Roof Flashing Repair Around Chimneys Walls and Vent Pipes

Most roof leaks aren’t in the middle of a slope. They’re at the joints, where the roof meets a chimney, a wall, a vent pipe or another roof plane.

Flashing is the sheet metal that makes those joints watertight, and it’s the part of a roof that’s most often done badly. TurnKey Roofers finds flashing problems on New Orleans roofs constantly, often on roofs that are otherwise in decent shape.

If you’ve got a stain that keeps coming back in the same spot, use the contact page or call (504) 732-0336 and we’ll trace it.

Key takeaways

• Flashing is thin sheet metal installed where a roof is most likely to leak, including valleys and chimneys.
• Code requires base flashing of corrosion-resistant metal at least 0.019 inch thick, or mineral-surfaced roll weighing at least 77 pounds per 100 square feet.
• A cricket or saddle is required on the ridge side of any chimney or penetration more than 30 inches wide measured across the slope.
• Flashing against a vertical sidewall has to be done by the step-flashing method, one piece per shingle course.
• HomeGuide puts flashing repair at $200 to $500 and full flashing replacement at $400 to $1,000.
• Most roof replacement estimates already include new flashing, so it’s worth checking yours does.

Where flashing goes and what each piece does

Flashing isn’t one product. It’s a family of pieces, each shaped for a particular joint, and a roof usually has several types working together.

• Drip edge. Code treats this as base flashing at the eaves and rakes. It directs water off the deck and gives the starter strip something to bond to.
• Step flashing. Individual L-shaped pieces woven in with each shingle course where a slope meets a vertical sidewall.
• Counter or cap flashing. The upper piece, let into or fastened over a masonry wall or chimney, covering the top edge of the step flashing.
• Apron and head flashing. Used where a slope runs into a vertical front wall or where a wall sits above a roof plane.
• Pipe boots and collars. The flashing around soil stacks and vent pipes, usually metal with a rubber or lead collar.
• Valley lining. The metal or membrane running down the intersection of two roof planes.
• Crickets and saddles. A small peaked structure behind a chimney that splits water around it.

What the code actually specifies

LSU AgCenter’s guide to code-compliant roofing installation sets out the requirements clearly for Louisiana homeowners, drawing on the residential code.

Base flashing, which includes drip edge, has to be corrosion-resistant metal of at least 0.019 inch thickness, or mineral-surfaced roll roofing weighing at least 77 pounds per 100 square feet. Cap flashing carries the same 0.019 inch minimum.

Sidewalls get step flashing specifically. The code language is that flashing against a vertical sidewall shall be by the step-flashing method, which rules out running a single continuous strip up the wall.

Chimneys wider than 30 inches need a cricket. A cricket or saddle is required on the ridge side of any chimney or penetration more than 30 inches wide measured perpendicular to the slope, and the covering has to be sheet metal or the same material as the roof.

Vent pipes and front walls fall back on the manufacturer. Code sends flashing at a vertical front wall, soil stacks, vent pipes and chimneys to the asphalt shingle manufacturer’s printed instructions.

Valleys have their own rules

The metal thickness table in the same guide is specific by material, including aluminium at 0.024 inch, galvanized steel at 0.0179 inch in 26 gauge zinc coated G90, and cold-rolled copper at 0.0216 inch nominal.

LSU AgCenter adds a Gulf Coast note worth following. If you choose galvanized metal for your flashing, hot-dipped is the better choice, and hot-dipped galvanized fasteners last longer in coastal conditions than electroplated ones.

Why flashing fails

1. Reused flashing on a new roof. The cheapest way to cut a re-roof price is to shingle around the old flashing instead of replacing it.
2. Caulk instead of metal. Sealant has a service life measured in a few years. Metal lapped correctly sheds water without depending on it.
3. One continuous strip at a sidewall. A single bent piece up a wall leaves no path for water that gets behind it, which is why code calls for step flashing.
4. No cricket behind a wide chimney. Water and debris collect on the uphill side, the joint stays wet, and the flashing rusts from behind.
5. Perished pipe collars. The rubber collar around a vent pipe hardens and splits long before the shingles are finished.
6. Movement. Masonry and framing move at different rates, which opens the joint between counter flashing and the wall.
7. Fastener corrosion. Mixed metals and the wrong galvanizing fail fast in salt air.

What a repair involves

A proper flashing repair means lifting the shingle courses around the joint, removing the old metal, fitting new pieces in the right sequence and re-laying the shingles over them. It isn’t a caulk-and-walk job.

