Spray it, leave it, let the rain finish the job.
Roof moss treatment is a low-pressure chemical application: it kills moss, mould and lichen on contact, then Canterbury's weather breaks the dead growth down over the following months. No pressure on the roof, no cracked tiles, no water forced under laps. Published indicative pricing runs $345 to $450 for standard homes, and the gutters need attention afterwards, not before.
Is this your stream?
Green growth on the roof, especially shaded southern slopes and under overhanging trees. Treatment kills it at low pressure and the weather removes it over months. Preventive treatment on a two to three year cycle keeps it from re-establishing.
Cladding is soft washing, concrete is water blasting. And if the roof itself is failing, that is a roofer conversation, not a cleaning one.
What roof treatment costs in Christchurch
One franchise publishes indicative NZ pricing; the rest quote by roof size, pitch, access and growth load.
$345–$450
Published price indications, not fixed: $345 for 80 to 120m², $375 for 120 to 180m², and $400 to $450 for double-storey equivalents. Size, pitch and growth load move the final quote.
$300–$1,000
Published NZ guides put professional roof cleaning and treatment at $300 to $1,000, with heavy growth, steep pitches and difficult access at the top end. Community-reported Christchurch quotes sit mid-range, around $480 for a 10-year-old tile roof.
~$250+GST
Added to a house soft wash, roof treatment typically prices around $250+GST, and published three-item bundles (house, roof, driveway) start from about $590+GST for homes up to 150m². Bundling beats a second callout.
Christchurch roof treatment providers, compared
Published-price franchises, roofers and treatment specialists. Hover a row for the detail that matters.
Choose by situation
Metro publishes indicative treatment pricing by roof size ($345 to $450 for standard homes). Use it to sanity-check every other quote you collect.
Arthur's Roof has worked Canterbury roofs since 1979 and treats moss as part of roof health, alongside gutters and spouting. Christchurch Roof Restorations bundles treatment with painting and repairs at fixed upfront pricing.
The Washdown King's drone spraying treats roofs that should not be walked. Decramastic and brittle tiles crack underfoot; chemistry applied from the air does not.
TLC Softwash offers a workmanship guarantee on moss, mould and lichen treatments, and Chemwash brings a 40-plus-year spray-and-leave system. Documented guarantees suit property managers.
Common mistakes
Water blasting a roof to remove moss: pressure strips protective coatings, cracks tiles and forces water under laps, and industry practice warns against it for leak liability. Treatment is a chemical spray-and-leave job; the rain does the rinsing over weeks.
Expecting instant results: spray-and-leave treatments kill growth on contact but the dead moss and lichen weather off over months. Judging the job the next morning misunderstands the method.
Treating the roof but leaving the gutters full: dead moss washes into the spouting. Book a gutter clean a few weeks after treatment, or bundle one in, or the first nor'wester rain dumps it all into your downpipes.
Walking a fragile roof to save money: old decramastic tiles and brittle roofing crack underfoot, and a wet roof is dangerous. Drone spraying (The Washdown King) and boom application exist for exactly these roofs.
Treating without fixing the cause: overhanging branches and shaded southern slopes regrow fastest. Trim the canopy where you can, or budget for treatment on a two to three year cycle.
Comparing a treatment quote against a roof clean quote: treatment kills and weathers off over months; cleaning removes immediately at higher cost and risk. Know which one is being quoted before comparing numbers.
FAQ
How much does roof treatment cost in Christchurch?
Metro publishes NZ price indications: $345 for an 80 to 120m² roof, $375 for 120 to 180m², and $400 to $450 for double-storey equivalents. NZ-wide published averages run $300 to $1,000 depending on size, pitch, access and growth load. As an add-on to a house wash, roof treatment typically prices around $250+GST.
How does spray-and-leave treatment work?
A biocide is sprayed at low pressure, kills moss, mould and lichen on contact, then rain and weather break down the dead growth over the following months. No pressure on the roof, no walking fragile tiles. Community reports describe Chemwash-style treatments carrying a 12-month service warranty with free re-treatment if growth returns early.
Treatment or water blasting for a mossy roof?
Treatment. Water blasting strips protective coatings, cracks tiles and forces water under laps, and operators warn about leak liability. The only pressure that belongs near a roof is the low-pressure application of the treatment itself.
How long before the roof looks clean?
The treatment kills growth within days, but dead moss and lichen take weeks to months to weather off with rain. Canterbury's mix of nor'wester rain and dry spells shifts that timeline. If you need the roof visually clean this week, that is a roof clean, a different and more invasive job.
What should I ask before booking?
State roof material, pitch, storeys and access, and how heavy the growth is. Ask whether the quote is treatment or clean-and-treat, what product is used, whether gutters are cleaned afterwards or bundled, how the operator accesses steep or fragile roofs, and what the warranty or re-treatment policy is.
Published indications run $345 to $450 for standard roofs (Metro), around $250+GST as a house-wash add-on. Arthur's Roof for a roofer's full picture, Christchurch Roof Restorations for treatment inside a wider restoration, Chemwash and TLC Softwash for guaranteed spray-and-leave systems, The Washdown King for drone application on fragile roofs. Never water blast a roof, expect months not days for full visual results, and book the gutter clean for after the treatment, not before.