A flashing roof detail is the bent metal strip that seals every joint, edge and penetration where roof sheets meet a wall, chimney, valley or each other. Most Sydney homes use Colorbond steel flashing, and prices depend on girth, length and how many bends the roofer has to fold (indicative — get itemised quotes).
This guide covers the types of roof flashings, how corrugated roof flashing differs, Colorbond flashing prices and the mistakes that cause leaks. For the full catalogue of shapes, see our roof flashing types guide.
Key points
- A flashing roof joint fails long before the sheets do, so most roof leaks trace back to flashing rather than the roofing itself.
- Colorbond steel flashing suits Colorbond roofs because the metal, coating and expansion rate all match.
- Silicone is a short-term patch only; proper repairs replace or re-lap the flashing and refix it correctly.
- Flashing work happens at the roof edge, so book a licensed roofer rather than climbing up yourself.
What is a flashing roof detail?
Flashing is thin sheet metal, usually folded to suit the joint, that directs water over the top of a junction and back onto the roof surface.
| Term | What it means | Why it matters |
|---|---|---|
| Roof flashings | Folded metal strips fitted at joints, edges and penetrations | They shed water away from gaps that sheeting alone cannot seal |
| Flashing metal | The sheet material used, such as Colorbond steel, Zincalume, aluminium or copper | Mixing metals starts corrosion, so match the flashing to the roof |
| Tin roof flashing | Everyday name for steel flashing on an iron roof | Tradies and suppliers use the term loosely, so describe the joint when you order |
| Girth | The unfolded width of the metal strip | Girth drives both the material cost and how far the flashing reaches under the sheets |
| Lap | The overlap where two lengths of flashing meet | A short or unsealed lap is the most common place for a leak to start |
Types of roof flashings
Each junction needs its own shape, and a few of them have their own guides on this site.
| Type | Where it goes | What it does |
|---|---|---|
| Apron flashing | Where a roof meets a higher wall | Covers the joint and sheds water onto the roof sheets |
| Step flashing | Along a sloping wall or chimney side | Follows the slope in stepped sections so water cannot track behind |
| Valley flashing | Where two roof planes meet | Carries heavy runoff to the gutter, so it must be wide and continuous |
| Ridge and hip capping | Along the top and sloping corners | Seals the sheet ends; see our Colorbond ridge capping guide and the ridge capping guide |
| Barge capping | Along the gable end of the roof | Protects the sheet edge from wind-driven rain; see our barge capping guide |
| Penetration flashing | Around vents, pipes and skylights | Seals the hole with a boot, collar or custom fold |
| Headwall flashing | Where a lower roof meets an upper wall | Stops water tracking down the wall behind the cladding |
Corrugated roof flashing and steel roof flashing
Corrugated roof flashings have to deal with the wave profile, which leaves small gaps under the sheet where it meets a flat flashing.
- Profile fillers: use foam or metal closures that match the corrugation so wind-driven rain and insects cannot enter under the flashing.
- Lap direction: lap flashing over the sheet on the high side, then fix through the crest, not the valley, so water cannot sit around the screw.
- Steel roof flashing: pair Colorbond flashing with Colorbond sheets and Zincalume with Zincalume, since each coating wears and expands differently.
- Corrugated roof flashing at walls: turn the top edge into a groove or under the cladding, and seal only the top edge, never the lap between sheets.
- Old iron roofs: rust often hides under the flashing, so check the sheet beneath before you reseal anything.
- Fixings: use screws made for the metal and the climate, because mismatched fixings rust and streak the flashing within a couple of seasons.
Flashing for roof junctions: choosing the right metal
Flashing metal should match the roof, the coast and your budget. This table compares the common options.
| Metal | Best for | Watch out for |
|---|---|---|
| Colorbond steel | Colorbond and painted roofs where the colour should match | Cut edges need care near the coast, where salt attacks bare steel |
| Zincalume steel | Unpainted metal roofs and hidden junctions | Do not mix with copper or lead runoff, which speeds corrosion |
| Aluminium | Coastal homes and light-duty trims | Soft and easily dented; read our aluminium flashing guide |
| Galvanised steel | Older roofs and budget repairs | Coating wears sooner than Colorbond in salt air |
| Copper | Heritage work and feature junctions | Never lets runoff touch zinc or aluminium sheets |
| Polycarbonate roofing trims | Patios and carports with clear sheets | Needs flashing and sealing parts made for the sheet; see our polycarbonate roofing guide |
If you only need a quick explainer of the basics, our general flashing guide covers the fundamentals.
