Roof flashing repair that stops the leak at the join

A flashing is a strip of metal that bridges the gap between the roof covering and anything that interrupts it. On a Melbourne house there are four main kinds. An apron flashing runs along the bottom of a wall where a lower roof meets it, and along the front of a dormer or a box. A step flashing climbs the side of a wall in short overlapping pieces, each one tucked into a brick course or behind the cladding. A penetration flashing seals a pipe, vent, flue, whirlybird or exhaust cowl where it comes up through the roof. A valley flashing is the long channel where two roof planes meet, and it has its own page.

Every one of them is a join between two materials that move differently. Brick expands and contracts at one rate, roof tiles at another, Colorbond steel at a third. The mortar that holds an old flashing in a brick chase cracks. Lead fatigues after decades of hot and cold. Galvanised steel on a home from the 1960s or 1970s rusts from the underside where damp litter sits against it. Sealant that was only ever meant to be a backup dries and lets go.

That is why the flashings are the first thing our roof plumber checks on a leak call. A cracked tile or a loose sheet is easy to see. A flashing that has lifted three millimetres is not, and it is a common cause.

Apron flashings. The usual failures are a lifted top edge where the flashing was set into a mortar chase, a split in old lead, or a flashing that was never turned up high enough under the cladding. The repair is to cut a clean chase, fit a new upstand with a proper overlap onto the roof, and seal the chase with a flexible sealant rather than mortar that will crack again.

Step flashings. These fail one piece at a time. A single short piece that has slipped or rusted is replaced and re-lapped over its neighbours. When most of the run is gone, the whole side is re-flashed so the laps all face the right way.

Penetration flashings. Vents, whirlybirds, plumbing stacks, flues, exhaust cowls and solar conduits each need a flashing shaped to them. A rubber boot flashing suits a round pipe on a metal roof; a soaker flashing dressed into the tiles suits a tile roof; a whirlybird needs a base flashing that sheds water all the way round. The wrong flashing, or a good flashing installed without a back tray, is a common source of new leaks on otherwise sound roofs. If you want a whirlybird fitted properly in the first place, our whirlybird installation page covers it.

Valley flashings. Rusted or dammed valleys are covered on our valley iron replacement page.

Chimney flashing is a different job with its own page: chimney flashing repair.

A flashing can be repaired when the metal is sound and the failure is in how it sits. A lifted edge is re-dressed and re-fixed. An open mortar chase is cut back and re-sealed. A single rusted step piece is swapped. A boot flashing with a cracked collar is replaced with a new one of the right size. These are quick jobs and we do them the same visit where we can.

A flashing is replaced when the metal itself has gone. Rust that has perforated the steel, lead that has cracked along a fold, a flashing that was cut too short to ever work, or a run that has been sealed over so many times there is more silicone than metal. Sealing over failed metal buys a few months at best, and we will say so rather than do it.

New flashings are made from Colorbond steel matched to the roof colour where the roof is steel or where a coloured flashing is wanted, or from lead where a period tile roof needs a flashing that can be dressed tightly into an irregular shape. We do not put dissimilar metals in contact or let one drain onto another, because that is how a new flashing starts rusting in its first year. Every job is photographed before we start and again when it is finished, so you can see the metal, the laps and the seals without climbing a ladder.

The home changes the job. On a brick veneer house the wall flashings are set into a chase cut in the mortar joint, so the repair means grinding a clean chase and sealing a new flashing into it. On a weatherboard home the flashing tucks up behind the bottom board, so the board comes off, the flashing is replaced, and the board goes back. On a period home with a slate or terracotta roof, the original flashings are often lead and were dressed by hand; the replacement is dressed the same way so it sits tight to the tile profile.

Newer estate homes have their own pattern: a lot of penetrations added after the roof was built. Ducted heating flues, bathroom exhaust ducts, solar conduits, NBN and antenna mounts, all pushed through by different trades with whatever flashing was in the van. Those are the roofs where we find three or four small flashing faults on one visit and fix them together.

All flashing work is carried out by licensed roof plumbers. If the leak turns out to be a cracked tile or a blocked gutter rather than the flashing, we tell you that on the day, because the point is a dry ceiling, not a flashing invoice.