Is it a good idea to pressure wash a roof?
Mostly not. Concrete tile makers advise against pressure washers because the jet can damage tiles, stone-chip metal tile makers say water blasting isn’t recommended for their roofs, and the asbestos regulations prohibit high-pressure spraying of any roof containing asbestos. A soft wash avoids all three problems: the cleaning solution does the work and the water pressure stays low, so the surface comes through intact.
Blasting is also a shorter fix than it looks. It removes the visible growth, but it isn’t designed to kill the spores left in joints and pores, so regrowth can start again quickly. A biocide wash kills the growth and the spores together, which is why treated roofs tend to stay clear for longer.
Steel roofing makers do allow careful washing of pre-painted steel, and higher pressure has its place on concrete paths and driveways. For roofs, though, we arrange low-pressure methods as standard. If it’s the driveway or paving you’re after, see water blasting instead.
Roof types on the North Shore and how each is cleaned
Each roof material needs a slightly different approach, and the age of the house matters as much as the material. Long-run pre-painted steel, concrete tiles, clay tiles and decramastic stone-chip tiles are all common on the Shore. All of them clean well with a low-pressure soft wash; what changes is the cleaning solution, how much rinsing is wise and what else needs checking first.
- Long-run pre-painted steel (corrugated or trough iron). Steel makers say rain keeps most of the roof clean and ask for extra washing of the areas rain misses, with water and a sponge or soft brush. Lichen on painted steel should come off promptly, and the industry advice is a chemical treatment rather than scraping.
- Concrete tiles. Porous and slightly rough, so moss and lichen take hold easily. Makers advise against pressure washers. Concrete tiles are often repainted for looks; one tile maker notes a repaint refreshes the colour but doesn’t improve waterproofing.
- Clay (terracotta) tiles. The colour is fired into the tile, so they don’t need repainting, only gentle cleaning. Tile makers warn that even walking on a tiled roof risks cracking tiles.
- Decramastic and other stone-chip metal tiles. Pressed steel tiles with a coated chip finish. Makers of current stone-chip tiles say hypochlorite (bleach) cleaners should never be used on them and recommend quaternary ammonium washes instead. Older decramastic roofs also need the asbestos check below.
Not sure which you have? A photo taken from the street is usually enough for us to tell, and we’ll ask roughly when the house was built.
Decramastic roofs and asbestos: what WorkSafe says
Decramastic and other older roofs need an asbestos check before any cleaning. WorkSafe warns that asbestos-containing material may be present on buildings from before the 2000s, and that decramastic roofing installed before asbestos was phased out may contain it. High-pressure water spraying, including water blasting, must not be used on asbestos roofing or cladding, so these roofs only ever get a low-pressure method.
The WorkSafe safety alert on high-pressure spraying of roofs came out of a real job. A 1970s house with decramastic tiles was water blasted, debris was found across the property and inside the home, and testing confirmed chrysotile asbestos in the tiles. Specialists had to assess the house and it needed remediation.
Here is how we handle it. We ask the age of the house and look at the roof before quoting. Any pre-2000 roof or decramastic roof is quoted for a spray-on treatment or soft wash only. If suspect material turns up during the job, work stops and specialist advice is sought. If you already have an asbestos survey or the building file, tell us what it says.
Where does the wash water go?
Not into the stormwater. Auckland Council’s guidance says contaminants from roof washing must not enter the stormwater system through downpipes or drains, and that even biodegradable detergents are not allowed in. The usual controls are disconnecting or diverting downpipes onto unsealed ground, blocking drains with bungs or covers, and removing leftover wash water.
Ask anyone quoting how they will manage it on your property. The council notes that contractors can be held liable for wash water reaching the stormwater, and that landowners are responsible for work done on their land. A roof that feeds a drinking-water tank needs the tank disconnected before cleaning, and left off until the roof has been rinsed with clean water.
Cleaning a roof before it’s repainted
A roof has to be clean, free of dead growth and dry before any paint goes on, or the new coating sticks to moss and grime instead of the roof. Cleaning is the first stage of every repaint: kill the growth, wash off loose material at low pressure, let the roof dry, then spot-prime bare or rusty patches before the finish coats. Older roofs still get the asbestos check.
If you’re planning a repaint in the next year, mention it when you ask for a cleaning quote. A treatment put on a few months ahead gives dead growth time to weather off, which usually makes the pre-paint wash quicker. Our roof painting page covers the rest of the job.
