This article is part of our typical property defects series and based upon issues our surveyors regularly locate during RICS Level 2 Surveys, Level 3 Surveys and Defect Analysis Reports.
Moss and lichen are commonly found on roofs, particularly on older properties, shaded elevations, and roofs close to trees.
At first glance, moss and lichen may seem like a minor cosmetic issue. In some cases, they are. However, if left to build up over time, they can contribute to roof deterioration, blocked gutters, water retention, and future maintenance problems.
The key is understanding when moss and lichen are simply surface growth, and when they may be affecting the performance of the roof covering.
What is moss and lichen?
Moss is a soft green plant that often grows in damp, shaded areas. On roofs, it tends to collect between tiles, along laps, in valleys, and around gutters.
Lichen is a slower-growing organism that often appears as pale, white, grey, yellow, or green staining on roof tiles. It tends to attach firmly to the surface of the tile.
Both are common on roof coverings and external surfaces, especially where there is limited sunlight, nearby vegetation, or poor airflow.
Why does moss and lichen grow on roofs?
Moss and lichen usually grow where moisture is retained.
Common causes include:
- shaded roof slopes;
- nearby trees;
- damp or sheltered elevations;
- north-facing roof slopes;
- older or weathered roof tiles;
- poor roof maintenance;
- blocked gutters or valleys;
- areas where debris collects.
Roofs beneath or close to mature trees are particularly prone to moss growth because falling leaves, shade, and moisture create ideal conditions.
Is moss and lichen a problem?
Not always.
A light covering of lichen or minor moss growth may not require urgent action. However, heavier moss growth can become a maintenance issue.
Moss can hold moisture against the roof covering. Over time, this can increase weathering to tiles, encourage frost damage, and place additional stress on older or fragile roof coverings.
Loose moss can also fall into gutters, downpipes, valleys, and drainage channels. This can cause blockages, leading to overflowing rainwater goods and possible damp issues to the external walls below.
What signs should you look out for?
Homeowners and buyers should look for:
- heavy moss growth across roof slopes;
- moss collecting in gutters or valleys;
- blocked or overflowing rainwater goods;
- slipped, cracked, or damaged tiles;
- staining to walls below gutters;
- damp patches internally near roof areas;
- plant growth around roof junctions;
- debris collecting behind chimneys or parapets.
Moss and lichen should be considered alongside the overall roof condition. If the roof tiles are already cracked, delaminating, slipping, or heavily weathered, moss growth may be contributing to further deterioration.
Can moss damage roof tiles?
Moss itself does not usually damage tiles immediately. The concern is the moisture it retains.
When moss holds water against the tile surface, the roof covering may remain damp for longer periods. During colder weather, this moisture can freeze and expand. This can accelerate wear, especially on older concrete tiles, clay tiles, or tiles that are already deteriorating.
Lichen can also attach to tile surfaces and may contribute to surface weathering if aggressive cleaning methods are used to remove it.
Should moss be removed?
Yes, especially where the moss growth is heavy, blocking gutters, affecting drainage, or sitting around vulnerable roof details.
However, removal should be carried out carefully. Roof tiles can be fragile, and aggressive pressure washing can damage the tile surface, force water beneath the roof covering, or reduce the lifespan of older tiles.
A competent roofing contractor should assess the roof and use an appropriate method of removal. This may involve careful manual removal, clearing gutters and valleys, and applying a suitable treatment where appropriate.
Should you pressure wash a roof?
Pressure washing should be approached with caution.
Although it may improve the appearance of the roof in the short term, it can damage tiles, strip away protective surfaces, disturb laps, and force water into areas that are not designed to receive direct water pressure.
For older or weathered roofs, pressure washing may cause more harm than good. A safer and more considered cleaning method is usually preferable.
What about gutters and downpipes?
Moss and lichen often become a problem when they enter the rainwater system.
Blocked gutters can overflow during rainfall. This can cause water to run down external walls, increasing the risk of damp, staining, algae growth, and deterioration to brickwork, render, and pointing.
Gutters, valleys, outlets, and downpipes should therefore be checked and cleared as part of routine roof maintenance.
Should buyers be concerned?
Moss and lichen should not automatically put you off buying a property.
In many cases, it is a common maintenance issue. However, buyers should consider whether the growth is light and manageable or whether it is part of a wider roof condition problem.
If the roof covering is old, heavily weathered, damaged, or nearing the end of its useful life, moss and lichen may indicate that roof maintenance or repairs are needed.
A survey can help identify whether the issue is minor, whether roof cleaning is advisable, or whether more significant roofing works should be considered.
How can moss and lichen be prevented?
It may not be possible to prevent moss and lichen completely, especially where a property is close to trees or in a shaded location.
However, the risk can be reduced by:
- keeping gutters and valleys clear;
- removing fallen leaves and debris;
- cutting back overhanging branches where appropriate;
- improving airflow and sunlight where possible;
- arranging periodic roof inspections;
- dealing with slipped or damaged tiles early;
- avoiding long-term build-up of moss.
Regular maintenance is usually the best approach.
Stokemont’s advice
Moss and lichen are common roof issues, but they should not be ignored where growth is heavy or where it is affecting drainage.
The main concern is not simply how the roof looks, but whether the growth is holding moisture, blocking gutters, or contributing to wider roof deterioration.
At Stokemont, we explain property defects clearly and practically, so you understand what is happening, what it may mean, and what action may be needed.
Concerned about moss or lichen on your roof?
If you are buying a property, selling a property, or concerned about the condition of your roof, Stokemont can help.
Contact Stokemont today to arrange a property survey or defect inspection and receive clear, professional advice before minor issues become more costly to resolve.
