Why walking your own roof is the wrong kind of brave
Because the savings do not survive contact with the surface. Wet tile sheds grip without warning, older fibre-cement and brittle sheets will not reliably hold a person, and the chemistry that actually kills moss is not the pressure washer from the hire shop. Proper roof cleaning is an access-and-chemistry job — which is why Schmick quotes it per job, priced firm in about 60 seconds.
Wet tile is not a walking surface
A roof looks walkable from the ground. That is the trap. Tiles carry a film of algae and lichen that stays slick long after the surface looks dry — and the moment you put water on the roof, which is the entire job, you are standing on the slickest version of it. Grip is not something you can check from the ladder. You discover where the film is by losing your footing on it, at height, with a hose in one hand.
Pitch compounds it. A roof that reads as gentle from the street feels very different underfoot, and the natural posture of a cleaning job — working downhill, dragging hose, watching the surface instead of your feet — is exactly the posture that goes wrong. None of this is drama. It is just what the surface is. Professionals treat wet tile as a no-walk zone not because they are timid, but because they have stood on it.
The roof is more fragile than you are
The other half of the problem is what your weight does on the way down. Tiles are brittle under point load — step in the middle of one instead of over the batten line and it cracks, quietly, under your shoe. Older fibre-cement sheeting is worse: it was never meant to carry a person between supports, and it does not give a warning before it gives way. Skylights and translucent sheeting have a habit of disguising themselves as roof.
So a DIY clean carries a double risk: the roof hurting you, and you hurting the roof. Crack three tiles finding your feet and the clean has already cost more than it saved — and a cracked tile does not announce itself on the day. It announces itself later, as a stain spreading across a ceiling, and by then finding which tile is a job in itself.
The hire-shop pressure washer is the wrong tool anyway
Suppose the footing goes perfectly. The standard DIY method still fails on chemistry. A pressure lance blasts the visible growth off the surface and leaves the organism alive underneath, so the roof greens up again within months. Along the way it can strip the surface coat off concrete tiles, scour pointing out of ridge capping, and drive water up under laps — damage you paid a hire fee to inflict.
Proper roof cleaning runs the other direction: low pressure, and a treatment that actually kills the moss and lichen so weather carries it away dead. That is the same gentle-washing logic the coating manufacturers themselves publish — we have written separately about what BlueScope's own bulletin asks of a Colorbond roof, and none of it involves a lance. The chemistry is the job. The pressure is mostly theatre.
What proper access actually looks like
A professional roof clean starts with a decision you never see: whether this roof gets walked at all. Much of a roof can be treated from the edge — roof ladders that spread load, anchor points and harnesses where standing is unavoidable, long-reach low-pressure applicators for the rest. Where a roof must be walked, the operator walks the batten lines on dry tile, not the spans on wet. Knowing which roofs are never walked is most of the skill.
The chemistry side is equally deliberate. Dilution is matched to the material and the growth, not guessed from a jug label. Gardens and downpipes are protected and rinsed, because the treatment that kills lichen is not kind to hydrangeas. And the job ends with photographs — before and after — because it is the one surface of your home you will otherwise never see.
The ledger, added up honestly
Here is the DIY side of the ledger: gear hire, chemicals, a full weekend, and the outcomes you carry alone — a cracked tile you cannot find, a stripped patch you can see from the street, growth back by autumn, and the fall risk you accepted for all of it. The professional side is a single line: a price for the whole job, done from proper access, with the right chemistry, photographed.
Roof cleaning is quoted per job because the variables — size, pitch, growth, access, material — are the whole job. Schmick's instant quote weighs them and returns a firm, bookable price in about 60 seconds, and it holds unless the place is materially different from what you told us. Get your number, set it against the weekend, and keep your feet on the ground.