Drive through Killara, Pymble or Turramurra in late winter and you’ll see it on house after house: green film creeping up the south wall, black streaks under the eaves, moss cushioning the roof valleys. The Upper North Shore’s magnificent tree canopy creates a microclimate — more shade, higher humidity, slower drying — and biological growth loves every bit of it.
What’s actually growing on your house
Three different organisms, and they matter differently. Green film on walls is algae — mostly cosmetic, but it holds moisture against paint and render. Black streaks and spots are mould, which eats into paint binders and organic material and shortens repaint cycles. Moss and lichen on roofs and stonework are the serious ones: their root structures physically penetrate tile surfaces and mortar, and lichen in particular etches permanently into whatever it grows on. A lichen colony left for five years leaves a scar even after it’s removed.
Why bleach-and-hose doesn’t hold
Household bleach knocks the colour out of growth but rarely kills the root structure, so it’s back within months. And pressure-blasting growth off render or tiles removes the visible layer while leaving spores in every pore — plus it can strip paint and damage tile surfaces on the way through.
A proper soft wash uses purpose-made biocides at the right dilution, with enough dwell time to kill growth at the root, then rinses at low pressure. Done this way, a wash on a shaded North Shore home typically stays clean two to three times longer than a quick blast.
Prevention that actually works
After cleaning: trim vegetation back from walls where you can, keep gutters clear so overflow doesn’t feed wall growth, and consider a post-wash surface treatment on chronic south faces — it slows regrowth noticeably. Homes deep under canopy will always need a more regular schedule than a treeless block in the Eastern Suburbs; realistically, every 12–18 months keeps a Killara or St Ives home permanently presentable.
We soft-wash homes across Killara, Pymble, Turramurra, Gordon and the wider North Shore. If your south wall has gone green, request a fixed quote — we’ll identify what’s growing and treat it properly.
