Flashing Methods Have Changed Since Your Chimney First Met the Roof

The Seam That Was Never Meant to Last as Long as the Chimney

A masonry chimney can stand for the better part of a century with the right maintenance, but the flashing sealing it to the roof around it was rarely built with that same lifespan in mind. Flashing is metal, thinner and more exposed than the brick it protects, and the materials and methods used to install it decades ago were not always chosen with a multi-decade service life as the goal. This piece looks at how flashing practice has changed since a lot of the original chimneys in this part of the valley first met their roofs, and why that gap between an aging chimney and its original flashing is worth understanding.

What Flashing Actually Does

Flashing is the metal barrier installed at the joint where a chimney passes through the roofline, designed to keep water from working its way into the gap between two very different materials, brick and roofing, that expand, contract, and shed water differently from each other. A complete flashing system generally includes step flashing, individual pieces woven into the roofing material along each side of the chimney, and counter flashing, a separate piece set into the mortar joints of the chimney itself and folded down over the step flashing to shed water away from the seam entirely.

How Older Flashing Installations Differed From Current Practice

Flashing materials and installation methods used on homes built decades ago throughout Studio City and Burbank were not always as corrosion resistant or as carefully layered as what current roofing and chimney work calls for. Some original installations relied on a single piece of flashing rather than the separate step and counter flashing approach used today, or used a thinner gauge metal that corrodes faster than more current materials. Sealant was sometimes used in place of proper mechanical flashing at certain joints, a shortcut that works for a while but degrades faster than metal built into the roofline correctly from the start.

Why Roof Replacements Do Not Always Fix Chimney Flashing

Homeowners in Sherman Oaks and Woodland Hills who have had their roof replaced at some point often assume the flashing around the chimney was addressed as part of that project. That is not always the case. A roofing crew focused on the field of the roof may reuse existing chimney flashing rather than replacing it, particularly if the flashing appeared intact at the time and coordinating chimney-specific flashing work was outside the scope of the roofing contract. This means a chimney can end up with a newer roof surrounding decades-old flashing that was never actually addressed, a mismatch that is easy to miss unless someone specifically checks the chimney joint rather than the roof as a whole.

Where Original Flashing Tends to Fail First

Counter flashing set into the mortar joints of the chimney is often the first point of failure on an original system, since the mortar around it ages and can crack or crumble, loosening the metal's anchor point even if the flashing itself is still structurally sound. Step flashing along the sides of the chimney can corrode at the point where each piece overlaps the next, particularly on a chimney that has stood through decades of valley heat cycling. The cricket, a small peaked structure built behind a wide chimney to divert water around rather than letting it pool against the uphill side, is sometimes missing entirely on original construction from an era when this detail was not always considered standard on every chimney width.

What Water Intrusion at the Flashing Actually Damages

Water that gets past failing flashing does not stay at the roofline. It works down into the attic space around the chimney chase, can reach the wood framing surrounding a masonry structure, and eventually finds its way into the mortar joints of the chimney itself from the outside, compounding whatever aging is already happening to that mortar from decades of weather exposure. Staining on an attic ceiling near the chimney, or water spots on an interior wall close to where the chimney passes through the house, are both signs that flashing deserves a look well before the damage becomes visible from outside.

Assessing Original Flashing on an Older Chimney

Checking flashing condition means examining the counter flashing anchor points in the mortar for looseness or cracking, inspecting step flashing along both sides of the chimney for corrosion or gaps at the overlaps, and confirming a cricket is present and functioning correctly on any chimney wide enough to need one. On chimneys throughout Burbank near the Verdugo Mountains and hillside properties in Woodland Hills, we also check how flashing has held up against the wind-driven rain that comes with storms moving through this terrain, since exposure varies more on these properties than on a flat, sheltered lot.

Repairing Versus Fully Replacing Flashing

Flashing repair on an older chimney sometimes means resealing or resetting counter flashing that has come loose from crumbling mortar without disturbing sound step flashing elsewhere. In cases where corrosion has progressed further, a full flashing replacement, done to current step and counter flashing standards rather than whatever shortcut method the original installation used, gives the chimney a properly layered seal built to modern expectations rather than repeating whatever compromise went into the original work decades ago.

How Valley Storms Test Flashing Differently Than Steady Rain

Rainfall throughout this part of the valley tends to arrive in shorter, more intense storm systems rather than steady, gentle rain spread evenly across many days, and wind-driven rain during those storms can push water sideways into a flashing seam that would otherwise shed a straight downpour without issue. Hillside properties throughout Woodland Hills and Sherman Oaks, along with taller original chimneys common in Studio City, see more of this wind-driven exposure than a sheltered, single-story lot would, which is part of why flashing that has held up for years without an obvious problem can still fail during one particularly wind-heavy storm system. Checking flashing before the rainy season begins, rather than after a leak has already shown up on an interior ceiling, gives time to address a weak seam before it gets tested by the kind of storm that actually finds the gap.

Coordinating Flashing Work With Other Chimney Repairs

Flashing problems often surface alongside other original construction issues, since a chimney old enough to have never received a proper step and counter flashing system is frequently the same chimney showing crown cracking or mortar joint wear from the same decades of exposure. When we find flashing that needs attention, we typically check crown condition and the surrounding masonry at the same visit, since addressing flashing without also confirming the crown is sound can mean paying for a new seal around a chimney that is still letting water in from a different point entirely. Bundling this assessment into one visit, rather than treating flashing as a separate project from the rest of the chimney's condition, gives a more complete picture of where a decades-old system actually stands.

Getting Your Chimney's Flashing Checked

If your chimney's flashing has never been assessed on its own, separate from a roof replacement or general roof inspection, it is worth having someone look specifically at that joint before the next rainy season arrives.

Contact Blackstone Chimney Sweep at (820) 345-0340 to schedule a flashing assessment. Homeowners in Studio City, Sherman Oaks, Encino, Woodland Hills, Burbank, and Simi Valley can count on us to coordinate with roofing contractors whenever a project calls for it.