Roof cleaning guide
Is roof cleaning safe for roof tiles and slate?
Yes, when the correct method is used for the specific tile type. Softwashing is safe for all common UK residential roof materials. Pressure washing is not safe for clay, handmade or natural slate tiles. The damage concerns homeowners have about roof cleaning are almost always about the wrong method being applied, not about professional cleaning itself.
The question of whether roof cleaning is safe for tiles and slate comes up regularly, and the concern behind it is legitimate. Accounts of tiles cracked or dislodged during cleaning, ridge mortar washed out, slate split or colour stripped from concrete tiles do exist, and they represent a genuine risk. However, in virtually every case these outcomes are the result of a single factor: using an inappropriate cleaning method for the roof type in question. Specifically, applying high-pressure washing to tiles that are not suited to it. When professional softwashing is used with the correct biocidal chemistry at low pressure, roof cleaning is not only safe for all common UK residential tile and slate types, it is beneficial. It removes the moisture-retaining, tile-deteriorating biological growth that, left in place, would cause significantly more damage to the tiles over time than any professionally applied softwash treatment.
Softwashing
Low pressure, biocidal solution, garden hose pressure rinse. Safe for all tile and slate types.
- Natural slate
- Traditional clay tiles
- Handmade plain tiles
- Modern concrete interlocking tiles
- Fibre cement and synthetic slate
- Roofs needing ridge mortar repairs
High-pressure washing
Not appropriate for most residential roof types. Risks include:
- Cracking or shattering natural slate
- Fracturing fragile clay tiles
- Washing out ridge mortar
- Dislodging tiles at overlaps
- Stripping surface protection from concrete tiles
- Forcing water under tiles into roof space
Is professional cleaning safe for your specific roof material?
Natural slate
Softwashing is safe for natural slate. Slate is a hard natural stone but it can be fractured by high-pressure water, particularly older slates that have become more brittle. It can also be dislodged from its nail fixings. Softwashing applies no mechanical force to the slate surface, kills biological growth at the root level and rinses at low pressure. DOFF steam cleaning is used for heritage slate where biocidal application requires specialist consideration.
Traditional and handmade clay tiles
Softwashing is safe. Handmade clay tiles are fragile and easily cracked by pressure washing. Many are over a century old on London properties and are irreplaceable with matching units. Softwashing is the only appropriate cleaning method for traditional and handmade clay tiles. The biocidal solution effectively removes moss and algae without any mechanical contact with the tile surface.
Modern concrete interlocking tiles
Softwashing is safe and preferred. Concrete tiles can be pressure washed when in good structural condition and with the pressure and technique controlled carefully, but softwashing produces longer-lasting results by killing spores. Tudor Roof Tiles, as one of the UK's leading tile manufacturers, explicitly advises against pressure washing and recommends low-pressure chemical moss killer application for their concrete and clay tiles. The Nottingham Driveway company's analysis of concrete tile damage confirms that freeze-thaw from sustained moisture is the key concern, which softwashing addresses by removing the moss creating that moisture retention.
Fibre cement and synthetic slate
Softwashing is safe for all fibre cement and synthetic slate products. These materials have surface coatings and protective layers that high-pressure washing strips over time. Always check the tile manufacturer's maintenance guidance before any cleaning. Softwashing is approved by all major fibre cement roofing product manufacturers for biological growth removal.
Industry guidance on safe roof cleaning
The National Federation of Roofing Contractors is the UK's primary industry body for roofing professionals and its guidance is clear: aggressive high-pressure moss removal poses structural questions to roof integrity. The NFRC recommends softwashing and biocidal treatment as the appropriate method for residential roof cleaning precisely because it achieves the cleaning objective without the risks associated with high-pressure methods. When a professional contractor inspects the roof before cleaning, uses the correct biocidal product at the correct dilution and applies it at low pressure appropriate to the roof type, roof cleaning is safe and beneficial for all common UK tile and slate types. Damage during roof cleaning is caused by incorrect method selection, not by professional cleaning itself.
Roof cleaning London
Safe professional roof cleaning across London by Cloud Nine
Cloud Nine inspects every roof before cleaning and selects the correct softwashing method for the specific tile type. We never use high-pressure washing on clay or natural slate. Contact us for a free assessment and quote.
Part of our guide
Roof cleaning help and guidance
Everything London homeowners need to know about roof cleaning.
Back to the guide