Roof soft washing

Moss, lichen and algae killed and cleared from concrete and clay tiles and slate at low pressure, without forcing water under tiles. UK guide prices.

In short: Roof soft washing is the low-pressure treatment of roof tiles or slates with a biocide that kills moss, lichen and algae, with loose moss cleared and the roof rinsed gently. It is for homeowners whose roofs are green, black or matted with moss. In the UK, roof soft washing usually costs £400 to £800 for a semi-detached house and £600 to £1,000 or more for a detached house.

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Moss on a roof is more than cosmetic. Thick moss holds water against the tiles, can lift tile edges and block gutters and downpipes when it washes off, and in cold weather the trapped water can freeze. Lichen and algae are thinner but still hold moisture and make the roof look tired. Concrete tiles, which are porous and slightly rough, are the most prone to growth.

Pressure washing a roof can strip the surface from concrete tiles, crack old clay tiles and slates, and drive water up under the laps into the roof space. Soft washing kills the growth at low pressure instead. Heavy moss is usually brushed or scraped off first, then the biocide is applied, and the remaining growth dies back and is washed away by rain over the following weeks.

What is included

Inspection of the roof covering and any slipped, cracked or missing tiles
Hand removal of heavy moss clumps from tiles, ridges and valleys
Low-pressure biocide treatment of the whole roof covering
Protection of plants, conservatories and surfaces below
Clearing moss and debris from gutters after the treatment
Rinsing of windows, sills and paintwork affected by run-off
Report of any roof defects noticed during the work

Who it is for

Concrete tile roofs with moss, lichen and green algae
Clay tile and slate roofs where high pressure could cause breakage
Roofs under or near trees that green up quickly
Owners selling a property who want the roof to look cared for
Roofs where moss is repeatedly blocking gutters

How much does it cost?

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. Steep pitches, three-storey buildings and roofs needing scaffold or a cherry picker cost more. See our full cost guide.

How it works

How roof soft washing works, step by step

Assess the roof

The covering, pitch, height and safe means of access are assessed, and any defects noted before work starts.

Clear heavy moss

Thick moss is removed by hand or with a scraper, working with the laps so tiles are not lifted.

Treat at low pressure

The biocide is applied evenly across the roof from a safe working position, avoiding water being forced under tiles.

Clear and rinse

Gutters are cleared of moss and debris, and windows and plants below are rinsed down.

Roof soft washing: FAQs

Is roof soft washing safe for old clay tiles and slate?

It is generally the safest cleaning method for them, because it does not rely on water pressure. Old clay tiles and slates can be brittle, so the amount of walking on the roof is kept to a minimum and access is from ladders, roof ladders or a cherry picker where possible. Any already cracked or slipped tiles are noted before work starts.

Does the roof look clean straight away?

Moss that has been brushed off is gone straight away, but lichen and algae often look darker or patchy at first. As the biocide works, the growth dies back and is washed away by rain over several weeks or a few months. Slow-acting biocides are often chosen for roofs because they keep working for longer.

Should I have my roof coated after cleaning?

Roof coatings are sold as a way to keep tiles cleaner, but they are not always necessary and can change how the roof looks and breathes. A clean, sound roof can simply be given a maintenance biocide treatment every few years. If you are considering a coating, check that it is suitable for your tiles and does not affect any warranty.

Will soft washing kill the moss in my gutters?

The treatment will kill moss that the solution reaches, but dead moss and debris still need to be physically cleared from gutters and downpipes, otherwise they block and overflow. Gutter clearing after a roof clean is part of doing the job properly, as loose moss washes down for weeks afterwards.