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, what it's costing you, 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.

Canberra makes all three worse than most Australian cities. Winter here is genuinely cold and damp, southern roof faces can go months without direct sun between May and August, and the mature tree canopy across the established suburbs keeps roofs shaded and drops organic matter onto them year-round. Frost adds a second problem: moss holds water in the tile surface, and water that freezes and thaws repeatedly accelerates the breakdown of the tile itself.

What it's actually costing you

Roof growth isn't only cosmetic. Left alone it does measurable damage:

• Moisture retention. Moss acts as a sponge, holding water against tiles that are designed to shed it — which is what accelerates surface degradation and, with frost, spalling.
• Blocked valleys and gutters. Shed moss and lichen wash into the valleys and gutters and pack down into sludge. That causes overflow into eaves and walls, and it's a fire-season ember risk.
• Shortened roof life. A porous, growth-covered tile absorbs more water and degrades faster than a clean one. On a roof that should last decades, that's an expensive acceleration.
• Presentation. A green-black roof is one of the first things a buyer or valuer registers, and it reads as deferred maintenance across the whole property.

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.

It also tends to dislodge the mortar bedding and pointing under the ridge capping, which is the part of a tile roof most likely to already be near the end of its life. A blast that "cleans" a roof and loosens the capping has cost you far more than it saved.

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 general principle — match the method to the surface — is covered across every material in our soft washing vs pressure washing guide.

What your roof is made of changes the job

Roof type	Approach	Watch out for
Concrete tile	Soft wash + biocide	Pressure strips the surface glaze permanently
Terracotta tile	Soft wash, low pressure	Older tiles are brittle and break underfoot
Colorbond / metal sheeting	Soft wash, soft brush	Denting, and water forced up under laps and flashings
Slate	Soft wash only, minimal foot traffic	Cracks and delaminates easily; specialist work
Cement or fibro sheeting (pre-1990)	Do not clean — assess first	May contain asbestos; high-pressure and abrasive cleaning of asbestos-cement is prohibited

That last row matters in Canberra, where plenty of housing stock and outbuildings predate 1990. If there's any chance a roof or shed is asbestos cement, it must not be pressure cleaned or abrasively cleaned — doing so releases fibres and is prohibited under work health and safety rules. Get it identified before anyone touches it.

The process that actually lasts

1. Inspect — check tile condition, ridge capping, flashings and gutters first. This is also when broken tiles get found, which is worth knowing regardless.
2. Treat — apply a biocide soft-wash that penetrates and kills the growth at the root rather than knocking the top off it.
3. Clear — remove loosened moss and flush the valleys, gutters and downpipes so the debris doesn't just relocate into your drainage.
4. Protect — an optional preventive treatment keeps regrowth away for much longer, and is the single biggest factor in how long the result lasts.

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.

What to expect afterwards

When	What you'll see
On the day	Loose moss and lichen gone; black staining noticeably lighter
2–4 weeks	Dead growth continues to weather off with wind and rain
1–3 months	Lichen residue and remaining stains fade out; the roof reaches its final colour
2–4 years	Regrowth starts to become visible again, longer if treated

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 — and it's the sensible order, because cleaning a roof sends debris straight into the gutters.

Cleaning vs restoration — which do you need?

These get conflated, and the price difference is enormous. Cleaning is for a structurally sound roof that's dirty, mossy or stained: a few hundred dollars, done in a day. Restoration — repointing, rebedding the ridge capping, replacing broken tiles and recoating — is for a roof with failing mortar, widespread cracking or a coating that's broken down, and it runs into the thousands.

Always clean first. A roof that looks beyond saving under a decade of lichen very often turns out to be perfectly sound underneath, and you can't properly assess the tiles until you can see them. Anyone quoting a restoration on a roof they haven't cleaned is guessing.

What it costs in Canberra

Roof cleaning and treatment typically runs $399–$900. Single-storey homes start around $399; the number moves with the roof's footprint, pitch, storeys, access and how much growth is up there. Adding gutters, a house soft-wash or solar panel cleaning to the same visit is materially cheaper than separate bookings, since most of the cost is mobilising the equipment and setting up safely. Full ranges are in our Canberra pressure cleaning cost guide.

Please don't do this one yourself

We say this on very few jobs, but roof work earns it. Wet tiles and metal sheeting are extraordinarily slippery, older tiles crack underfoot without warning, and a fall from roof height is life-changing. Beyond the safety issue, the damage a well-meaning DIY roof clean does — stripped glaze, loosened capping, water pushed under the laps into the ceiling space — regularly costs more than a decade of professional cleans. If you take one thing from this guide, make it this one.

FAQs

How much does roof cleaning cost in Canberra?

A roof clean and treatment typically runs $399 to $900. Single-storey homes start around $399; double-storey, steeply pitched or heavily overgrown roofs sit at the upper end because of the extra access equipment and time. Booking a gutter clear in the same visit is the cheapest way to do both.

Can you pressure wash a roof?

You can, and you shouldn't. High pressure strips the protective glaze off concrete tiles, forces water up under the laps and into the roof space, dislodges ridge capping and bedding, and can void roofing warranties. It leaves tiles more porous than before, so the moss returns faster. Roofs are soft washed at low pressure with a biocide instead.

Does roof cleaning damage tiles?

Soft washing doesn't. High-pressure blasting does — it removes the surface glaze on concrete tiles, which is the layer that resists water absorption and regrowth. Damage also happens from foot traffic on brittle or older tiles, which is why roof work needs someone who knows where to walk.

How long does roof moss treatment take to work?

The roof looks better immediately once loose growth is cleared, but a biocide keeps working for weeks. Lichen in particular roots into the tile surface, and the residue weathers away gradually over one to three months rather than lifting off on the day. That is normal, and preferable to gouging the tile to force it off.

How often should a roof be cleaned in Canberra?

Every two to four years for most homes. Heavily shaded, tree-lined or south-facing roofs need it closer to every two years, because they stay damp through the ACT's cold winters. Applying a preventive treatment at the end of a clean stretches the interval considerably.

Can I clean my own roof?

We'd advise against it. Roof work is the single most dangerous job around a house — wet tiles and metal sheeting are extremely slippery, brittle tiles break underfoot, and falls from roof height cause serious injury. Add the risk of damaging tiles or bedding, and it is not a job that rewards DIY.

Should I clean or restore my roof?

Cleaning is the right answer if the tiles are sound and just dirty, mossy or stained. Restoration — repointing, rebedding and recoating — is for roofs with failing ridge capping, widespread cracking or a coating that has broken down. A clean is a few hundred dollars; a restoration is thousands, so it is always worth cleaning first to see what is underneath.