Moss on a roof rarely matters, according to the NFRC, and only needs removing if it blocks gutters or drainage. The NFRC warns against pressure-washing because it can crack tiles and strip their protective surface. If it must go, have a roofer remove it by hand and check the drainage while they are up there.
Moss on a roof looks like a problem, but according to the National Federation of Roofing Contractors (NFRC), it rarely actually is one. It becomes a genuine issue only when it builds up enough to block gutters, valleys or other drainage points, which is what actually causes damage, not the moss itself sitting on the tiles.
When moss is genuinely a problem
- It is blocking gutters or drainage points. This is the main real risk: trapped moss and debris stop water draining properly, which can force it back up under tiles instead of running off the roof.
- It is building up thickly in roof valleys, where water naturally concentrates, since a valley already carries more water than a flat run of tiles and moss narrows the channel further.
- It is holding moisture against the tiles for extended periods, which over a long time can affect tiles that were already ageing or damaged in other ways.
When it is genuinely just cosmetic
A light covering of moss across a roof, particularly on the shaded, north-facing side, is extremely common in the UK’s damp climate and is not, on its own, a sign anything is wrong. Plenty of roofs carry moss for years without it causing any actual damage, and removing it purely for appearance is a choice, not a necessity.
Why the NFRC warns against pressure washing
The instinctive fix, blast it off with a pressure washer, is exactly what the NFRC advises against. Jet-washing a roof can crack or dislodge tiles under the force of the water, and on many modern concrete and clay tiles it strips away the protective lamination finish that helps the tile shed water and resist weathering, which shortens the tile’s working life rather than extending it. Walking across the roof to reach mossy patches adds further risk of cracking tiles underfoot, particularly older or more brittle ones.
The safer approach
If moss genuinely needs addressing, because it is blocking drainage or building up in a valley, a professional roofer will typically:
- Remove it by hand or with a soft brush, working carefully rather than blasting it off.
- Clear gutters and valleys properly while they are up there, since this is usually the actual point of the job.
- Check the tiles and roofline for any damage moss build-up may have caused or masked, such as a slipped tile or a blocked outlet.
This is a slower process than jet-washing, but it does not risk cracking tiles or stripping their protective finish, and it deals with the drainage problem that actually matters rather than just chasing appearances.
Getting a proper assessment
If you are not sure whether the moss on your roof needs action, get a roofer up there for a proper look rather than guessing from the ground or reaching for a pressure washer yourself. Look for membership of the NFRC, whose members follow exactly this kind of guidance rather than the quick, damaging fix. We check trade body membership and independent reviews when we research our Top 5 pages, so a page for somewhere like Poole or Torquay is a fast way to find a roofer who will assess it properly rather than just sell you a clean.
Frequently asked questions
Is moss on a roof bad?
According to the National Federation of Roofing Contractors (NFRC), moss on roof tiles rarely presents a real problem and is mostly a cosmetic issue. It only becomes a genuine concern when it builds up enough to block gutters, valleys or other drainage points, which can lead to water backing up under tiles.
Should I pressure wash moss off my roof?
No. The NFRC specifically warns against pressure-washing or jet-cleaning a roof, since the force involved can crack or dislodge tiles, and it can strip the protective lamination finish on many modern roof tiles, which shortens their lifespan rather than protecting it.
How do professionals remove moss from a roof safely?
A reputable roofer will typically remove moss by hand, using a soft brush rather than a pressure washer, and inspect the tiles and drainage points at the same time to check for any damage or blockages moss has caused. This is a slower, more careful process than jet-washing but avoids the damage that method can cause.
Can I remove roof moss myself?
It is not recommended. Getting onto a roof safely needs proper access equipment, and walking on tiles to reach mossy areas is exactly the kind of unnecessary foot traffic the NFRC warns can crack tiles. It is a job better left to a professional with the right access equipment and roofing knowledge.
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About the author
Stu Clark
Stu spent over 15 years in the trades, working as a plumber before running his own plumbing and bathroom renovation company with a team of eight. He founded Top5Trades to give homeowners the kind of shortlist and straight advice you would get from someone who has actually done the work. More about us →