The North Shore has the opposite problem to the coast. Very little salt, and instead deep shade, mature canopy, and surfaces that never properly dry out.
That changes what goes wrong and what the right method is.
The canopy problem
Turramurra, Wahroonga, Pymble, St Ives, Killara, Roseville, Castlecrag, Northbridge and Hunters Hill share a characteristic: large established trees, often on the southern side, over houses on generous blocks.
Three consequences.
Permanent shade. South elevations in these suburbs may get no direct sun for months. Moss, mould and lichen establish and stay — why North Shore homes go green.
Continuous leaf drop. Not seasonal. Gutters fill year-round, valleys block, and paths accumulate a damp organic layer.
Tannin staining. Leaf litter sitting on concrete and sandstone in the wet leaches tannin and leaves brown staining. It is not dirt and it does not pressure off — it needs the right chemistry.
Specific suburbs have their own character: Castlecrag and Northbridge are built into bushland, Greenwich and Longueville have camphor laurels and old stormwater, and Hunters Hill is colonial sandstone with lime mortar.
Lichen
The signature North Shore problem.
Lichen thrives in exactly these conditions — damp, shaded, undisturbed — and it is the growth that does not respond to pressure. It anchors into the surface, so blasting it removes the surface rather than the organism. On roof tiles that means stripping the factory coating and creating a more porous tile that grows lichen faster.
It needs chemistry and patience. The full explanation.
Sandstone
Sandstone retaining walls, steps, paths and foundations are everywhere on the lower North Shore, and in the damp they go black with biological growth.
Two rules. No high pressure, which erodes the surface and makes it more absorbent and faster to re-blacken — here. And no acid, which dissolves the carbonate cement holding the grains together.
Why it blackens in the first place is covered in why Sydney sandstone turns black, and the sealing question in sandstone sealer.
Heritage
Large parts of Hunters Hill, Lane Cove, Willoughby, Ku-ring-gai and Mosman sit in conservation areas, and a good deal of the housing is Federation or interwar.
That brings constraints: lime mortar that modern cement pointing damages, pre-1970 paint that may contain lead, and tuckpointing that abrasive cleaning destroys. See heritage listings and conservation areas and lead paint on pre-1970 homes.
Older brickwork in a damp, shaded position is also prone to fretting, where washing makes things worse rather than better — here.
Gutters and the damp consequences
Gutter cleaning on the North Shore needs doing three times a year on a heavily treed block, not twice.
The consequences of not doing it are worse here too. Overflowing gutters on a house that is already shaded and damp produce interior mould quickly — see mould on a bathroom ceiling and blocked downpipes.
Roof-space ventilation matters more in these conditions as well — whirlybirds and roof vents.
Possums
More common here than almost anywhere in Sydney, because the canopy runs right up to the rooflines. They are protected, exclusion is the only legal approach, and the cleanup afterwards is its own job — possums in the roof.
Cutting back branches within two metres of the roof solves the possums and halves the gutter load at the same time.
What actually takes pressure
Driveways, paths, pavers and sound concrete. Everything else on a North Shore property — roof, render, sandstone, timber, heritage brick — is a soft wash or a specialist job.
Given how much of the housing stock here is old, shaded and built from soft materials, this is a region where the wrong contractor does expensive damage.
Frequency
House wash every 18 months to two years on a shaded block, sooner on a south elevation under canopy. Gutters three times a year. Paths and driveways annually, mainly for slip resistance.
The regional overview is in the North Shore exterior cleaning guide, and the Mosman-specific version in soft washing Mosman Federation homes.
For a quote, see house washing or gutter cleaning.
