Most roofs on the Tweed are not dirty in the way a car is dirty. They are damp for most of the year, salted from the coast, and slowly growing things. Understanding which of those three is causing the marks on yours decides whether the answer is a wash, a repair, or nothing at all.
The short version
- Bureau of Meteorology records put mean 9am relative humidity at Coolangatta between 61 and 72 per cent every month of the year.
- Salt does not rinse off the surfaces rain never reaches. The steel manufacturer asks for those areas to be hosed every six months, more often on the coast.
- The same manufacturer specifies soft cloths and mild detergent, and rules out abrasive scourers and steel wool.
- Organic growth on a roof is a symptom of moisture that is not draining or drying, so the cause is often shade, debris or a gutter, not the roof itself.
- Staining that comes back within months is usually a leak or a failed fixing, not dirt.
The climate a Tweed Heads roof lives in
Two numbers explain most of what happens on a roof in this part of the world, and both come from the Bureau of Meteorology station at Coolangatta, number 040717, which is the closest long record to Tweed Heads.
The first is rainfall: a mean of 1,535.1 mm a year, across an average of 108.5 days with at least a millimetre of rain. The second is humidity. Mean 9am relative humidity sits between 61 and 72 per cent in every single month of the year, peaking at 72 per cent in February and March. The 3pm figure never drops below 56 per cent.
That combination is unusual. Plenty of Australia gets more rain in a burst. Very little of it stays this damp between the bursts. A roof here does not get a chance to dry out properly for months at a time, and a surface that stays damp grows things.
Which is why growth is a symptom, not the problem
Moss, lichen and algae need moisture and shade. On a roof that drains and dries, they struggle. On a roof with a shaded southern face, overhanging branches, trapped debris in the valleys or a gutter that keeps the lower courses wet, they take hold.
This matters because it changes the job. If a roof is cleaned and the growth is back in a year, cleaning was never the answer. Something is keeping that section wet, and until the branches come back or the gutters clear properly, it will keep coming back.
Salt, and the surfaces rain never reaches
Everything within a few kilometres of the beach carries marine salt. Rain rinses the surfaces it hits and leaves the rest, and the rest is where corrosion starts.
The manufacturer of the coated steel used on most local roofs is direct about it. Its maintenance guidance asks that areas not regularly washed by rainwater be hosed down at least every six months, and "more frequently in coastal areas where marine salt spray is prevalent". The examples it lists include wall cladding under eaves and the underside of eave gutters.
So on a coastal roof, washing is not cosmetic maintenance. It is the manufacturer's own instruction for keeping the coating doing its job, and the areas that need it most are the ones nobody looks at.
What not to do to a roof
The temptation with a stained roof is to attack it. The manufacturer's own cleaning guidance goes the other way: washing should be done with a mild solution of pure soap or non abrasive dishwashing detergent in warm water, applied with "a sponge, soft cloth or soft bristle nylon brush (no abrasive scourers, steel wool etc)", then rinsed with fresh water immediately.
Anything harsher takes the coating with the stain. On a coastal roof, removing the coating is the one thing you cannot afford to do, because the coating is what stands between salt and steel.
The fixings, which is where roofs actually leak
A metal roof is held down by screws, and screws are the part of the roof exposed to weather at every single one of several hundred points. They back out over time and they corrode, and once a fixing has gone, that is where the leak starts.
This is worth knowing before booking a roof clean, because a roof that is leaking at the fixings does not need cleaning. It needs re-screwing, which replaces those screws across the sheets and starts from $1100. A wash will make it look better and change nothing about the water coming in.
How to tell the difference from the ground
Uniform darkening across a whole face, heavier on the shaded side, is growth. Streaks running down from a fixing line, or rust blooms at regular intervals, is a fixing problem. Staining on a ceiling below is neither, and means water is already inside.
Tiled roofs fail differently. Slipped or cracked tiles, and pointing that has given way at the ridge, let water in without any visible mark on the tile face. General roof repairs and maintenance start from $350 and include leak chasing on both tiled and metal roofs.
Timing it around the weather
The NSW SES puts storm season between September and April and reports more than 29,000 storm incidents in one recent season, with fallen trees and leaking roofs a large share of them. Bureau records make August and September the driest months of the year here.
That points at the same window as everything else on a roof. Late winter, before the storms, while the surface is as dry as it gets. A roof going into February with clear valleys, clear gutters and sound fixings is a roof that is not about to become an emergency.
Solar panels, while you are up there
Panels sit in the same humid, salty air as the roof and they are glass, so they hold film. A panel that is not clean is not producing what it was sized to produce. Solar panel cleaning runs at $15 per panel and is worth doing on the same visit as the roof and gutters rather than as a separate trip up a ladder.
Choosing someone to do it
Roof work is height work. The things worth asking about are insurance, working at heights training, and what happens if something is found up there that was not part of the quote.
First Choice Gutter Services is licensed and insured and holds working at heights certification, and works across Tweed Heads, Banora Point and Coolangatta and the rest of the coast from the Northern Rivers to the Gold Coast. The work happens where you cannot see it, so before and after photos of the job come back to you along with an explanation of what caused the problem. If something is missed, First Choice will come back.
If you are not sure whether your roof needs a clean, a repair or nothing, ask for a free quote and get it looked at first.