Why some Melbourne roofs go green and others don't
A rain gradient from west to east
Bureau of Meteorology averages give Melbourne Airport 515.5 mm a year and Laverton 540.9 mm, against 736.7 mm at Mornington and 1,164.2 mm at Mount Dandenong. Melbourne sits in a rain shadow between the Otway and Macedon Ranges, which is part of why the west stays drier. More rain and slower drying mean more moss.
Shade and damp in the ranges
The Dandenong Ranges get 1000 to 1500 mm a year, rising with elevation, under tall mountain ash forest. Above 500 m, snow typically falls a few times a year. Roofs under that canopy stay damp for long stretches, and moss and lichen take hold fast.
Postwar homes and asbestos
The Housing Commission of Victoria built tens of thousands of homes from the late 1940s to the early 1970s, and plenty of private homes went up in the same years. EPA Victoria says houses built before 1990 are likely to have some asbestos, and lists roofing tiles among the products that can contain it.
Salt near the bay
Rain keeps most of a metal roof clean, but BlueScope says areas rain doesn't reach, like the underside of eave gutters, should be washed at least six-monthly, or three-monthly where there's marine salt spray. That's worth adding to the routine for homes near Port Phillip or the ocean coast.
Never pressure clean an asbestos roof
It's illegal in every Australian state to use high-pressure water on asbestos materials. Pressure cleaning asbestos roofs has spread fibres to neighbours' yards, footpaths and stormwater, with clean-up bills in the hundreds of thousands of dollars. If your roof might be asbestos cement, don't let anyone clean it until it's been checked. Start with is my roof asbestos?
How a tiled or metal roof should be cleaned
Monier, which makes concrete and terracotta tiles, strongly advises against pressure washers on roof tiles because they can damage them, and recommends a professional roof cleaner instead. It also says moss and lichen on terracotta only grow on the surface and don't affect the tile itself, so on a sound terracotta roof, cleaning is mostly about looks and keeping debris out of the gutters.
On metal, a gentle wash is usually enough. If the roof is about to be coated, cleaning becomes part of the prep, and that's a restoration or painting job rather than a stand-alone clean.
Questions to ask a roof cleaner
- What method will you use on my roof, and at what pressure?
- Is my roof possibly asbestos cement, and have you checked before quoting?
- Which moss treatment do you use, and where does the run-off go? I have a garden and a water tank.
- Who pays if tiles crack during the clean?
- Will you clear the gutters and downpipes afterwards?
What we'd tell a friend
If you're in the drier west and the roof just looks a bit grubby, we'd leave it. In the hills or the wetter south-east, we'd have moss treated gently every few years and the gutters cleared after, rather than blasting it off. And on any home old enough to have asbestos, we'd rule that out before anyone touches the roof. Our national roof cleaning page covers methods, and the Melbourne hub covers the bigger local picture.
Want a roofer to take a look?
Tell us the job and your postcode. We match it with a Find My Roofer certified roofer who specialises in that kind of work, and they call you to quote. Your number goes to them alone.
