Cleaning a concrete tile roof

If your concrete tile roof is looking grubby or is covered in lichen or moss, it might be time to think about getting it cleaned. While most people get their roofs cleaned simply for aesthetic reasons, keeping them in tip-top shape can occasionally have other, more practical benefits.

"A concrete tile roof absorbs more moisture as it gets older," says Paul Koutroubas from Action Roofing. "If there's too much lichen or if you have a lot of overhanging trees, the debris can get between your tiles and, in extreme cases, it can divert water into your roof."

To clean a concrete tile roof, roof-cleaning companies generally use a commercial Gerni, which is a petrol-driven device that blasts water out at high pressure. Cleaning a terracotta roof requires an additional step – the roof first needs to be sterilised with a chemical that kills off any fungus.

Roof-cleaning companies will generally clean your gutters too, removing leaves from them and then high-pressure cleaning them. According to Paul, roof cleaning should be done every 15 to 20 years. "But some people like to keep right on top of everything, so they do it every 10 years or so," he says.

To DIY or not

Though many people attempt it, Paul doesn't recommend cleaning your concrete tile roof yourself, as it's a specialised skill that requires particular equipment. "I've heard of people attempting roof cleaning with domestic Gernis, but they're not powerful enough," he says. "I've even seen people attempt it with a brush, sitting on the roof. You don't get too far doing it that way."

Besides being ill-equipped for the job, home owners are often not aware of the dangers of cleaning a concrete tile roof. "It's very dangerous," says Paul. "You're on a tiled roof, maybe one or two storeys up, and blasting water. Safety is important; we use harnesses and so forth. It's not just throwing water over an area; you've got to clean every inch of that tile, and there are a lot of tiles on a roof!"