Why Newcastle roofs get grubby
Humid and often wet
Newcastle has a humid subtropical climate, with afternoon humidity at Nobbys averaging 67% and 92.2 rain days a year. Inland suburbs get more rain still: the university station, 8.5 km from the CBD, averages 1,111.2 mm against 1,034.5 mm on the coast. Shaded slopes in those conditions stay damp, and that's where moss and lichen take hold.
Terracotta grows it more readily
Monier says moss and lichen grow more often on terracotta, especially unglazed terracotta, than on concrete tiles, but only on the surface. It doesn't damage the tile itself. It can, though, hold water and block the gaps where tiles overlap, and it sheds into gutters.
Salt on the coast
Near Nobbys, Bar Beach, Merewether and Stockton, salt settles on roofs and in the places rain doesn't wash. BlueScope's October 2026 bulletin says those unwashed areas should be cleaned every three months in coastal areas with salt spray.
How to clean each kind of roof
| Roof | Do | Don't | |
|---|---|---|---|
| Terracotta or concrete tiles | A professional roof cleaner, as Monier recommends, using a gentle low-pressure method | Pressure wash, which Monier says risks damaging the tiles | |
| Colorbond or Zincalume | Fresh water and a soft brush or mop on unwashed areas | Abrasive or solvent cleaners like turps or thinners, or hard bore water | |
| Polycarbonate patio roofing | Warm soapy water and a soft sponge | A water blaster, which Laserlite says strips the UV layer | |
| Old fibre cement sheeting | Leave it alone and get it tested | Any pressure cleaning, which is illegal on asbestos in every state |
Pre-1990 sheeting could be asbestos
NSW says a house built before 1990 probably has asbestos-containing materials. ASSEA says pressure cleaning asbestos roofs has caused contamination costing hundreds of thousands of dollars to fix, with fibres spreading to neighbours' yards, footpaths and stormwater. If your roof is grey corrugated or flat sheeting and you're not sure what it is, don't clean it, and see is my roof asbestos?
Cleaning on its own, or before a coating?
A clean on its own is worth doing when the roof is sound and just dirty or mossy. If tiles are cracked or the ridge mortar is breaking up, clean as part of a restoration so the roofer can fix those at the same visit. See roof restoration in Newcastle. For moss specifically, our moss removal page goes further.
Ask a Newcastle roof cleaner
- Do you soft wash or pressure wash, and why for my roof?
- What treatment do you use on moss and lichen, and is it safe for my gutters and garden?
- Have you checked my roof isn't asbestos cement?
- Will you clear the gutters and downpipes of what comes off the roof?
- Will you tell me about cracked tiles or loose ridge caps you find?
Where we'd start
We'd only clean a tiled roof with a soft wash and moss treatment, never a blaster, and we'd book it for a dry spell outside the wet months. Near the beach, we'd hose the eaves and gutter undersides every few months ourselves from the ground. Anything that might be asbestos, we'd leave untouched until it's tested. The national roof cleaning page explains the methods, and the Newcastle page covers the local climate.
Want a roofer to take a look?
Tell us the job and your postcode. We match it with a Find My Roofer certified roofer who specialises in that kind of work, and they call you to quote. Your number goes to them alone.