Colorbond flashing prices and flashing roof cost
Colorbond flashing prices change with girth, length, bends and the height of the job, so treat every line below as a starting point.
| Item | What drives the price | Typical range |
|---|---|---|
| Colorbond flashing, supply only | Girth, colour and number of folds | Low cost per lineal metre (indicative — get itemised quotes) |
| Standard apron or barge flashing, installed | Length, access and sheet type | Mid range per lineal metre (indicative — get itemised quotes) |
| Valley replacement | Length, roof pitch and sheet removal | Upper range per valley (indicative — get itemised quotes) |
| Chimney or skylight flashing | Custom folding and weathering work | Quoted per job (indicative — get itemised quotes) |
| Two-storey or steep roof | Scaffold, edge protection and extra labour | Adds to the quote (indicative — get itemised quotes) |
| Full re-flash during a reroof | Number of junctions and cut-in work | Often cheaper per metre than a standalone job (indicative — get itemised quotes) |
- Ask for itemised quotes: flashing should be a separate line from sheeting so you can compare like with like.
- Combine jobs: replacing flashing while the roof is already open saves access and labour costs.
Signs your flashing roof joints need attention
- Stains on ceilings near walls: brown rings beside a chimney or a wall often show a failed apron flashing above.
- Lifted or bent edges: strong wind can peel an unsupported flashing back, so look for gaps along barges and ridges.
- Rust streaks and white bloom: corrosion around laps and screws means water is lodging there or two metals are touching.
- Lumps of old sealant: layers of silicone usually mean someone has patched the leak several times without fixing the cause.
- Daylight in the roof space: if you can see light at a junction from inside, water gets in as easily as light does.
- Damp or mouldy timber: check rafters and wall plates near the junction, because slow leaks rot framing long before the ceiling stains.
Safety and licensing for flashing work
- Stay off the roof: sheeting is slippery and a fall from height is a leading cause of serious home maintenance injuries.
- Book a licensed roofer: flashing replacement involves lifting sheets, working at the edge and often needs edge protection or scaffold.
- Suspect asbestos: older fibre-cement sheets and eaves can contain it, so do not drill, cut or scrub them; get a licensed assessor first.
- Check council rules: heritage areas and bushfire-prone blocks may restrict materials, so confirm before ordering.
- Keep paperwork: ask for the roofer’s licence number and a written workmanship warranty before work begins.
Common flashing mistakes to avoid
- Sealing instead of lapping: a bead of silicone over a short lap cracks within a season or two and hides the real problem.
- Mixing metals: copper, lead or untreated steel touching a Colorbond roof sets up corrosion at the contact points.
- Fixing in the valley: screws through the low point of the sheet let water sit around the fixing and leak.
- Skimping on girth: narrow flashing cannot lap far enough under the sheets, so wind-driven rain gets behind it.
- Ignoring the sheet beneath: new flashing over rusty or damaged sheeting only buys you a short reprieve.
- Skipping closures: gaps under flashing on corrugated roofs invite rain, insects and birds into the roof space.
Flashing roof FAQs
What is the best flashing metal for a Colorbond roof?
Colorbond steel flashing in the same colour is the usual choice, because the coating and expansion rate match the roof. Near the coast, aluminium is a sound alternative for light trims. Avoid copper and lead against steel sheets, since runoff speeds up corrosion.
How much do Colorbond flashing prices vary?
Colorbond flashing prices depend on girth, length, folds and access, so two quotes can look very different. Supply-only flashing costs far less than installed work with scaffold. Always ask for itemised quotes that list flashing separately from sheeting and labour.
Can I fix tin roof flashing with silicone?
Silicone can buy you a short wet-weather fix, but it does not cure a failed lap or lifted edge. Proper repairs refix or replace the flashing so water runs over the joint, not into it. A licensed roofer should do any work at height.
Does corrugated roof flashing need special closures?
Yes. The wave profile leaves gaps under flat flashing, so use profile-matched foam or metal closures. Without them, wind-driven rain, birds and insects get under the flashing, and sealant alone will not hold for long on a Sydney roof.
Getting flashing roof repairs in Sydney
A flashing roof repair works best when the sheets beneath are sound and the new metal matches the roof. TQN Construct’s licensed roofers inspect, repair and replace flashing across Sydney with itemised quotes and workmanship cover. Book a free roof inspection and quote.
