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Why Roof Flashing Matters
Ask roofers where most leaks start and you'll hear one word: flashing. These unglamorous metal transitions — at chimneys, walls, valleys, skylights, and vents — are the most failure-prone part of any roof. Here's why roof flashing matters more than the shingles around it.
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What flashing does
Every place the roof surface is interrupted — a chimney rises through it, a wall meets it, two slopes form a valley, a pipe pokes out — is a gap water wants to enter. Flashing is the shaped metal that bridges those gaps, directing water back onto the shingle surface and away from the structure. Shingles shed water; flashing manages it at the vulnerable points. When flashing fails, it doesn't matter how good the shingles are.
The main types
- Step flashing — L-shaped pieces woven with each shingle course where roof meets wall; the most common leak point on the planet.
- Counter flashing — the upper piece (often set into chimney mortar) that overlaps step flashing.
- Valley flashing — metal lining roof valleys, handling the heaviest water concentration.
- Drip edge — metal at the eaves and rakes directing water into gutters instead of behind them.
- Pipe boots — rubber or metal collars sealing plumbing vents; the rubber versions crack with UV and age.
How flashing fails
Corrosion, freeze-thaw working joints loose, dried-out sealant, hail denting, and — the classic — being reused during a re-roof when it should have been replaced. In Colorado, the daily temperature swings are especially hard on flashing joints, as metal and surrounding materials expand at different rates. A roof replacement that reuses old flashing is a new roof with old leaks waiting to happen.
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FAQs
How do I know my flashing is failing?
Rust stains, lifted or separated metal, dried and cracked sealant, and — the big one — leaks near chimneys, walls, or valleys. A roofer spots it in minutes during an inspection.
Should flashing be replaced with a new roof?
Yes — always. Reusing flashing is one of the most common installation corner-cuts, and it voids the logic of a new roof. Specify replacement in your estimate.
Related reading
- What Causes Roof Leaks After Heavy Rain? — flashing as leak source #1
- Common Roof Installation Mistakes to Understand — reused flashing and other sins
- What Happens During a Professional Roof Inspection — what inspectors check
- All roofing guides — browse the resource library
Leak near a chimney or wall? It's probably flashing.
One call connects you with an independent roofer who fixes flashing right — no forms, no waiting.
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