By Tom, TMF Exterior Cleaning · 30 September 2026

Thick moss on a roof is one of the most common things homeowners ask us about. It's tempting to think a pressure washer will sort it out in an afternoon — but there isn't one right way to clean every roof, and high pressure is rarely it.

Why high-pressure washing a roof can cause problems

It erodes the tile surface. Concrete tiles have a surface layer that sheds water. High pressure can strip it away, leaving the tile more porous — which means moss comes back faster.
It forces water under the tiles. Roof tiles overlap to shed rain running down the roof. A jet aimed up or across the tiles can drive water underneath, onto the felt and battens.
It can crack or dislodge tiles. Older and clay tiles in particular can be brittle.
It's messy. Moss and slurry get sprayed across walls, windows, cars and gardens.

The right approach for your roof

We look at the roof first and choose a method to suit it. Thick moss on older or more fragile tiles is usually best taken off by hand, scraping and brushing each row. Many roofs suit a low-pressure roof wash, which lifts moss and grime without the force that damages tiles or drives water under the laps. Often the answer is a mix of both. Once the bulk of the moss is off, a biocide treatment is applied to kill the remaining spores and lichen. This keeps working for weeks after the visit, so the roof continues to improve and regrowth is slowed.

Finally, the gutters and downpipes are cleared of everything that has come down, and the ground is tidied up.

A chance to check your roof

Once the moss is gone, it's much easier to see the actual condition of the tiles. It's common to find the odd cracked or slipped tile that had been hidden — as one of our customers found. Small repairs like that can often be done while we're up there, before they lead to leaks.

How long does a clean roof stay clean?

That depends mostly on shade, nearby trees and which way the roof faces. North-facing slopes under trees will always grow moss faster than a sunny, open roof. After a thorough clean and treatment, most roofs stay clear for several years.

If your roof is starting to turn green, take a look at our roof cleaning and moss removal service, or send us a photo on WhatsApp for a quick quote.

Related services

Roof Cleaning & Moss Removal

Moss and lichen removed by hand or with a low-pressure roof wash — whichever suits your roof — then treated to slow regrowth.

Learn more

Gutter Cleaning & Repairs

Gutters cleared with a high-power vacuum and by hand, downpipes flushed, leaking gutters replaced and the outside washed back to white.