Moss on Your Roof: Should You Remove It?

Why moss grows on roofs

Moss thrives in damp, shaded places, and a roof in the North East gives it plenty of both. North-facing roof slopes, roofs shaded by trees and roofs that stay wet after rain are usually the worst affected.

Concrete tiles, with their slightly rough surface, give moss something to grip on to. Once a small patch takes hold, spores spread easily across the rest of the roof, and those small green tufts can turn into thick cushions over a few years.

Roofs that are shaded or stay damp often see moss return year after year simply because of the conditions around them.

Is moss actually a problem?

A light covering is mainly a matter of looks, but heavier growth can cause real problems:
✓ It holds water. Moss acts like a sponge, keeping your tiles damp for longer, and in freezing weather that trapped water can expand and crack tiles
✓ It can lift tiles. As moss builds up between and under the edges of tiles, it can push them apart and allow rain to be driven underneath
✓ It blocks gutters. Clumps of moss wash or fall down into the gutters and downpipes, which is one of the most common reasons gutters overflow

So while a few specks are nothing to worry about, a roof with thick moss is usually worth dealing with before it starts causing damage.

Why we don't pressure wash roofs

Plenty of tradesmen pressure wash roofs, and we do own pressure washing gear, but it isn't the method we prefer for roofs. We'd rather take the moss off by hand and follow up with a biocide treatment, which clears the thick growth and keeps working on what's left long after we've gone.

Working by hand also keeps things tidy, with the moss collected up as we go. It's simply the way we prefer to do it.

How we remove moss safely

Our preferred approach is a simple two-step process. First, the bulk of the moss is removed by hand, carefully scraping it off the tiles. This takes a bit longer, but it's a careful, thorough way to get the bulk of the moss off.

Next, we apply a biocide treatment across the roof. This kills the remaining moss, algae and lichen, including the roots and spores that you can't see and that hand removal alone would leave behind.

We also make sure debris is cleared up afterwards. Because so much moss ends up in the gutters, it makes sense to have your gutters cleared at the same time.

What happens after the biocide treatment

It is worth knowing what to expect, because the results carry on after we leave. The biocide continues working after it has been applied, and any remaining growth and staining gradually weathers off over the following weeks and months, helped along by the rain.

So your roof will look much cleaner straight after the moss has been removed, and it will keep improving over time rather than looking its best on day one. The treatment also helps slow down new growth.

How often does a roof need cleaning?

There is no fixed rule. It depends on how shaded your roof is, which way it faces and how much tree cover there is nearby. A sunny, open roof may stay clear for a long time, while a shaded roof under trees will usually see moss come back sooner.

Keeping an eye on your roof from the ground each year, and dealing with moss before it gets thick, is the best way to stay on top of it. Roof cleaning starts from £650, depending on the size and type of roof.

Conservatories and solar panels

Moss, algae and dirt don't only affect roof tiles. Conservatory roofs can turn green and let in less light, and solar panels covered in grime and bird mess can look grubby. We clean both, so just ask if you would like them included in your quote.

Mark is a City & Guilds qualified soft wash technician, a member of the Exterior Cleaning Association and carries £5m public liability insurance. For friendly advice or a free quote, call 07584 956981.