Roof Flashing Problems:
What Home Buyers Need to Know

What Roof Flashing Actually Does

Anywhere two surfaces meet on a roof, there’s a gap. Shingles can’t seal those gaps on their own. They’re designed to shed water across a flat plane, not around a corner or into a joint. Flashing bridges those transitions and redirects water away from the building.

The most common locations are chimneys, where the masonry meets the roof deck from four sides. Wall-to-roof transitions, where a sloped roof meets a vertical wall. Valleys, where two roof planes come together. Skylights. Pipe penetrations. Every one of these is a potential entry point if the flashing fails.

Good flashing is installed in layers. Step flashing, for example, is a series of individual L-shaped metal pieces woven into the shingles one course at a time as the roof is built. When it’s done right, water can’t get behind it. When it’s done wrong, or when it’s just old, it doesn’t take long for the Pacific Northwest rain to find the gap.

Where Flashing Fails Most Often

Chimneys are the number one spot. Chimneys move. They expand and contract with temperature, they settle slightly, and they’re exposed to weather on all four sides. Even well-installed chimney flashing has a finite life. When the caulk dries out and the metal separates, water gets in at the base and runs down inside the wall or ceiling below.

There are two parts to chimney flashing: base flashing that steps up along the sides, and counter-flashing that’s cut into the mortar joints and laps over the top of the base flashing. Both need to be present and in good shape. Counter-flashing that’s just caulked to the brick face, rather than embedded in the mortar, is a red flag.

Kickout flashing is small but critical. It’s the piece at the bottom of a roof-to-wall junction that directs water into the gutter instead of behind the siding. It’s also frequently missing, especially on older homes and on additions built before kickout flashing became standard practice. When it’s not there, water runs right down the back of the siding and into the wall. This is one of the leading causes of hidden rot in Pacific Northwest homes.

Roof valleys are high-traffic zones for water. Two roof planes coming together means water from both sides converges in one spot. Valley flashing that’s improperly lapped, corroded, or has open seams can let water under the roof deck. On older homes, open valleys with exposed metal are common, and fine as long as the metal is in good shape. Woven or closed-cut valleys with no metal should be inspected carefully.

Skylights have their own flashing system and their own failure modes. Most skylight leaks aren’t the skylight itself. They’re the flashing around it. Integrated flashing kits from reputable manufacturers hold up well. Field-fabricated flashing or older installations that rely heavily on caulk are less reliable.

Pipe penetrations (plumbing vents, exhaust fans, HVAC) each need a boot or collar flashing sealed around the penetration. Rubber boots crack over time, especially in UV-exposed locations. Neoprene or metal boots last longer. When the seal goes, water gets in right at the pipe.

What an Inspector Looks For

During a roof inspection, Russ gets as close to the roof as safely possible. Trusted Home Inspections includes a walked roof inspection when conditions allow, and a drone inspection when the pitch or surface isn’t safe to walk. Both methods get eyes on the flashing at the major transitions.

What he’s looking at: separation between the flashing and the surface it’s meant to seal. Corrosion that’s compromised the metal. Caulk that’s dried and cracked. Missing pieces, especially kickout flashing at wall junctions. Step flashing that’s been installed incorrectly, or simply replaced with a single continuous piece when individual steps were needed. Signs that a DIY repair was attempted with roofing cement instead of proper flashing.

He’s also looking inside. Staining on rafters, on the underside of the roof deck, or on the ceiling below can tell the story of past or ongoing leaks, even if the source hasn’t been identified from outside. Thermal imaging, included on every inspection, can show temperature differences that may point to moisture in wall assemblies or ceiling cavities.

The post on water stains on the ceiling covers how Russ reads a stain by where it sits, and why a dry reading on inspection day doesn’t mean the leak is fixed.

The report documents what was observed at each location with photos. Where flashing damage or suspect installations are found, the report notes it and may recommend evaluation or repair by a licensed roofing contractor.

Flashing and Portland’s Older Housing Stock

Portland and the surrounding metro have a lot of older homes. Oregon City, Milwaukie, SE Portland, NE Portland, Gresham, and parts of SW Washington all have significant housing stock from the 1940s through 1970s. Homes that age often have original flashing, which means flashing that has been exposed to 50 to 80 years of Pacific Northwest weather.

In that climate, original flashing is usually at or past the end of its useful life. Galvanized steel corrodes. Tar-based sealants dry and crack. Mortar joints that once held counter-flashing in place erode. Additions built by previous owners don’t always have proper flashing at the new roof-to-wall junctions.

That doesn’t mean every older home has a leak. It means the flashing on older homes deserves close attention. And it means buyers of older homes should expect the inspector to spend real time at the chimney, the walls, and the penetrations.

What Happens After the Inspector Flags Flashing

When the report documents a flashing concern, the next step is typically to have a licensed roofing contractor take a closer look. The inspector’s job is to identify and document conditions, not to open up the roof or determine the full extent of any water intrusion that may have occurred.

A roofer can assess whether the flashing can be repaired in place or needs to be replaced, and whether there’s damage to the roof deck or wall sheathing underneath that needs to be addressed at the same time. If there’s any sign of moisture getting inside (staining, soft materials, musty odors), a mold assessment may be worth scheduling as well.

The inspection report gives you the documentation you need to understand what’s there. What happens next is a conversation between you and your agent.

Ready to schedule a buyer’s inspection? See what’s included with every buyer’s home inspection or book online. Thermal imaging is included on every inspection at no extra charge, useful for spotting temperature differences that can point to moisture. Learn more about thermal imaging inspections.