Lichen, Moss and Mould on Karori and Northland Roofs

2026-10-26 · 4 min read

Karori, Northland, Brooklyn and Wadestown sit high, catch plenty of cloud and have lots of mature trees. Roofs in these suburbs often carry a mix of green moss, crusty grey or orange lichen and black mould. They look similar from the street, but they grow differently and cause slightly different problems.

For most roofs, a gentle moss and lichen treatment applied by a roofer is the safest option. It kills growth at the root and lets the weather wash it away gradually, without blasting coatings or forcing water under laps and tiles.

Telling them apart

Moss is soft and green, holds water like a sponge and builds up in valleys and on the shady side
Lichen is flat and crusty, grips tightly and can etch coatings over time
Mould and algae show as dark streaks and stains, often below ridges and on north facing slopes

Why water blasting is risky

High pressure water can strip paint from iron, wear the surface off concrete tiles and drive water under flashings. On older roofs it can crack brittle tiles or loosen fixings. A treatment takes longer to show results but is far kinder to the roof.

What to expect after treatment

Moss usually browns within a few weeks and washes off over the following months. Lichen takes longer and may leave a faint mark. A follow up treatment every couple of years keeps regrowth down, especially under trees.

Reducing regrowth

Trimming overhanging branches lets more sun and wind reach the roof, and keeping spouting clear removes the damp debris that moss loves. On sheltered sections, these simple steps make a noticeable difference.