Roof flashing repairs: why flashings fail, and what fixing them involves

Roof flashing repairs fix one of the most common sources of roof leaks, and one of the most commonly botched. A flashing is the piece that seals a join: where the roof meets a wall, a chimney, a skylight, a vent or another roof. Roof surfaces are good at shedding water. Joins are where water gets in, and flashings are what stop it.

This guide covers the main types of flashing, why they fail, the signs you can spot from the ground, and what a proper repair involves.

The main types of flashing

Apron flashings. Where a roof runs up to a wall or a higher roof, such as a lean to or extension meeting the main house. The apron sits over the roof surface and turns up the wall.

Step and soaker flashings. Where the side of a roof slope meets a wall, such as along a chimney or the side of a second storey. They step up the wall alongside the tiles or sheets.

Counter flashings. Fixed into the wall or chimney above the apron or step flashing, covering its top edge so water cannot get behind it.

Chimney flashings. A combination of apron, step and back flashings around all four sides of a chimney.

Penetration flashings. Around vents, flues, pipes and skylights that come up through the roof.

Barge and ridge flashings. On metal roofs, these cap the edges and the top of the roof.

Valley flashings. The channels where two roof slopes meet, often called valley irons on a tiled roof.

Why flashings fail

Age and corrosion. Older flashings, particularly galvanised steel, rust through over decades. Lead lasts longer but can split or be lifted by wind.

Cement and mortar flashings. On many older Melbourne homes, joins were sealed with a cement fillet rather than a proper flashing. As the house moves, the cement cracks and pulls away, and water runs straight into the gap.

Sealant used instead of a flashing. A bead of silicone or a smear of roofing mastic looks like a fix and lasts about as long as a summer or two. Sun breaks it down, it shrinks and lets go, and the leak returns.

Movement. Walls, chimneys and roofs move at different rates as they heat and cool. A flashing that was not fixed to allow for that tears or pulls out.

Poor original work. Flashings that are too short, not turned up the wall far enough, not tucked under the course above, or not fixed into the mortar joint.

Wind. Loose flashings on metal roofs can be lifted by wind, and each gust levers them further.

Damage from other trades. Antenna, air conditioning and solar installers working around flashings sometimes bend or cut them.

Signs of a flashing problem

You can spot a lot without getting on the roof. Look for:

• Stains on a ceiling or wall next to a chimney, skylight or extension join
• Water inside around a skylight or flue during rain
• Cracked or missing cement where the roof meets a wall or chimney
• Flashings that look bent, lifted, rusted or loose from the ground
• Lots of silicone visible around a join, which usually means an earlier patch
• Leaks that only show up in wind driven rain from one direction
• Damp patches on an internal wall below where an extension meets the house

What a proper repair involves

Trace the leak first. Water can run along a rafter or batten before it shows up inside, so the stain may not be under the flashing at fault. We check the roof space, then the outside, and confirm where the water is getting in.

Photograph the fault. You see exactly what has failed before we touch it.

Remove the failed material. Cracked cement fillets, old sealant and rusted flashings come out. Putting new over old rarely works.

Form the flashing to fit. A good flashing is shaped to the join: turned up the wall far enough, dressed down over the tiles or sheet profile, and long enough to cover the joint properly.

Fix it properly. Counter flashings are let into the mortar joint or fixed to the wall so water cannot get behind them. Fixings allow for movement where needed.

Photograph the finished repair. Before and after photos go into your report.

When a flashing repair is roof plumbing

Under Victorian practice, some flashing work, particularly on metal roofs, around plumbing penetrations and in gutters, falls under roof plumbing and needs a licensed roof plumber. Whoever does the work, a careful trace and clear photos of the fault are what make sure the right thing gets fixed.

Flashings on older inner north homes

Victorian terraces and cottages in suburbs like Brunswick and Northcote often have chimneys, parapets and party walls, and many still rely on cement fillets that have cracked. Extensions added over the decades create new joins with the original roof, and those joins are one of the most common leak sources we trace. If your home has any of these, flashings are worth checking before storm season.

Book a flashing inspection

If you have a leak near a chimney, skylight or extension, or you can see cracked cement or silicone patches from the ground, we will get on the roof, trace it and photograph what we find. The inspection is free. Call 0420 541 479 or send a quote request and we will call you back within 2 hours, Mon to Sat, 7am to 6pm.