Cleaning a roof sounds simple, but the wrong method can do more harm than the dirt. High-pressure water can strip the coating from tiles, force water under laps and flashings, and on some older roofs release asbestos fibres. Strong chemicals running off the roof can kill garden plants and pollute streams. The right approach depends on what your roof is made of, how close you are to the sea and what is growing on it.
We clean and treat steel, iron, concrete tile and membrane roofs across Auckland, either as regular maintenance or as preparation before roof painting. Cleaning is also a chance to look closely at the roof, so we photograph anything that needs attention and tell you about it, without pushing work you do not need.
Pricing: every roof gets a free on-site measure and an itemised written quote, with a fixed price agreed before any work starts.
Paint worn through or rust showing once the roof is clean? Recoating is covered under roof painting.
Why roof cleaning matters
Moss and lichen hold moisture against the roof surface. On concrete tiles that speeds up surface erosion, and on steel it keeps the coating wet for long periods. Leaves and debris build up in valleys and behind skylights, damming water where it should flow freely. Near the coast, salt deposits in sheltered areas that rain does not reach, such as under eaves and around gutters, and that is where corrosion usually starts on steel roofs.
- Green or black growth on shaded roof planes and tiles
- Lichen patches that look like grey or orange spots
- Debris collecting in valleys, gutters and against chimneys or skylights
- Salt crust or dull, dirty areas under eaves on coastal homes
Washing steel roofs and your warranty
COLORSTEEL's warranty conditions depend on the environment category your house sits in. In milder environments rain washing is enough for the exposed roof, but sheltered areas that do not get rain-washed should be cleaned regularly. As the environment becomes more severe, the manual washing interval shortens, from yearly to every six months to every three months, and accessories in very severe sites need cleaning monthly. Skipping this washing can affect warranty claims.
For a steel roof we use a low-pressure wash with a soft brush and a cleaner that is safe for the coating, paying particular attention to unwashed areas, laps and fixings. If we find chalking, rust spots or failed fixings, we photograph them and tell you whether a repair, repaint or a COLORSTEEL longrun replacement would be the sensible next step.
How It Works
Moss treatment on tile roofs
Concrete tiles are porous, so moss and lichen root into the surface. Killing the growth first means it can be removed with gentle washing rather than aggressive blasting. Biocide treatments typically need time to work: Resene's Moss and Mould Killer, for example, is diluted and left for up to 48 hours before washing, and heavy growth may need a repeat application. Lichen can take longer than moss to release, and some residue is best left to weather away after treatment rather than being forced off.
While we are on a tile roof we check for cracked or slipped tiles and loose ridge capping. If there are more than a few, our tile roof repairs page explains how those are fixed.
Asbestos and older roofs
WorkSafe New Zealand prohibits the use of high-pressure water spray on asbestos-containing material. Its guidance defines high pressure as anything over 350 kPa, or 50 psi, and sets out infringement fees and court fines for breaches. Super Six and other fibre cement sheet, some cement tiles and some decramastic roofs laid before asbestos was phased out can contain it. WorkSafe recommends a soft wash or chemical wash instead.
If your roof could contain asbestos, we arrange testing before any cleaning starts and only use low-pressure methods. For roofs in poor condition, replacing them may be the safer long-term choice, and we can quote both.
Protecting drains, tanks and gardens
Auckland Council's guidance on pressure washing states that discharging washing waste into the stormwater system is illegal and that the operator is responsible for preventing it. Stormwater drains lead straight to streams and the harbour, so cleaning chemicals and moss debris must not go down them. We disconnect or block downpipes where needed, capture runoff, protect plants, and remove debris from the site. If you collect drinking water from your roof, we disconnect the tank supply before cleaning and tell you when it is safe to reconnect.
What affects the cost
Roof cleaning is quoted on the roof area and type. The amount of growth, the need for treatment and a return visit, roof pitch, height and access, runoff control, and whether you want gutters cleared at the same time all affect the price. Regular cleaning is cheaper than a heavy clean every few years, especially on coastal sites in suburbs such as Devonport, Takapuna, Howick and Whangaparāoa where salt builds up quickly.
Why Choose Cheeky's Roofers for Roof Washing
Method matched to the roof
Soft wash for steel and suspect roofs, treatment first for moss on tiles, never high pressure on asbestos.
Runoff kept out of drains
We control and capture washing waste in line with Auckland Council guidance.
Warranty-aware washing
On COLORSTEEL roofs we focus on the sheltered areas your warranty conditions call out.
Photos of what we find
You get a short photo summary of any issues, with no pressure to book further work.
Roof Washing FAQs
How often should I clean my roof?
It depends on the roof and exposure. COLORSTEEL sets manual washing intervals by environment category, from yearly to monthly for accessories in very severe coastal sites. Tile roofs under trees often need moss treatment every few years.
Is water blasting bad for my roof?
High pressure can damage coatings and force water under laps, and it is prohibited on asbestos-containing roofs. We use low-pressure methods suited to each roof type.
Does moss damage a roof?
Moss holds moisture against the surface, which speeds up erosion of tiles and keeps steel coatings wet. It also blocks gutters and valleys.
How long until the moss dies after treatment?
It depends on the product and the growth. Manufacturers such as Resene allow up to 48 hours for a full kill, heavy growth may need a second treatment, and lichen residue can take longer to weather away.
Is roof cleaning safe for my rainwater tank?
Only if the tank is disconnected first. We isolate the tank supply before cleaning and let you know when to reconnect.
Can you clean a roof before painting it?
Yes. Cleaning and treatment are the first stages of every roof painting job we do, and we can also clean on its own as maintenance.
Roof Washing by Area
Local roof washing information for your part of Auckland:
Related Roofing Services
Roof Washing Guides
- How to Remove Moss and Lichen From Your Roof (NZ Guide)
- How to Clean Your Gutters Safely (and How Often)
- Roof Painting Cost in NZ (and Is It Worth It?)
See the re-roofing cost guide or every service we offer.
Sources and further reading
- COLORSTEEL: warranty and maintenance (washing by environment)
- WorkSafe: High-pressure water blasting should not be used to clean roofing containing asbestos
- WorkSafe: Cleaning weathered asbestos-containing roofing and cladding
- WorkSafe: Check for asbestos before high-pressure spraying on roofs (safety alert)
- Auckland Council: Pressure washing and water blasting guidance
- Resene: Moss and Mould Killer data sheet