It usually starts with a phone call that goes something like this: “I was cleaning the gutters and the roof has gone orange in patches. Is it finished?” Sometimes the answer is yes. More often it is no, and the roof has years left in it once the rust is dealt with properly. The trick with rusted roof repair is working out which kind of rust you have, because a few freckles near the screws and a sheet you could push a screwdriver through are completely different jobs.
Here on the Mornington Peninsula the question comes up more than it does inland. Salt air off the bay and Bass Strait settles on every roof, and it does not wash off evenly.
Not all rust is the same problem
Tiny orange dots scattered across the sheets
This one surprises people. A spray of small rust spots, often on a newer roof, is usually swarf: the hot metal filings that fly off when a roofer cuts sheets or flashings with a grinder. If nobody sweeps them off, they rust on the surface within weeks and leave stains. The roof itself is often fine underneath. The filings need to be removed and the marks assessed, but this is rarely a sign the sheet is failing.
Rust around the screw heads
Roof screws have a rubber washer and a coated head. Over time the coating wears, the washer perishes in the sun, and water sits around the hole. You will see an orange ring around each screw, and eventually the screw loosens and lets water in. On older roofs we often find the screws have rusted well before the sheets have. Replacing them with new screws suited to coastal conditions is a common and relatively contained fix.
Rust along the sheet ends and overlaps
The cut edge at the bottom of each sheet, where it hangs over the gutter, has no protective coating on the raw edge. The same goes for the laps where one sheet sits over another and moisture gets trapped between them. Rust here tends to creep back from the edge. Caught early it can be treated. Left alone, the ends go thin and crumbly and start dropping flakes into the gutter.
Rust in the spots the rain never reaches
Metal roofs rely on rain to rinse salt off. Areas that stay dry, such as under a wide eave, behind a parapet, or under a second storey overhang, collect salt and never get washed. We see these sections rust badly on homes where the open parts of the roof still look good.
Rust caused by the wrong metal touching the roof
Certain metals react with Zincalume and Colorbond steel. Copper is the usual culprit: water dripping off a copper pipe or an air conditioner condensate line can eat a stain into the sheet below. Lead flashings and some old TV antenna fittings cause the same kind of damage. The fix is to remove or redirect the source as well as deal with the rust, or it simply comes back.
Holes and sheets that have rusted through
This is the serious end. If you can see pinpricks of daylight from inside the roof space, or rust has left lacy holes in the sheet, the steel is gone in that area. Paint and sealant will not bring it back.
A quick way to tell surface rust from structural rust
You do not need to climb on the roof to get a rough idea, and please do not if you are not used to it. Metal roofs are slippery, older sheets can give way underfoot, and falls from roofs cause serious injuries.
From a ladder at the gutter line, look at the bottom edge of the sheets. Staining with a firm surface is usually treatable. Flaking, bubbling or edges that crumble when you touch them mean the metal is losing thickness. Then go into the roof space on a sunny day with a torch off. Any specks of light coming through the sheets, or rusty drip marks on the timber or sarking, tell you the rust has gone right through.
What the repair actually involves
For surface rust, the work is cleaning back the affected area to sound metal, treating it, priming it with a product made for metal roofs, and then painting to match. Done badly, with paint straight over loose rust, it lifts within a season or two and you are back where you started.
Rusty screws get swapped out. Sheet ends that have started to corrode can be treated if there is still enough good metal; if not, it may be possible to replace just the worst sheets. Swarf gets cleaned off. Copper sources get relocated. Our metal roof repair service covers all of this, and we will tell you plainly whether a section is worth treating or needs new steel.
Holes are where we push back on quick fixes. A blob of silicone or a stick-on patch over a rust hole might keep the water out for a while, but rust keeps working under it. We treat those as a temporary measure to get you through until the sheet is replaced.
When patching stops making sense
Repair is good value when the rust is local: a few sheets, one side of the roof, the dry patch under the eave. It stops being good value once rust is showing up across most of the roof, the sheet ends are failing all the way along, or the sheets have rusted through in several places. At that point you are paying to fix one area while the next one is already going.
That is usually the moment to look at new sheeting. If you are weighing up which steel to go back with, our guide to choosing between Zincalume and Colorbond near the coast covers how each one handles salt air. For new roofs and restorations we provide a 10-year materials and workmanship warranty, which is worth factoring in against repeated patch repairs.
There is a middle ground too. A roof with scattered surface rust but sound steel is sometimes a good candidate for a full clean, rust treatment and recoat. We cover when that is worthwhile in our post on whether repainting a metal roof pays off. It is not the answer for a roof that has rusted through, whatever the brochure says.
Slowing rust down on a coastal roof
You cannot stop salt reaching your roof if you live in Rye, Rosebud or anywhere with a view of the water. You can stop it building up. Hosing down the areas that rain does not reach, every so often, rinses off the salt before it does damage. Keeping gutters clear matters as well, because wet leaf litter sitting against the sheet ends holds moisture right where the metal is weakest.
It also helps to ask any tradesperson working on your roof (solar installers, antenna fitters, air conditioning techs) to sweep off their filings before they leave and keep copper lines from draining onto the sheets. Those two habits prevent a surprising amount of the rust we are called out to look at.
If your roof has started to turn orange and you are not sure what you are looking at, we are happy to come out and take a look. We work across Hastings, Mount Eliza, Mount Martha, Rosebud, Rye and Somerville, and we are open every day from 7am to 7pm. Have a read of what our metal roof repairs involve, or get in touch for an honest assessment of whether yours can be saved.
Common questions about rusted roofs
Can a rusted metal roof be repaired?
Yes, in most cases where the rust is on the surface or limited to certain areas. Treating the rust, replacing perished screws and swapping out the worst sheets can add years to the roof. Once the steel has rusted through across large parts of the roof, replacement is the more sensible spend.
Can minor rust be repaired?
Minor surface rust is the easiest type to fix. The area is cleaned back to sound metal, treated, primed and painted. The key is dealing with it before it eats into the thickness of the sheet.
Will my metal roof rust?
Any steel roof can rust if its protective coating is damaged or salt is left sitting on it. Coastal homes, areas under eaves that rain does not wash, cut edges and spots where copper drips onto the sheets are the most common trouble areas. Regular rinsing and clean gutters slow the process down a lot.
What paint can I use on a rusted metal roof?
Use a rust treatment and a primer made for metal roofing first, then a roof paint designed for steel. Ordinary house paint or paint applied over loose rust will peel. Painting is only worth doing if the metal underneath is still solid.
Why is my new roof already showing rust spots?
Small orange dots on a newer roof are usually metal filings left behind after cutting, not a fault in the sheet. They rust on the surface and stain. Having them cleaned off promptly usually prevents lasting damage.
