Comparisons · 4 min read · Updated 6 November 2026
Soft washing roofs: concrete tiles, clay, slate and fibre cement
Why roof type matters
Different roofing materials react differently to water, pressure and chemicals. Some are porous and soak up solution, some are hard and smooth, and some are fragile or may contain asbestos. A contractor should identify the roof type before quoting, because it affects the method, the product, how long the job takes and whether it is safe to work on at all.
If you are not sure what your roof is made of, a few clear photos from the ground and the age of the house are usually enough for a contractor to tell.
The main roof types compared
| Roof type | Common on | Soft wash suitability | Key cautions |
|---|---|---|---|
| Concrete interlocking tiles | Most post-war homes | Good | Surface can erode under high pressure |
| Plain clay tiles | Older and period homes | Good with care | Older tiles can be soft and spall |
| Natural slate | Victorian and Welsh slate roofs | Good with care | Slates can slip, nail fatigue on old roofs |
| Fibre cement slates | Many 1970s to 1990s homes | Depends on age | Pre-2000 may contain asbestos |
| Asbestos cement sheets | Garages, outbuildings, farm buildings | Specialist only | Fragile, no high pressure |
| Felt and flat roofs | Extensions, garages | Usually fine at low pressure | Check seams and condition |
Concrete tiles
Concrete interlocking tiles, often with a granular coloured surface, cover a large share of UK homes. They hold moss in the gaps and lichen on the surface. High-pressure washing can strip the surface coating and roughen the tile, which helps moss come back faster. Soft washing kills the growth and lets most of it weather away, often after loose moss has been removed by hand.
Older concrete tiles sometimes look patchy after cleaning because the coloured surface has worn unevenly over decades. That is ageing rather than damage, and it is worth knowing before the job so expectations are realistic.
Clay tiles and natural slate
Handmade and older machine-made clay tiles can be soft and porous, and some may already be spalling from frost. Natural slate is hard and sheds water well, but old slates can be fragile and the nails holding them corrode over time. Both benefit from low-pressure treatment that avoids walking on the roof where possible. A careful contractor will note slipped or broken tiles and slates before and after the clean.
Fibre cement and asbestos cement
Fibre cement slates and sheets made before 2000 may contain asbestos. In good condition and undisturbed they are generally low risk, but weathered surfaces can release fibres if scraped, brushed hard or pressure washed. HSE guidance for cleaning weathered asbestos cement roofing describes low-pressure biocide application followed by gentle methods, keeping the surface wet, and says high-pressure jetting is only appropriate in exceptional circumstances by specialist contractors.
- Get the roof tested if age and material suggest asbestos
- Never walk directly on asbestos cement sheets, which are fragile
- Avoid high-pressure washing and dry brushing
- Control and collect slurry and debris
- Use a contractor experienced with asbestos cement
Access and safety on any roof
Whatever the material, roofs are dangerous places to work. Wet moss and freshly treated tiles are slippery, and many roofs have fragile areas such as rooflights, old sheets and valley gutters. Under the Work at Height Regulations 2005, work at height must be planned so that the risk of falls is controlled, and the safest option, such as working from the ground or from a platform, should be used where reasonably practicable.
- Many roofs can be treated from the ground or a cherry picker
- Scaffold may be needed for steep or tall roofs
- Roof ladders and fall protection are used where working on the roof is unavoidable
- Fragile roofs must never be walked on directly
- Moss and debris should be cleared from gutters afterwards
Should you coat a roof after cleaning?
Roof coatings and sealers are often sold alongside cleaning. Some can help a concrete tile roof look uniform, but they are not always needed and some can trap moisture or affect how tiles behave. Check the roof manufacturer's guidance and get advice before agreeing to a coating. On clay, slate and historic roofs, coatings are generally not recommended.
As a guide, roof soft washing usually costs £400 to £800 for a semi-detached house and £600 to £1,000 or more for a detached house, with steep pitches, three-storey buildings and specialist roofs costing more.
Frequently asked questions
How do I know if my roof contains asbestos?
You cannot tell for certain by looking. Fibre cement slates and corrugated sheets installed before 2000 may contain asbestos, particularly on garages and outbuildings. A sample can be tested by an accredited laboratory, usually for a modest fee. If the roof is in good condition and not disturbed, it is generally low risk, but cleaning should only go ahead using appropriate low-disturbance methods.
Can a slate roof be soft washed?
Yes, usually. Natural slate is hard and generally tolerates low-pressure biocide treatment well. The main concerns are the age of the roof and its fixings, as old slates can slip if disturbed and walking on them can cause breakages. Contractors often work from access equipment rather than on the roof itself, and they should record any loose slates.
Does soft washing damage concrete roof tiles?
Not when done properly. Low-pressure treatment with a suitable biocide does not erode the tile surface the way high-pressure washing can. Moss and lichen die and weather away over the following weeks. Some old, heavily weathered concrete tiles may look patchy after cleaning because their surface coating has already worn, which is a sign of age rather than damage from the clean.
roof types concrete tiles slate asbestos cement
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