At a sidewall, that means one step flashing per course, each lapped by the one above. At a chimney, it means step flashing up both sides with counter flashing above, a base or apron piece at the downhill side, and a cricket behind if the chimney is wide enough to need one.

At a vent pipe, the new boot slides under the shingles above and over the shingles below. Our post on vent pipe leaks goes into that detail, and the roof flashing repair page covers how we handle the work.

How to tell a flashing leak from a shingle leak

The location of the stain is the first clue, though water travels along rafters before it drops. A stain that lines up with a chimney chase, a wall above a lower roof or a plumbing vent points at flashing rather than the field of the roof.

Timing is the second clue. Flashing leaks often show up in wind-driven rain rather than in a steady downpour, because the water is being pushed sideways into a joint instead of running over it.

Repetition is the third. A leak that returns in the same spot after a shingle was replaced usually means the water is entering above where anybody looked.

In the attic, follow the wet line uphill with a flashlight. Water will track down the underside of the sheathing and along a rafter, so the entry point is almost always higher than the drip.

What it costs

• HomeGuide puts flashing repair at $200 to $500, with completely replacing the flashing at $400 to $1,000.
• A roof leak repair generally runs $150 to $1,000 or more, and asphalt shingle roof repair $350 to $1,500.
• Most installers include new flashing in a roof replacement estimate, which HomeGuide notes directly.
• A roof inspection to find the source costs $100 to $400.
• Skylight replacement, which often involves the surrounding flashing, runs $800 to $2,400.

Those are national averages and your quote will vary with access, the number of joints and whether the decking underneath has been wet long enough to need replacing.

Doing it yourself, honestly assessed

Flashing work happens at the edges and penetrations, which are the awkward parts of a roof, and it requires lifting sealed shingles without breaking them. That’s harder than it looks, particularly on a hot day when the seal strips are soft.

The safety side is not negotiable. Fall protection is required for work six feet or more above a lower level, and OSHA’s guidance is not to stand on a roof steeper than 4 in 12 without a conventional fall protection system.

A damaged roof adds another layer. OSHA says nobody should work on top of a damaged roof until its strength and structural integrity has been determined.

If the leak is at a pipe collar on a low-slope section you can reach safely, that’s a reasonable homeowner job. A chimney, a sidewall or a valley isn’t.

Frequently asked questions

How can I repair roof flashing myself?

The realistic homeowner job is replacing a split pipe boot on a low, safely reachable slope, sliding the new one under the shingles above and over the ones below. Anything at a chimney, sidewall or valley means lifting sealed shingle courses and rebuilding a lapped sequence, and code requires the step-flashing method at a vertical sidewall rather than a single continuous piece. Before any of it, remember fall protection is required at six feet or more and OSHA says not to stand on a roof steeper than 4 in 12 without a conventional system.

How much does it cost to replace flashing on a roof?

HomeGuide’s figures put flashing repair at $200 to $500 and complete flashing replacement at $400 to $1,000. Cost moves with the number and type of joints involved, since a chimney with a cricket is a much bigger piece of work than an apron at a dormer. HomeGuide also notes that most installers include new flashing in a roof replacement estimate, so on a full re-roof it shouldn’t be a separate line.

What can I do to fix loose flashing on my roof?

Loose counter flashing at a masonry wall usually means the fixing into the mortar joint has failed, and re-bedding it is masonry work as much as roofing. Resist the urge to run a bead of sealant along the top edge, because that hides the problem while the joint keeps moving. Get it looked at, since code sets a minimum 0.019 inch thickness for cap flashing and a piece that has worked loose is often thin, corroded or was never fixed correctly.

Does new flashing come with a new roof

It should, and HomeGuide notes that most installers include new flashing in the estimate. New Orleans reinforces the point in its own process, listing installation of the drip edge and flashing as one of the four stages photographed for a residential re-roofing permit. Ask for it in writing.

Find the leak before it finds the decking

Flashing problems are cheap to fix early and expensive once water has been sitting on the sheathing for a season. If a stain keeps returning in the same place, that’s a flashing conversation.

Call (504) 732-0336 for a free estimate and we’ll trace the leak properly rather than guessing at it.

Related reading

• How to Identify and Fix Common Roof Leaks
• Soffit and Fascia: Why They Matter for Your Roof’s Longevity

Sources

• LSU AgCenter, Consumer’s Guide to Code-Compliant Roofing Installations
• HomeGuide, Roof Replacement Cost (2026)
• OSHA 1926.501, Duty to have fall protection
• OSHA, Roof Tarping (Blue Roof) Safety fact sheet
• City of New Orleans, Residential Re-Roofing Permit
• LSU AgCenter, Roofing to Resist Wind and Rain Damage