Ever wonder what keeps water from leaking around your chimney? Or how rain doesn't pour in where your roof meets a wall? That's roof flashing doing its job.

Roof flashing is thin metal strips installed at joints and edges on your roof to prevent water leaks. It's basically the unsung hero that keeps your house dry—and when it fails, you've got problems.

Why Roof Flashing Matters

Here's the thing: shingles keep most water out, but they can't seal every spot. Anywhere two surfaces meet—your chimney and roof, a wall and roof, a valley where two roof sections join—water tries to sneak in.

Roof flashing creates a waterproof barrier at these vulnerable spots. Without proper flashing, water gets under your shingles, rots your roof deck, damages your attic, and eventually ruins your ceilings.

Most roof leaks happen at flashing, not shingles. That's how important it is.

Where You'll Find Roof Flashing

Chimney flashing. Seals where your chimney pokes through the roof. This is the most common leak spot if flashing fails.

Valley flashing. Where two roof slopes meet and form a V. Water runs fast here, so flashing has to handle heavy flow.

Vent pipe flashing. Around plumbing vents that stick through your roof. Usually has a rubber boot seal.

Skylight flashing. Around all four sides of skylights. Multiple pieces working together.

Dormer flashing. Where dormers meet the main roof. Needs step flashing on the sides.

Wall flashing. Where your roof meets a vertical wall, like on additions or second stories.

Drip edge. Runs along roof edges to direct water into gutters. Technically flashing too.

Types of Roof Flashing

Step flashing. L-shaped pieces that layer with shingles along walls and dormers. Water hits one piece, runs down to the next. Multiple pieces working as a system.

Continuous flashing (apron flashing). One long piece, usually at the base of walls. Works with step flashing above it.

Counter flashing. Goes over base flashing at chimneys. Creates a two-layer waterproof system.

Valley flashing. Long metal sheets in roof valleys. Can be open (metal visible) or closed (shingles cover it).

Drip edge flashing. Metal strips along roof edges. Keeps water off your fascia boards.

Vent pipe flashing. Metal base with rubber boot that seals around the pipe. The rubber wears out over time.

What Roof Flashing is Made Of

Aluminum flashing. Lightweight, rust-proof, affordable. Most common for roof flashing. Works great in Maryland's humid climate.

Galvanized steel flashing. Stronger than aluminum but can rust over time. Needs paint or coating near coastal areas.

Copper flashing. Expensive but lasts forever. Turns green over time (patina). Common on historic homes.

Lead flashing. Old-school material, very durable. Not used much anymore due to cost and health concerns.

Rubber flashing. Used for vent pipes. The rubber boot seals around pipes but degrades in sun after 15-20 years.

In Maryland, aluminum roof flashing is the go-to for most applications. It handles our weather, doesn't rust, and lasts as long as your roof.

How Roof Flashing Works

Roof flashing directs water away from vulnerable spots and onto shingles where it can drain properly.

Think of it like gutters for your roof's joints. Water hits the flashing, runs down its surface, and ends up on shingles below where gravity takes it off your roof.

Good roof flashing overlaps in the right direction—upper pieces lay over lower pieces so water can't run backward under it. It's installed in layers with your shingles so everything works together.

Signs Your Roof Flashing is Failing

Water stains on ceilings near chimneys or walls. Classic sign of flashing failure.

Rust or corrosion on metal flashing. Means it's breaking down and needs replacement.

Gaps or separations. Flashing pulled away from chimneys or walls. Wind and temperature changes cause this.

Cracked or dried rubber boots. On vent pipes, the rubber cracks and splits after years of sun exposure.

Missing pieces. Sometimes flashing just blows off in storms.

Leaks during heavy rain. If you only leak in downpours, it's often flashing related.

Roof flashing problems usually show up 15-20 years into your roof's life. The flashing ages along with shingles, and eventually needs attention.

Can You Replace Roof Flashing?

Yes, but it's tricky. Replacing roof flashing usually means removing shingles around it, installing new flashing, then reinstalling or replacing those shingles.

Chimney flashing replacement is the most common repair. Costs $400-$1,000 in Maryland depending on chimney size.

Valley flashing replacement is more involved because you're removing lots of shingles on both slopes. Runs $500-$1,500.

Vent pipe flashing is easiest—often just replacing the rubber boot. DIY-able if you're handy. Professional repair runs $150-$300.

Most flashing gets replaced when you replace your whole roof. That's the ideal time since everything's exposed anyway.

Roof Flashing Installation

Installing roof flashing correctly is critical. Here's what proper installation looks like:

Overlap properly. Upper flashing always lays over lower flashing. Water can't run uphill.

Seal with roofing cement. All seams and edges get sealed. Not caulk—actual roofing cement that stays flexible.

Integrate with shingles. Flashing goes under shingles above it, over shingles below it. Layered system.

Secure without over-nailing. Too many nails create more leak points. Just enough to hold it.

Use right materials. Aluminum flashing with aluminum nails, copper with copper. Mixing metals causes corrosion.

Bad roof flashing installation is one of the top causes of roof leaks. Cutting corners here costs you big later.

Roof Flashing Maintenance

Roof flashing needs occasional attention:

Annual inspections. Check flashing for rust, gaps, or damage every year.

Re-seal if needed. Old roofing cement cracks. Re-seal gaps before they leak.

Replace rubber boots. Vent pipe boots wear out. Replace them every 15-20 years.

Keep it clean. Remove leaves and debris that trap moisture against flashing.

Fix problems fast. Small flashing issues become big leaks quickly.

Good maintenance makes roof flashing last as long as your roof—25-30 years for most materials.

Roof Flashing Cost

Chimney flashing repair: $400-$1,000
Valley flashing repair: $500-$1,500
Vent pipe flashing: $150-$300
Step flashing replacement: $300-$800
Full roof flashing (new roof): Included in roof replacement cost

Flashing is usually 5-10% of your total roof replacement cost. Cheap out on flashing and you'll pay for it in leaks.

Why Roof Flashing Fails in Maryland

Maryland weather is tough on roof flashing:

Temperature swings expand and contract metal, creating gaps over time.

Ice dams in winter force water under flashing at roof edges.

Humidity accelerates rust on steel flashing near the Chesapeake Bay.

Storms physically damage flashing with wind and hail.

UV exposure degrades rubber boots on vent pipes.

This is why quality flashing materials and proper installation matter in Maryland. Cheap flashing fails faster in our climate.

Bottom Line: What is Roof Flashing

Roof flashing is thin metal that seals joints on your roof to prevent leaks. It goes around chimneys, in valleys, along walls, and around anything that penetrates your roof.

Without good roof flashing, even the best shingles can't keep your house dry. Most roof leaks trace back to failed or improperly installed flashing.

When you get a roof replacement, pay attention to the flashing. Good contractors use quality materials and install it right. Bad contractors cut corners here—and you pay the price in leaks.

Got roof flashing problems or leak around your chimney? Visit bvexterior.com or call us for a free inspection. We'll check your flashing, find any issues, and fix them right. Serving Maryland homeowners with honest roofing solutions.

Because good flashing is the difference between a dry house and a wet nightmare.