Fifteen years hanging plasterboard taught me more about where roofs actually leak than any classroom ever did, because I was the one called back eighteen months later to fix the ceiling stain nobody could explain. It was never the field of the roof. It was always a penetration — a vent pipe, a skylight curb, a chimney chase — where the flashing had been installed as an afterthought instead of as the first thing planned. On one job in particular, a bathroom exhaust vent through a tile roof, the roofer had dressed the tiles neatly around a flashing collar that was never actually sealed to the pipe itself. Looked immaculate from the ground. Leaked for two years before anyone traced the water back to it.
Why Penetrations Fail Before the Roof Field Does
A roof’s main surface is a continuous, engineered water-shedding system. Every penetration — vent, flue, skylight, solar mount, satellite dish bracket — is a deliberate interruption of that system, and the flashing around it is the only thing standing between a clean roof and a slow ceiling stain. Manufacturers typically rate a well-installed flashing assembly to outlast the roofing material around it, but that assumes correct layering: flashing goes under the upslope roofing course and over the downslope one, every time, with no exceptions for awkward angles or tight corners.
Sealant is not a substitute for correct layering. I’ve pulled apart penetrations on Gold Coast homes where a tradesperson relied on a bead of roofing sealant to bridge a flashing gap instead of extending the metal properly, and in a region with genuinely heavy subtropical downpours, that sealant has maybe three to five years before UV and thermal cycling crack it and the leak returns.
What a Failed Flashing Actually Looks Like From the Ground and the Attic
From the ground, look for streaking below any penetration, lifted or cracked sealant beads, and rust staining running down from a metal flashing collar. From inside the attic or roof space, the tell is usually a stain on the sheathing directly beneath the penetration, sometimes with a visible nail or fastener showing daylight around it. On an Adelaide inspection last winter, on a house with a solar hot water system mounted through a corrugated roof, the giveaway wasn’t a stain at all — it was a line of rust bleeding from every screw fixing the mounting bracket, which meant the screws themselves had been driven through without any flashing or sealing washer at all.
Chimney flashing deserves its own mention because it fails differently. Step flashing along the sides of a masonry chimney relies on individual pieces tucked under each course of roofing and the counter-flashing embedded in the mortar joint above. If a previous repointing job disturbed that counter-flashing, or if it was never properly embedded to begin with, water tracks behind it regardless of how good the step flashing below is. On a Texas inspection with a brick chimney through an asphalt roof, this was exactly the sequence — a repointing crew had caulked over disturbed counter-flashing instead of reinstalling it correctly, and caulk over a structural flashing gap buys maybe two summers before it opens back up under thermal movement.
What It Costs to Fix Properly
Re-flashing a single vent penetration correctly, tearing back roofing material and replacing the collar and step flashing, typically runs $250 to $600 depending on roof pitch and material. A chimney counter-flashing repair that requires cutting a new reglet into the mortar joint runs higher, generally $500 to $1,200, because it’s masonry work as much as roofing work. Anyone quoting a fix using sealant alone on a structural flashing failure is offering a temporary patch, not a repair, and it’s worth saying so plainly in the report.
Buyers reading a report that flags multiple flashing issues sometimes assume the whole roof needs replacing. It usually doesn’t — the field of the roof and the flashing details are separate line items with separate remaining service lives, and reading the report section by section instead of jumping to the summary is what keeps that distinction clear. On the broader question of how a jurisdiction defines acceptable moisture control at these details, the Building Code’s external moisture provisions lay out the underlying performance requirement that flashing details exist to satisfy, even outside New Zealand.
Frequently asked questions
Can flashing be inspected without walking the roof? Partially. Binoculars from the ground and photos from a drone or a ladder catch obvious staining and lifted flashing, but confirming correct layering under the roofing material usually requires either a roof walk or an attic inspection during or after rain.
Is a small amount of sealant around a penetration always a red flag? No — sealant used to finish and protect a correctly layered flashing detail is normal and expected. It’s a problem only when the sealant is doing the flashing’s job instead of supplementing it.
How urgent is a flagged flashing issue compared to other roof defects? It depends on the interior evidence. Active staining or soft sheathing beneath the penetration means water is already getting in and it should be addressed before the next significant rain; dry staining with no current moisture reading can usually wait for a scheduled repair.