eave and Rake Flashing)

What It Is:

L-shaped metal installed along roof edges (eaves and rakes) to direct water into gutters and prevent water from wicking back under shingles.

Installation:

• Installed OVER underlayment at rakes (sides)
• Installed UNDER underlayment at eaves (bottom)
• Extends 2-3 inches onto roof deck and 2 inches down fascia

Materials:

• Galvanized Steel: Standard, affordable, 20-30 year lifespan
• Aluminum: Corrosion-proof, lightweight, 30-40 year lifespan
• Painted Steel: Color-matched to shingles or fascia

Why It Matters:

Without drip edge, water runs down fascia boards, causing rot. In Fraser Valley's wet climate, fascia rot is common on older homes without proper drip edge.

2. Step Flashing (Sidewall Flashing)

What It Is:

Individual L-shaped pieces installed where a roof meets a vertical wall (dormers, chimneys, sidewalls). Each piece "steps" up the roof, overlapping the piece below.

Installation:

• One piece of step flashing per shingle course
• Each piece overlaps the one below by 2-3 inches
• Vertical leg extends 4-5 inches up the wall
• Horizontal leg extends 4-5 inches onto roof
• Wall siding overlaps the vertical leg

Common Mistakes:

• Continuous Flashing: Using one long piece instead of individual steps (fails when building shifts)
• Caulk-Only: Relying on caulk instead of proper step flashing (caulk fails in 3-5 years)
• No Counter Flashing: Not extending flashing under siding (water runs behind flashing)

Real-World Example:

We tore off a 10-year-old roof in Mission where the previous contractor used continuous flashing (one long piece) instead of step flashing. The building had settled slightly, creating a gap. Water poured into the wall cavity, causing $8,000 in rot and mold damage.

3. Valley Flashing

What It Is:

Metal installed in roof valleys (where two roof planes meet) to channel water runoff. Valleys handle high water volume and are critical failure points.

Installation Methods:

Open Valley (Our Preferred Method):

• Metal flashing visible in valley center
• Shingles cut back 2-3 inches from valley center
• Water flows freely down metal surface
• Advantages: Superior water flow, easier to clean, longer lifespan

Closed Valley (Woven or Cut):

• Shingles cover valley flashing completely
• Shingles from both roof planes overlap in valley
• Advantages: Cleaner appearance
• Disadvantages: Debris accumulation, harder to inspect, shorter lifespan

Materials:

• Galvanized Steel: Standard, 24-26 gauge
• Aluminum: Corrosion-proof, easier to form
• Copper: Premium, 50+ year lifespan (heritage buildings)

Why It Matters:

Valleys handle 2-4x the water volume of flat roof sections. In Fraser Valley's heavy rainfall, valley flashing failure is a common leak source.

4. Chimney Flashing (Base, Step, Counter, and Cricket)

What It Is:

Multi-component flashing system around chimneys. This is the most complex flashing installation on a roof.

Components:

Base Flashing:

• L-shaped piece at chimney base (downslope side)
• Extends onto roof and up chimney face

Step Flashing:

• Individual pieces along chimney sides
• Same principle as sidewall step flashing

Counter Flashing:

• Embedded into chimney mortar joints
• Overlaps step flashing to prevent water entry

Cricket (Saddle):

• Small peaked structure on upslope side of chimney
• Diverts water around chimney
• Required for chimneys wider than 30 inches

Common Mistakes:

• No Counter Flashing: Water runs behind step flashing
• Caulk Instead of Counter Flashing: Temporary fix that fails in 3-5 years
• No Cricket: Water and debris accumulate behind chimney
• Improper Overlap: Counter flashing doesn't overlap step flashing enough

5. Plumbing Vent Flashing (Pipe Boots)

What It Is:

Rubber or metal collar that seals around plumbing vent pipes penetrating the roof.

Materials:

Rubber Boots (Standard):

• Lifespan: 10-15 years in Fraser Valley (UV and thermal cycling degrade rubber)
• Cost: $15-25 per boot
• Failure Mode: Rubber cracks, allowing water to leak around pipe

Lead Boots (Premium):

• Lifespan: 50+ years
• Cost: $75-150 per boot
• Advantages: Malleable, conforms to pipe, doesn't degrade

All-Metal Boots:

• Lifespan: 30-40 years
• Cost: $40-60 per boot
• Advantages: No rubber to degrade

Our Recommendation:

Standard rubber boots are adequate for most homes, but they're the first thing to fail on a roof. If you're installing a 30-year roof, consider upgrading to all-metal or lead boots ($200-400 total for a typical home) so you don't need to replace boots in 15 years.

6. Skylight Flashing

What It Is:

Pre-fabricated flashing kit (usually provided by skylight manufacturer) or custom-fabricated flashing around skylights.

Installation:

• Base flashing at bottom
• Step flashing on sides
• Head flashing at top
• Ice & water shield around entire skylight opening

Critical Rule: Always use manufacturer-provided flashing kits. Generic flashing voids skylight warranties and increases leak risk.

Flashing Materials: What We Use and Why

Galvanized Steel (Our Standard)

• Thickness: 24-26 gauge
• Coating: G-90 zinc coating
• Lifespan: 25-35 years in Fraser Valley
• Cost: $$ (affordable)
• Best For: Standard residential applications

Aluminum

• Advantages: Corrosion-proof, lightweight, easy to form
• Lifespan: 30-40 years
• Cost: $$$ (20-30% more than galvanized)
• Best For: Coastal areas, high-moisture environments

Copper

• Advantages: 50-100 year lifespan, beautiful patina, prestige
• Cost: $$$$ (5-10x galvanized steel)
• Best For: Heritage buildings, luxury homes, chimneys

Why Flashing Fails

1. Improper Installation (80% of Failures)

Most flashing failures aren't material failures — they're installation failures:

• Incorrect overlap sequences
• Missing components (no counter flashing, no cricket)
• Relying on caulk instead of proper flashing
• Not embedding counter flashing in mortar
• Inadequate overlap (water flows under flashing)

2. Corrosion (15% of Failures)

Galvanized steel eventually rusts, especially in:

• Valleys (constant water flow)
• Areas with moss/debris accumulation
• Coastal environments (salt air)

3. Thermal Cycling (5% of Failures)

Metal expands and contracts with temperature. Improperly fastened flashing can pull away from seals.

The Bottom Line

Flashing is where roofs fail. Not shingles. Not underlayment. Flashing.

When you hire a roofer, pay attention to how they talk about flashing. If they don't mention step flashing, counter flashing, or crickets, they don't understand roofing. If they say "we'll just caulk it," run.

At RJ Roofing Bros, flashing isn't an afterthought. It's the foundation of a leak-free roof.

Concerned about flashing on your roof? Call (604) 997-1292 for a free inspection.