Why Are My Exterior Walls Turning Green?
Walls turn green where they stay damp: shaded, slow-drying elevations, often north or east facing, or near trees. It is common in the UK and is often mainly an appearance issue. It can be cleaned with a controlled softwash rather than high pressure.
Published 24 September 2026
Why is my house turning green?
Green growth appears where a wall stays damp: shaded areas, elevations that dry slowly, north and east-facing walls, and walls near trees and vegetation. Textured and porous surfaces hold moisture and give growth more to cling to.
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Green organic growth is very common on damp external surfaces in the UK and is not a sign that anything has been neglected.
Is the green growth mould or algae?
Homeowners often call several kinds of organic growth mould. On walls, green growth is usually algae, sometimes with moss or lichen, but a visual look is not always definitive. It does not change the approach much: the surface is assessed and cleaned to suit it.
Why does one side of the house go green before another?
Orientation is the biggest factor. Walls that get little direct sun stay damp for longer after rain. The side facing prevailing weather takes more rain, trees shade walls and block airflow, and rainwater run-off from sills, gutters or roof details keeps particular areas wet.
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That is why a house can look spotless at the front and green at the back, or why one gable goes green while the other stays clean.
Can green algae damage walls?
Often it is mainly an appearance and maintenance issue. Persistent damp growth can hold moisture against the surface, so it is worth dealing with, but it does not automatically damage render.
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The cleaning method matters. Aggressive cleaning can do more harm to a wall than the growth itself.
How do you remove green algae from exterior walls?
We assess the surface, then apply a suitable softwash treatment in a controlled way, allow dwell time for it to work, and finish with a low-pressure rinse or natural weathering where appropriate. Surrounding planting and materials are protected throughout.
Why not just pressure wash it?
High pressure can remove visible growth quickly, but it does not suit every render, brick or coating. We choose the process for the surface rather than defaulting to maximum pressure.
How can I reduce green algae returning?
Manage vegetation near the wall where practical, deal with persistent water run-off and keep gutters working so they do not overflow down the wall. Periodic maintenance and a regrowth protection treatment where appropriate help keep walls cleaner for longer.