A couple in Wigram rang me in October 2024 because one painter had told them their 2008 roof needed a full repaint, and a second had said it needed nothing but a wash. Same roof, one week apart, quotes of NZ$7,800 and NZ$650. The Colorsteel was sound, the chalk test on the north face came back with a light dusting, and the south face had a carpet of lichen 3 mm thick along the laps. The honest answer was in between: wash it now, treat the lichen, replace about forty rusted screws, and plan the repaint for three or four years out. Nobody had told them that because nobody had a schedule in their head, only a job to sell.
Why Canterbury roofs age differently
Christchurch has some of the highest summer UV readings of any New Zealand city, low humidity, and a nor’wester that arrives hot, dry and dusty. That combination chalks paint fast but grows little moss on exposed faces. Winter brings frost, occasional snow and long damp spells on south-facing pitches that never dry out between June and August. A Canterbury roof has two separate problems on two faces: chalk and UV breakdown on the north and west, lichen and standing moisture on the south and east. A single maintenance interval does not fit both.
Washing: every two to three years
A soft wash with a moss and mould treatment, left twenty minutes and rinsed at low pressure, is enough on most Christchurch roofs every two to three years. Coastal suburbs, New Brighton, Redcliffs and Sumner, should be on the shorter end because salt sits on the steel and accelerates corrosion at every cut edge. Roofs under trees, Ilam and parts of Avonhead in particular, also want the shorter cycle because leaf litter holds water against the sheet. At 2026 prices a wash on a 160 to 200 square metre roof is NZ$450 to NZ$900. The number to watch is pressure: over 20 MPa on an older painted roof strips coating, and I have inspected more than one roof where the wash did more harm than the lichen.
Inspecting: every spring, from the ground and then from a ladder
Every October, after the last frost, walk around the house with binoculars: lifted ridge caps, screws standing proud, cracked sealant at vent pipes, rust bleed at sheet bottoms, spouting pulling away from the fascia. Then get a ladder to the eave and look along the laps at eye level. A proper inspection by a licensed building practitioner (roofing) runs NZ$250 to NZ$450 and is worth doing every three to five years, or after any event with gusts over 120 km/h.
The things I find most often on Christchurch inspections are quake-era chimney patches and screws backed out under thermal cycling. Forty loose screws on a 1990s roof is normal. Two hundred is a fixing problem.
Repainting: twelve to fifteen years, if the wash cycle was kept
A factory-finished Colorsteel roof in Canterbury generally reaches the repaint point at fifteen to twenty years. A roof that has already been repainted once will need it again in ten to fifteen, because site-applied acrylics rarely match a factory bake. The trigger is not age but the chalk test: press black tape on a clean dry north-facing sheet and peel it. Light dusting, wait. A solid white band, repaint within two summers before the primer layer starts to go. If bare Zincalume is showing at the laps, the job has already grown; that needs a rust-converting primer at those points before anything else.
A two-coat acrylic repaint over a washed and spot-primed 180 square metre roof is NZ$5,500 to NZ$9,500 in Christchurch. Membership of a trade body such as Master Painters New Zealand is a reasonable starting filter when reading quotes, though it is the specification, the dry-film thickness and the primer that decide whether the job lasts.
One sequencing point: if the weatherboards or exterior render are due as well, do the roof first. Overspray and wash-down run downhill, and there is a walkthrough of how to order a roof and walls repaint that applies as well in Wigram as it does in Hamilton.
Putting it on a calendar
- Every October: ground and ladder inspection, clear the spouting, note anything that has moved.
- Every two to three years: soft wash and lichen treatment; sooner on the coast or under trees.
- Every three to five years: paid inspection, screw replacement, sealant renewal at penetrations.
- Every twelve to fifteen years after the first repaint: the chalk test decides the repaint, not the calendar.
The Wigram couple washed the roof that November for NZ$720 and replaced the screws. The repaint is pencilled in for 2028. Three more years out of a roof that one quote wanted to paint immediately is not a small saving, and painting over 3 mm of lichen would have failed inside five years anyway.
Frequently asked questions
How often should a Christchurch roof be washed? Every two to three years on most roofs, and every two years in coastal suburbs or under trees. Use a moss and mould treatment and rinse under 20 MPa so the coating is not damaged.
When does a Colorsteel roof in Canterbury need repainting? Usually at fifteen to twenty years from new, or ten to fifteen after a first repaint. The black tape chalk test on a north-facing sheet is the trigger, not the age.
What does a roof inspection cost in Christchurch? A ladder and roof-space inspection by a licensed building practitioner is NZ$250 to NZ$450. Do it every three to five years and after any wind event over 120 km/h.