Roof cleaning is the most misunderstood job on a Sydney home. It's sold as a cosmetic service, priced like a driveway clean, and performed at heights that make it one of the more dangerous trades going.
This guide covers what actually happens on a roof, when it's worth doing, and how to separate an operator who will look after your roof from one who will cost you a repointing bill.
Why Sydney roofs get dirty so fast
Three factors combine here: humidity, tree canopy and mild winters. Sydney rarely gets cold enough to knock organic growth back, so mould, moss and lichen keep working year-round.
The Upper North Shore, Lane Cove valley and the leafier parts of the inner west are the worst affected because heavy gum canopy keeps roofs damp and drops constant organic debris. Coastal suburbs deal with salt instead, which is harsher on metal roofs and fixings.
What lichen actually does to a tile
Lichen isn't dirt sitting on the surface — it's a living organism that bonds into the tile's coating and holds moisture against it. On cement tiles that accelerates the breakdown of the coloured surface coating, leaving porous grey tile underneath that absorbs water.
On terracotta, lichen is more of a surface and drainage issue than a structural one, but it still blocks valleys and gutters as it breaks down. Blocked valleys are one of the most common causes of internal water damage we see.
Tile, terracotta and Colorbond need different methods
Sound cement tile handles correct-pressure cleaning. Old, spalling cement tile does not — it needs lower pressure and a longer chemical dwell. Terracotta is more brittle and chips at the edges under aggressive cleaning. Colorbond and Zincalume need low pressure and care around fixings, and any rust needs addressing separately.
- Cement tile (sound): treatment then correct-pressure clean
- Cement tile (worn/porous): treat, low pressure, consider recoating
- Terracotta: treatment, controlled pressure, no coating
- Colorbond / metal: soft wash, rust assessment, gentle rinse
- Slate: specialist handling — brittle and easily broken underfoot
How often should you clean a Sydney roof?
Every three to five years suits most homes. Under heavy tree canopy, on the North Shore, or close to the coast, every two to three years is more realistic. If lichen is visible from the street, you're already past due.
Cleaning also serves as an inspection. Cracked tiles, failed pointing and rusted valleys are all found while a roof is being cleaned, and they're all far cheaper to fix before water gets inside.
Why DIY roof cleaning is a bad trade
A wet tile roof is one of the most slippery surfaces you will ever stand on, and roof work sits squarely inside working-at-heights regulations for good reason. Beyond the fall risk, foot traffic on the wrong part of a tile cracks it, and a domestic pressure washer in inexperienced hands will strip coating and drive water under the tiles into your ceiling.
Questions worth asking before you book
Any decent operator will answer all six without hesitating.
- What safe-work documentation do you provide?
- How will you protect the property and surrounding areas?
- How do you manage waste water and roof debris?
- Will you inspect and report on tiles, pointing and valleys?
- Do you clear gutters and valleys as part of the job?
- What pressure and treatment will you use on my specific roof type?
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