Kill it with chemistry. Never with pressure.
Wellington's damp shade and wind-borne spores grow moss and lichen on every roof type the city has, from Mount Victoria decramastic to Karori concrete tile. Treatment kills the growth and the weather carries it away over months; a soft wash cleans it off on the day. The one method no Wellington roof should ever meet is a water blaster.
Is this your stream?
Green moss cushions, black or pale lichen patches, or a roofline that looks older than it is. Also the pre-purchase discovery: a builder's report flagging growth that will shorten the roof's life if ignored.
Grimy walls and salt film are soft wash. Slippery paths and driveways are water blasting. Leaks, cracked tiles and rusted fixings are a roofer, and two of the providers below are exactly that.
What roof treatment costs in Wellington
Nobody publishes treatment rates locally. The inspection is the quote, so structure the comparison.
Quote after inspection
Treatment is priced per roof after assessing material, pitch, access and growth. Expect a fixed price for the treatment, with washing, repairs and gutter work quoted as separate lines.
$600–$1,000+ bundle
Metro Water Blasting's published Wellington guide prices full exterior packages including roof treatment, house wash, gutters and driveway at $600 to $1,000+. If everything is due, the bundle is the cheapest way to get the roof done.
Pitch + access + growth
Steep pitches, three-storey hill sections, heavy established lichen and fragile decramastic all move the number up. An open low-pitch roof with light moss is the cheap end.
Wellington roof treatment providers, compared
Roofer-led specialists first, then treatment-led exterior washers. Hover a row for the detail that matters.
Choose by situation
Moss Off Roofing Solutions are Roofing Association of NZ members, and Above Focus Roofing treats moss inside a full roofing practice. When treatment might reveal cracked tiles or failing fixings, a roofer spots it and can fix it.
Prowash Wellington assesses each roof and chooses soft wash or moss treatment by surface and condition, with biodegradable products. Maximum Wash builds a customised treatment plan per roof type. Both suit mixed or fragile roofing stock.
Metro's published Wellington packages bundle roof treatment with house wash, gutters and driveway at $600 to $1,000+. Manta Wash covers roof soft wash and treatment alongside house washing. One crew, one callout.
Treatment works over months; a soft wash works on the day. If the roof must look clean for a deadline, say so when quoting: you are buying a wash with a treatment chaser, not a treatment alone.
Common mistakes
Water blasting the roof: high pressure strips the coating off concrete tiles, tears the stone chips off decramastic, and forces water under laps and flashings. Wellington roofs are cleaned with soft wash or treated chemically, never blasted. Any operator suggesting otherwise should be walked off the property.
Expecting the roof to look clean the day after treatment: moss and lichen treatments kill the growth, then rain and wind remove the dead material over months. That is normal and correct. If you need instant appearance for a sale, that is a soft wash, quoted differently.
Treating without fixing the cause: overhanging branches and blocked gutters keep the roof damp and the spores coming. Trim what shades the roof and clear the spouting first, or the treatment interval shortens dramatically.
Walking a fragile roof to save money: decramastic and older concrete tiles crack under foot traffic, and every cracked tile is a future leak. Ask exactly how the roof will be accessed and whether the crew works from the gutter line, a platform or the roof itself.
Ignoring the tank water: if the house collects rainwater off the roof, treatment chemicals go straight into the tank. Disconnect or divert the downpipes before treatment and flush before reconnecting. Every operator should raise this; if yours does not, raise it yourself.
Assuming lichen is cosmetic: lichen roots into tile coatings and holds moisture against the surface, accelerating breakdown and rust on metal roofs. On a Wellington roof facing the harbour weather, untreated lichen is a maintenance debt with interest.
FAQ
How much does roof treatment cost in Wellington?
No Wellington specialist publishes treatment rates: quotes follow an inspection of roof type, pitch, access and growth level. The structure to expect is a per-roof fixed price for the treatment itself, with washing, repairs and gutter work as separate lines. Metro Water Blasting includes roof treatment in its published Wellington exterior packages at $600 to $1,000+ bundled with house wash, gutters and driveway, which is the only public number in the market.
Treatment or roof wash: which do I need?
If the roof is structurally sound but green or black with growth, a chemical treatment kills it and the weather removes the debris over the following months. If you need the roof to look clean now (sale, photos, body corporate deadline), a soft wash removes growth on the day. Prowash Wellington assesses and recommends per roof. Many roofs get both: wash now, treatment to keep it dead.
How long does a treatment last?
Typically years rather than months, depending on shade, nearby trees and which way the roof faces. South-facing and tree-shaded Wellington roofs regrow fastest. Operators will give an expected interval per roof; treat anything shorter than two years on an open roof as a prompt to ask why.
Is roof treatment safe for decramastic and old tiles?
Chemical treatment and soft washing are the safe methods for decramastic, concrete tile and Coloursteel. High-pressure blasting is the dangerous one: it strips stone chips and coatings. Moss Off Roofing's point that its people are roofers, not just roof cleaners, matters here: the person treating the roof should know what breaking it looks like.
What should I ask before booking?
State the roof material, age, pitch and access, whether you are on tank water, and whether the goal is appearance now or long-term control. Ask how the roof will be accessed, whether the quote includes a wash or treatment only, what happens to gutters and downpipes during treatment, and what regrowth warranty applies.
Treatment kills growth over months; a soft wash cleans on the day; pressure never touches the roof. Moss Off Roofing or Above Focus when you want roofers making the call, Prowash or Maximum Wash for a method matched to your roof type, Metro or Manta to bundle the roof with the rest of the exterior. Declare tank water, ask about access and regrowth warranty, and get the quote in writing after an actual inspection.