Lichen, Algae or Moss? Identifying What Is Growing on Your Bournemouth Roof

Take a proper look at your roof and you will often spot more than one thing growing up there. Perhaps a spongy green cushion in the tile gaps, dark streaks running down the slope, or crusty grey-green blotches clinging to the ridge. Many people lump all of it together as moss, but these are actually three different organisms, each behaving in its own way.

Knowing which is which helps you understand what your roof is dealing with and why it looks the way it does. It also explains why a proper clean matters. In this guide we will help you tell moss, algae and lichen apart, why Bournemouth roofs are such happy homes for all three, and what can be done about them.

The quick answer: Moss is the thick, green, spongy growth in the gaps between tiles. Algae shows up as flat green film or dark black streaks. Lichen is the tougher, crusty, grey-green growth that clings hard to the surface. All three thrive in Bournemouth's damp coastal air, and all three respond to soft washing.

1. Moss: the thick green cushions

Moss is the one most people picture, and it is usually the easiest to identify. It forms soft, spongy, bright green clumps that gather in the gaps between tiles and along the ridge. Left alone, it can grow into thick cushions that lift at the edges and trap a surprising amount of water.

It loves damp, shaded spots, which is why the north-facing slope of a roof is almost always the worst affected. Around Bournemouth, homes tucked among the pines or shaded by mature trees in areas like Branksome and Talbot Woods tend to gather moss quickly. The constant moisture from the sea air only encourages it.

Moss is more than an eyesore. Because it holds water against the tiles and pushes into the joints, it can gradually work at the roof surface, and when clumps break loose they slide straight into the gutters. Have you noticed your gutters overflowing after rain? Moss debris is often the culprit.

2. Algae: the green film and black streaks

Algae is sneakier than moss because it lies flat against the surface rather than forming clumps. It appears as a thin green film across large areas, or as the dark, almost black streaks that run down so many roofs. Those black streaks are a very common sight on Bournemouth's concrete tiled roofs in particular.

Unlike moss, algae does not need the deep shade of a north slope. It spreads happily across broad areas of the roof, carried on the wind as spores and feeding on moisture and the minerals in the tiles. The mild, humid conditions here on the coast give it plenty to work with all year round.

While algae does not hold water the way moss does, it still darkens and ages the look of a roof considerably. A house can look tired and neglected simply because of algae staining, even when the tiles beneath are perfectly sound.

3. Lichen: the tough, crusty patches

Lichen is the most stubborn of the three. It shows up as crusty, flattish patches, often grey-green or with a slightly leafy, ruffled edge, and it clings extremely tightly to the tile surface. Unlike moss, it does not brush away easily, because it anchors itself hard into the material.

Lichen is a curious thing, being a partnership between a fungus and an algae working together. It grows slowly but is remarkably resilient, and it tends to favour the ridge tiles and the more exposed, sunnier parts of the roof, which is the opposite of moss. You will often see all three organisms sharing the same roof, each in its preferred spot.

Because lichen grips so firmly, it needs proper treatment rather than scraping, which risks damaging the tile. This is one more reason why gentle, chemical-led soft washing is the right approach rather than aggressive physical removal.

4. Why Bournemouth roofs attract all three

The reason local roofs gather such a mix comes down to our particular climate and surroundings. Bournemouth sits on a sheltered stretch of the south coast with mild, damp air, frequent moisture and plenty of tree cover in its greener suburbs. These are close to ideal conditions for organic growth of every kind.

Salt-laden sea breezes keep surfaces humid, the pines and sheltered gardens hold moisture in, and the town's period housing offers plenty of textured clay and concrete tiles for growth to grip. Add in the shade from dormers, chimneys and neighbouring trees, and it is little wonder roofs here need regular attention.

None of this reflects badly on your home. It is simply the nature of living somewhere green, coastal and mild. The trick is to keep on top of the growth rather than letting it establish over many years.

5. Why correct identification matters

Telling the three apart is not just an academic exercise. Each behaves differently, and the mix on your roof affects how the growth should be treated and how quickly it is likely to return. A roof dominated by thick moss needs careful lifting of the growth first, while heavy lichen calls for a treatment that can break its firm grip over time.

Getting this right avoids the temptation to reach for a pressure washer, which is the wrong tool for all three. Blasting moss, algae or lichen at high pressure can crack tiles, strip protective surfaces and force water underneath, causing far more harm than the growth itself. Would you take a jet wash to something you wanted to protect?

A professional eye reads the whole picture, identifies what is present and treats it appropriately, which is why an assessment is always worthwhile.

6. How soft washing deals with the lot

The beauty of soft washing is that it handles all three organisms without harming the roof. It combines low-pressure water with a specialist biocide that kills moss, algae and lichen at the root, rather than simply blasting the surface growth away for it to return.

The biocide keeps working after the visit, continuing to break down spores and growth over the following weeks. This is why soft washing gives such a clean finish and why the results last far longer than a quick physical scrub. For lichen in particular, this slow chemical action is far more effective than trying to prise it off.

Done properly, soft washing leaves a roof looking transformed and keeps it clearer for years, whatever combination of green, black and crusty growth it started with.

• Moss: Thick, spongy green cushions in tile gaps and on shaded north-facing slopes that trap water and clog gutters.
• Algae: Flat green film or dark black streaks spreading across broad areas, common on local concrete tiles.
• Lichen: Crusty grey-green patches that cling tightly to ridges and exposed areas and resist simple brushing.
• Soft washing: Low-pressure water plus biocide that treats all three at the root and keeps working after the visit.

Frequently Asked Questions

Is moss worse than algae for my roof?
Moss tends to cause more physical trouble because it holds water and blocks gutters, while algae is more of a cosmetic problem. Both are worth removing, but heavy moss is usually the more pressing concern.

Why is lichen so hard to remove?
Lichen anchors itself firmly into the tile surface, so it cannot simply be brushed off. A biocide treatment that breaks it down over time is far safer and more effective than scraping, which risks damaging the tile.

Do these organisms damage the tiles themselves?
Over long periods they can contribute to wear, especially moss holding moisture against the surface. Sound tiles are rarely ruined quickly, but leaving growth for years is not wise, which is why regular cleaning pays off.

Will the growth come back after cleaning?
Some regrowth is natural over time, particularly in shaded, coastal spots like ours. A proper biocide treatment slows it considerably, and periodic maintenance keeps the roof clear for the long term.

Can I tell what I have from the ground?
You can often make a good guess, but the shaded areas where moss and lichen thrive are hard to judge from below. A close assessment gives a far clearer picture of exactly what is growing and where.

Not sure what is growing on your roof?
Ben's Roof Cleaning brings over 15 years of experience in safe, effective roof cleaning across Bournemouth and the surrounding area. Get in touch or call 01202 084808 for a free, no-obligation quote.

Knowing your roof, growth and all

Moss, algae and lichen each tell their own story about the damp, mild conditions we enjoy here on the Dorset coast, and each behaves in its own way on your tiles. Once you can tell the spongy green cushions from the flat streaks and the crusty patches, the state of your roof makes a lot more sense. Whatever combination you are dealing with, a careful soft washing treatment clears the lot and keeps your roof looking its best for years to come.