The call usually starts the same way. There’s a brown ring on the ceiling right beside the chimney breast, it only appears after a blustery southerly, and someone has already been up there with a tube of silicone. Twice. In most of these cases the tiles are fine. The problem is the flashing, and roof flashing repair is one of the most common leak jobs we do on the Mornington Peninsula. It’s also one of the jobs we most often see done badly, so it’s worth knowing what flashing does and why it lets go.
Flashing seals every spot where your roof meets something else
Out in the open, tiles and metal sheets shed water well. Trouble starts at the edges: where the roof runs into a wall, wraps around a chimney, gets cut for a vent pipe or skylight, or meets a second roof at an angle. Flashing is the strip of metal (or flexible flashing material) that bridges those gaps and steers water back out onto the roof instead of into the ceiling.
Most homes have several kinds, and knowing the names helps when a roofer explains what’s wrong:
- Apron flashing: runs along the base of a wall or chimney where it sits on the roof below
- Step flashing: climbs the sides of a chimney or wall in a staircase pattern as the roof slopes
- Counter flashing: tucked into a mortar joint in the brickwork and folded down over the flashing underneath, so water can’t run in behind it
- Back gutter: the small channel on the high side of a chimney that catches water coming down the roof and sends it around
- Penetration flashings: the rubber or metal collars around flues, vent pipes and exhaust fans
Valleys do a similar job but fail for their own reasons, which we’ve covered separately in why roof valleys leak and how they’re fixed.
Why flashings fail on Peninsula homes
Silicone is the first thing we look for, and we usually find it. Sealant gets squeezed into a gap, looks fine for a season, then hardens in the sun and pulls away from the brick or metal. The next owner adds another layer. By the time we arrive there can be three generations of sealant with the original gap still sitting underneath all of it.
On older brick homes, counter flashing working loose is the next most common culprit. That flashing is only as good as the mortar joint holding it. As the mortar crumbles, the flashing lifts, and water that hits the chimney face runs straight down behind it.
Then there’s metal chemistry, which surprises a lot of people. Lead flashings were standard on older tile roofs, but water running off lead or copper onto Zincalume speeds up corrosion of the steel. We regularly see neat rust lines on a metal roof directly below an old lead flashing that was left in place when the roof was resheeted.
Weather plays its part too. In the exposed coastal suburbs, from Rosebud down to Portsea, wind pushes rain sideways and even uphill under laps. A flashing that is too short, or wasn’t turned up properly at the back edge, can cope with straight-down rain for years and then overflow in the first strong blow from the wrong direction. Salt air also eats at cut edges and fixings faster than it does inland.
Renovations round out the list. When an extension is tied into an existing roof, the flashing where old meets new is often the last thing done and the first thing to leak. Rubber pipe collars are similar: they perish and crack in the sun, quietly, where nobody looks.
The clues usually point to flashing before anyone gets on a ladder
Where the stain sits tells you a lot. A water mark in the middle of a ceiling could be many things. A mark hugging the chimney breast, running along the line of an outside wall, or circling a flue or exhaust fan points hard at the flashing above it.
Timing matters as well. If the leak only shows up when the wind comes from one direction, that’s classic flashing behaviour, because water is being driven past a seal that copes fine in calm rain. Damp patches on the inside face of a chimney, bubbling paint on a wall below a roof junction, or a musty smell in one corner of a room deserve attention for the same reason. If your leak only appears in a real downpour, our guide to roofs that only leak in heavy rain covers the other usual suspects.
Refix, replace or reflash: what the repair actually involves
Not every flashing leak means new flashing. What we do depends on what we find once we’re up there.
Refixing what’s already there
If the flashing itself is sound but has pulled out of its mortar joint or lifted at the fixings, we clean off the old sealant, rake out the joint, reseat the flashing and seal it properly. This is the smallest version of the job and often all that’s needed.
Replacing a section
Split, rusted or badly fatigued flashing gets replaced. On a metal roof we make up new flashing in Colorbond or Zincalume to suit the roof, and where old lead is sitting above steel we’ll recommend it comes out rather than being patched.
Reflashing a chimney properly
When a chimney has been patched over and over, the honest answer is usually to strip it back and reflash it as a set: apron, steps, back gutter and counter flashing working together. It’s more work up front, but it ends the cycle of a new stain every winter. Sealant still has a place here, as a backup at the edges. It just shouldn’t be the thing keeping the water out.
This is everyday work for our roof repair team on the Peninsula, on both tile and metal roofs. If we find the chimney itself is the problem, with porous brick or a cracked chimney top, we’ll tell you plainly rather than reflash something that will keep leaking for another reason.
Get the flashing checked before the ceiling pays for it
A flashing leak rarely fixes itself, and every storm it lets through puts more water into the ceiling lining and the timber above it. If you’ve got a stain near a chimney, wall or pipe, ask us to check your flashings and we’ll tell you whether it needs refixing, a new section or a full reflash.
Straight answers about leaking flashing
Can roof flashing be repaired rather than replaced?
Often, yes. Flashing that has lifted or pulled out of a mortar joint can usually be cleaned up, reseated and sealed. If the metal is split, rusted through or was never long enough to begin with, replacing it is the better repair.
How much does flashing repair cost?
It depends on access, roof type and whether we’re refixing one piece or reflashing a whole chimney, so we price it after seeing the roof. Our post on what drives the cost of fixing a roof leak explains the factors that move the price.
What do roofers use to seal flashing?
The flashing itself does the waterproofing: it’s shaped and lapped so water runs over it and away. A roof and gutter sealant goes on joints and edges as a backup, and counter flashing is set into the mortar joint and sealed. A thick bead of sealant on its own isn’t a flashing.
Can I replace roof flashing myself?
A temporary patch is within reach of a handy homeowner, but working on a roof is genuinely dangerous and tiles crack easily underfoot. Proper flashing also has to be cut, folded and lapped to suit the roof, and the wrong metal can cause corrosion. For anything beyond a stopgap, get a roofer.
Is it normal for a chimney to leak in heavy rain?
No. A properly flashed chimney should stay dry in heavy rain. If it only leaks in a downpour or strong wind, water is getting past the flashing, the back gutter is overflowing, or the brickwork is soaking it up.
Does house insurance cover a leaking chimney flashing?
Policies generally treat sudden storm damage differently from gradual wear, and failed sealant or corroded flashing usually counts as wear. Check your own policy wording and talk to your insurer. Either way, fixing the cause quickly limits the damage inside.
Do roofers fix chimneys?
Roofers handle the flashing and the roof around the chimney, which is where most chimney leaks start. If the brickwork, mortar or chimney top has failed, that can call for a bricklayer as well, and we’ll tell you if that’s what we find.
