Moss vs Algae vs Lichen: What's Growing on Your Roof?

That green or black stuff on your roof isn't all the same. Understanding what's actually growing up there helps you understand why it needs to be removed — and how.

Moss

What it looks like: Thick, green, spongy clumps that can grow several centimetres tall. Often found in shaded areas and between tiles.

Why it's a problem: Moss is the most damaging growth for your roof. It acts like a sponge, holding moisture against your tiles. In winter, this moisture freezes and expands, which can crack tiles. Moss roots can also work their way under tiles, lifting them and creating gaps for water to enter.

Where it grows: Moss loves damp, shaded areas. North-facing roofs and areas under trees are most at risk. It thrives in the UK climate.

Algae

What it looks like: Thin, flat, black or dark green streaks running down your roof. Often mistaken for dirt or staining.

Why it's a problem: While algae doesn't cause as much structural damage as moss, it spreads quickly and makes your roof look dirty and neglected. It can also make tiles slippery and dangerous to walk on.

Where it grows: Algae spreads through airborne spores and can appear on any roof. It's particularly common in humid areas and spreads fastest in warm, wet conditions.

Lichen

What it looks like: Crusty, flat patches that can be grey, green, yellow or orange. Lichen has a rough, textured appearance and bonds tightly to surfaces.

Why it's a problem: Lichen is actually a combination of algae and fungus living together. It bonds extremely tightly to roof tiles and can be difficult to remove without the right techniques. Over time, it can pit and erode tile surfaces.

Where it grows: Lichen prefers clean air and is often found in rural or suburban areas. It grows slowly but is very persistent once established.

Why All Three Need Removing

Regardless of which type is on your roof, they all share some common problems:

• • They all hold moisture against your tiles
• • They all make your home look uncared for
• • They all spread and get worse over time
• • They all reduce your property's kerb appeal and value

How We Remove Them

Different types of growth respond to different cleaning methods. That's why we assess every roof before recommending a treatment:

• • Low pressure cleaning works well for moss and algae on sturdy tiles
• • Manual scraping is often needed for thick moss or delicate tiles
• • Biocide treatment kills all three types at the root and prevents regrowth

The biocide treatment is particularly important for lichen, which can regrow quickly if not killed at the root.