Controlled pressure, not full blast
Pressure washing a roof has a bad name because of the way some contractors do it: lance on full power, blasting away at the tiles. Done that way it strips the tile surface and forces water where it shouldn't go. Done properly it's the fastest and most effective way to clean a sound roof, and it's our standard method. We clean with a rotary surface cleaning disc rather than an open lance, and the pressure is governed down to the gentlest setting that shifts the moss and grime. We're not hammering the tile; we want to see the dirt and moss go at the least pressure we can use, and we can control that.
Angled down the pitch, never under the tiles
Direction matters as much as pressure. A roof is built to shed water running downward, so that's the only way we work: the washer is always angled down the pitch, never upward or across the laps, so nothing is driven under a tile or into the roof space. Some grit comes off with the moss and that's normal; what you don't get is water pushed where the roof can't handle it. We've cleaned roofs this way on houses across Teesside for years, on forty-year-old tiles that take a careful wash perfectly well.
Hot water for stubborn growth
Where growth is well established we can add heat to the job. Water runs from the pressure washer through our heat box and out through the disc as hot water, flowing across the roof as we work. Heat lifts greasy soiling and heavy biological growth that cold water alone takes longer on, so the tile comes up clean in a single visit. It's an instant result: the roof looks clean the day we leave, not months later.
When we scrape and treat instead
There's one condition for pressure washing a roof: it needs to be in good order. On a very old or fragile roof we take the gentlest route instead, scraping the moss off by hand, tile by tile, then applying a biocide treatment. That method is slower to show results because the biocide keeps killing the remaining growth over the following months, but it puts no working pressure on the tiles at all. We'll tell you honestly which method your roof suits when we come to quote.
The biocide finish, guaranteed for 12 months
Whichever way the roof is cleaned, the job isn't finished until it's treated. We apply a biocide treatment after every clean, which kills the remaining spores at the root rather than just removing what you can see. It keeps working long after we've left, and we stand behind it: no regrowth, guaranteed for 12 months.