What Is Roof Flashing and Why Do Columbus Roofs Leak There?

What Flashing Is and Why Joints Leak

Shingles shed water by overlapping, each course covering the one below. That works beautifully across an uninterrupted slope. It stops working the moment the water reaches an obstacle, because now the water has to be steered rather than simply dropped downhill.

Flashing is bent sheet metal, usually aluminum, galvanized steel or copper, shaped to carry water around that obstacle and back onto the shingle surface below it. Every joint on your roof has a piece of metal doing that job, and when a roof leaks, the odds strongly favor one of them having failed rather than the shingles themselves.

The Types You Actually Have

You do not need to be able to install these, but knowing the names makes any conversation with a roofer far more productive.

• Step flashing sits where a roof slope meets a vertical wall, for example along a dormer. It is not one long strip. It is a series of small L shaped pieces, one woven in with every single shingle course, stepping up the wall. Long continuous metal in this location is a defect, not a shortcut.
• Counter flashing is the second layer that covers the top of step flashing, usually let into a mortar joint on a chimney so water cannot get behind it.
• Valley flashing runs down the trough where two roof planes meet. Valleys carry more water than anywhere else on the roof, so this is a high stress detail.
• Vent pipe boots are the collars around plumbing stacks. The metal base is usually fine. The rubber gasket around the pipe is the single most common leak source on an otherwise healthy roof.
• Kick out flashing is a small angled piece where a roof edge meets a wall that continues past it. It kicks water away from the wall and into the gutter. It is frequently missing entirely.

The Two Failures We Find Most Often

The first is a cracked vent boot. The rubber collar around a plumbing stack sits in full sun and full weather, and rubber in Ohio has a hard life. It hardens, splits around the pipe, and drips directly into the attic. It is a genuinely cheap repair and it accounts for a startling share of the leaks we are called out to. If a ceiling stain sits below and slightly downslope of a plumbing vent, look there first.

The second is a missing kick out. Where a roof edge dies into a wall, water that is not kicked clear runs down inside the wall cladding instead. Nothing appears on the ceiling, so nobody notices, and the damage accumulates inside the wall for years before it shows up as rot or interior staining well away from the roof. This is one of the reasons a stain can appear with no visible leak when it rains.

Reused Flashing on a New Roof

This is the one to watch for, and it is the reason to read a roofing proposal carefully.

Flashing is labor. Removing old metal, cutting new pieces, weaving step flashing in course by course and cutting a fresh reglet into a chimney all take time. Shingles are the fast part. On a bid squeezed to win on price, the tempting move is to lay new shingles over the existing flashing and seal the edges with roof cement.

That roof looks brand new from the driveway and has twenty year old metal doing the hardest job on it. The sealant hides it for a season or two, then fails, and now the leak is under a new roof that is technically still in warranty for the shingles. Nobody wants that conversation. This is the same quiet substitution we describe in the questions to ask a roofing contractor, where the parts that get cut are always the ones invisible from the ground.

How to Check Yours from the Ground

Binoculars or a phone camera at full zoom will tell you a surprising amount without anyone getting on a ladder.

At the chimney, look for a clean metal line let into the brickwork rather than a thick smear of black tar. Tar is a repair, not a detail, and it is a sign the joint has already given trouble. Around plumbing vents, look for a collar that still sits tight to the pipe, with no gap and no visible splitting. In the valleys, look for metal that runs straight and clean without debris packed into it. Where a roof edge meets a wall, look for that small kicked out piece at the bottom. If the wall below that point is stained or the siding is discolored in a vertical band, you have found something.

What to Ask For in a Proposal

Ask that the proposal say all flashing is new, not reused. Ask specifically that step flashing be replaced and woven course by course rather than run as continuous metal. Ask that chimney counter flashing be cut into the mortar rather than surface sealed. Ask that vent boots be replaced as part of the job, since they are inexpensive and it is absurd to put new shingles around old rubber. And ask whether kick out flashing is included where roof edges meet walls.

Those five answers tell you more about a roofing company than any brochure will. The edge details follow the same logic, which is why drip edge on a Columbus roof is worth confirming in the same conversation.