Getting rid of roof moss, lichen & black stains in Canberra

If your roof has gone green, grey-black or crusty with lichen, you're not alone — it's one of the most common jobs we're called out for across the ACT. Canberra's cold, damp winters and shaded southern roof faces are ideal conditions for moss, lichen and algae. Here's what's actually happening up there, and how to fix it without wrecking the roof.

Why Canberra roofs grow moss and black stains

Three culprits, and they often turn up together:

• Algae (the black streaks) — a hardy organism that feeds on airborne dust and the limestone filler in some tiles. It shows up as dark stains, worst on the shaded side.
• Moss (the green fuzz) — thrives in the cool, damp joints between tiles and holds water against the roof long after rain.
• Lichen (the crusty spots) — the toughest of the lot. It roots into the tile surface and leaves marks even after the growth is gone.

Beyond looking tired, they matter: moss lifts and holds moisture, blocks valleys and gutters, and over years can shorten the life of the roof.

Why blasting a roof at full pressure is a mistake

It's tempting to hit a mossy roof with maximum pressure, but on tile and Colorbond that's how you cause damage: high pressure strips the protective glaze off concrete tiles, forces water under the laps, and can void roof warranties. The moss comes off, but the tiles are left more porous — so it grows back faster.

The right approach is soft washing: a low-pressure application of a treatment that kills the moss, lichen and algae at the root, which is then gently rinsed. It's safer for the roof and far more effective long-term.

The process that actually lasts

1. Inspect — check tile condition, ridge capping and gutters first.
2. Treat — apply a biocide soft-wash that penetrates and kills the growth.
3. Clear — remove loosened moss and flush gutters and valleys.
4. Protect — an optional preventive treatment keeps regrowth away for much longer.

Because lichen roots into the surface, some staining can take weeks to fully weather away after treatment — that's normal, and better than gouging the tile to force it off on the day.

How often should you clean a Canberra roof?

For most homes, every 2–4 years keeps things under control, or sooner on heavily shaded, tree-lined blocks. Pairing a roof clean with a gutter clear in the same visit is the cheapest way to do it.