How to Remove Moss From Roof Tiles (And Keep It Off)

Moss on roof tiles is one of those problems that starts small and becomes expensive. A thin green film turns into thick clumps over two or three years, and by the time you decide to deal with it, there's a real weight of wet vegetation sitting on your roof. Here's what actually works for getting rid of it, what doesn't, and how to stop it growing back.

Why Moss Grows on Roofs

Moss needs two things: moisture and a rough surface. Roof tiles give it both. Concrete tiles are porous. Clay tiles develop micro-cracks over decades of thermal expansion. Both collect enough moisture from rain, dew, and condensation to support moss growth year-round.

North-facing roofs get less direct sunlight and stay damp longer. Roofs shaded by trees or neighbouring buildings are worse again. If your roof faces north and sits under a canopy of mature trees, you'll see moss buildup faster than a south-facing roof in an open position.

The Methods That Work

Manual scraping plus biocide

This is the method we use for roof cleaning jobs across Northamptonshire, and it's what most reputable companies use too. The process has two parts.

First, the bulk moss is scraped or brushed off the tile surface by hand. This is slow work, but it's controlled. You can see what you're doing, you can feel whether a tile is loose before you put pressure on it, and you avoid the problems that come with blasting water at a roof.

Second, a biocide solution is applied across the entire roof. This is a professional-grade fungicidal wash that soaks into the tile pores and kills the remaining moss spores, algae, and lichen roots that you can't see from the surface. Without this step, the moss comes back within a few months because the root system is still alive inside the tile.

With the biocide, you get three to five years before regrowth becomes visible again. The exact duration depends on the roof's orientation and how much shade it gets.

Soft wash

Soft washing uses low-pressure water mixed with a cleaning solution to break down moss and algae without the force of a pressure washer. It's gentler than pressure washing and more effective than scraping alone for roofs with heavy lichen buildup. Some companies use this as the primary method, others use it as a finishing step after manual removal.

The Method That Causes Damage

Pressure washing

Pressure washing a roof will get the moss off. It will also strip the surface layer from concrete tiles, making them more porous and more prone to future moss growth. The high-pressure water gets forced under tile overlaps and into the felt beneath. On older roofs, it can crack tiles that are already weakened by frost damage.

We've cleaned roofs where the previous owner had them pressure washed a year earlier. The tiles were rougher, more porous, and the moss had already come back thicker than before. The tile surface had lost its factory coating, which is there specifically to slow water absorption.

Some roofing companies still offer pressure washing because it's fast. Fast doesn't mean good when it comes to roof tiles.

Can You Do It Yourself?

For a single-storey extension or a garage roof, DIY is realistic if you're comfortable on a ladder. You can buy moss scraping tools and biocide concentrate from builders' merchants. The biocide (sold under brand names like Algon or Pro-Kleen) costs £20 to £40 for enough to cover an average garage roof. Apply it with a garden sprayer on a dry day and leave it to work.

For a two-storey house roof, DIY becomes a safety problem. You need to reach the ridge line, you need stable footing on the tiles, and you need both hands free to work. Professional roof cleaning teams use tower scaffolding, cherry pickers, or harness systems for exactly this reason. Falls from domestic roofs account for a significant number of A&E admissions each year in the UK.

There's also the question of thoroughness. From a ladder, you can only reach the first few rows of tiles above the gutter line. The ridge, valleys, and centre sections of the roof stay untouched. A partial clean looks odd and leaves the worst-affected areas still doing damage.

How to Slow Down Regrowth

After a professional biocide treatment, moss growth is suppressed for several years. Beyond that, there are a few things that affect how quickly it comes back:

• Trim overhanging branches that shade the roof and drop organic debris onto tiles
• Keep gutters clear so water drains off the roof instead of backing up
• Check ridge mortar periodically; gaps in ridge pointing trap moisture that feeds moss

Zinc or copper strips fitted along the ridge line are sometimes suggested as a long-term moss deterrent. The theory is that rainwater washes trace metals down the roof surface and inhibits growth. Results vary. Some homeowners report good results, others see no difference. They're not a substitute for a proper clean and biocide treatment, but they might extend the time between cleans.

When to Call a Professional

If the moss on your roof is thick enough to grab in clumps, if you can see it from the pavement, or if your gutters are clogging with moss debris, it's past the point where a garden spray will sort it. You need someone with the right access equipment to clear the bulk, treat the surface, and check the tiles underneath for damage.

We cover Northampton, Kettering, Wellingborough, and the rest of Northamptonshire. If you want a quote, get in touch and we'll come and look at the roof before giving you a price.