Problems found while cleaning, such as cracked tiles, sheets rusted through or lifted flashings, are a job for a licensed roofer. We don’t do roof repairs, but we can pass on what the crew saw and point you to someone who does.
Solar panels and the parts of a roof the rain misses
The roof under solar panels, around flues and beneath aerials doesn’t get rinsed by rain, so dirt and growth build up there first. Steel roofing makers call these unwashed areas and, depending on how exposed the site is, recommend washing them by hand anywhere from monthly to every six months. A thorough roof clean includes them, worked gently around panel frames and fixings.
Cleaning the panel glass itself is a separate question: check the panel maker’s guidance on what it can be washed with before anyone touches it.
How often should a roof be cleaned?
For most North Shore homes, every few years, with a look every year or two in between. A stone-chip tile maker suggests a moss treatment every three to five years, or sooner if growth shows up, and a tile maker’s maintenance schedule calls for a moss and lichen check every two years. Roofs shaded by trees or facing south need attention more often than open, sunny ones.
Gutters run on a shorter cycle; tile makers suggest clearing them every six months, more often under trees. The tidy order is a roof treatment first, then a gutter clean once the dead growth has washed down. Signs a roof is due include green or orange patches that keep spreading, black streaks below the ridge, moss along the tile laps and gutters filling with green debris.
If moss and lichen are the main problem, our roof moss and lichen treatment page explains how the spray-and-leave approach works. For the hardware store version, read whether spray-on roof treatments work.
What roof cleaning costs
Published Auckland prices put a roof clean at about $250 to $400 for a small roof, $400 to $600 for an average one of 100 to 200 m², and $550 to $900 for a large roof. A moss and lichen treatment added on the same visit is usually another $100 to $250. Steep pitches, two storeys and heavy growth push the price up, and we confirm it after a look.
| Job | Typical range |
|---|---|
| Small roof, under about 100 m² | $250–$400 |
| Average roof, about 100–200 m² | $400–$600 |
| Large roof, over about 200 m² | $550–$900 |
| Moss and lichen treatment added to the clean | $100–$250 |
A guide only, rounded from figures Auckland operators publish (checked October 2026); some sources don't say whether GST is included. Steep, two-storey or heavily grown roofs cost more. We confirm your price after seeing the roof.
How a roof clean runs
- We ask about the roof material and the age of the house, and look at photos or the roof from the ground.
- Pre-2000s and decramastic roofs are flagged for low-pressure methods only.
- Downpipes and drains are diverted or covered so wash water stays out of the stormwater; any tank inlet is disconnected.
- The crew plans safe access for the roof, then applies the cleaning solution at low pressure.
- Loosened growth is rinsed gently or left for the weather to clear, depending on the roof and what you want.
- Gutters are checked, and anything that needs a roofer is noted for you.
Questions people ask about roof cleaning
Why is roof cleaning so expensive?
Most of the cost is access and care rather than chemical. The crew has to plan safe access and fall protection for work at height, protect downpipes, drains and gardens so nothing reaches the stormwater, and take the time to clean at low pressure. Steep, two-storey or fragile roofs take longer. Even so, published Auckland prices for a clean are a small fraction of what re-roofing costs.
How much should I pay for roof cleaning?
For a typical single-storey North Shore home, published Auckland figures suggest roughly $250 to $600, rising to around $900 for large roofs, with a moss treatment adding $100 to $250 if it isn't included. Compare what each quote covers: a low-pressure method, run-off control, a gutter clear-out and any follow-up. A cheap quote that involves a blaster on an older roof is a warning sign.
What time of year is best to clean a roof?
Whenever you can get a dry, settled spell, because the cleaning solution needs a dry roof and Auckland Council says moss removers shouldn't go on when rain is forecast. NIWA notes Auckland's dry spells mostly come in summer, so late spring to autumn is often easiest, but mild winters mean a clear week can work any time. If a summer repaint is planned, treat a few months ahead.
Do you walk on the roof?
Sometimes the crew has to, and when they do it's planned. WorkSafe treats any work where someone could fall as work at height, with no minimum height, so access and fall protection are worked out for each roof before anyone goes up. Many roofs can be treated from a ladder or the edge. We won't promise more than that, and we'd never suggest you go up yourself.