The short answer
The gentlest way to clean a slate roof is to lift moss off by hand with a soft brush, apply a biocide at low pressure and let it work over several weeks. Slates should never be walked on more than necessary, jetted at close range or scraped with metal tools. Loose, cracked or slipped slates are noted and repaired before the clean is finished.
Why slate is tough and fragile at the same time
Natural slate is a dense, fine-grained rock that barely absorbs water, so it does not suffer from frost in the way a porous tile can. MyBuilder's slate roof guide, updated on 21 August 2026, gives a well-fitted slate covering 80 to 100 years or more, and Welsh slate gets credit for outlasting a century. The stone itself is rarely what fails.
What fails is everything holding it up. Slates hang from battens on nails, and on an old roof those nails may have rusted to a fraction of their original thickness. The slate can look perfect and still be held by one thin spike. Add the fact that slate is brittle underfoot, snapping where it spans a gap between battens, and the roof becomes a surface to treat with care.
Everything about the cleaning plan follows from that. Slate does not need much cleaning to look well, and what it does need must be done without weight, force or sharp tools.
Hand work first, chemistry second
On a slate roof, thick moss is lifted by hand. The roofer works from a ladder or roof ladder, sliding a soft brush or a wooden tool under the moss and easing it out rather than raking it. Moss often grows in the overlaps between slates, and a sharp edge dragged along the lap can chip the bottom corner of the slate above. A slate that is chipped or lifted gets water behind it.
Once the bulk has gone, a biocide goes on at low pressure and is left to kill whatever remains, including the algae and lichen that give slate its patchy grey-green stain. Within a few weeks the roof lightens and the remaining growth falls away with rain. Rushing this stage with a jet is how slates end up cracked, how nails get loosened and how spray gets driven beneath the overlaps and onto the battens. A slow job is a cheap insurance against all three.
Many of these steps are shared with other roofs, and you can read the comparison on our page about moss removal methods, but slate pushes every point harder than concrete does.
What it costs
MyBuilder's roof cleaning guide, updated on 21 August 2026, gives a typical UK range of £500 to £1,000 for cleaning a slate roof, higher than the £400 to £750 it shows for tile. The difference reflects slower, more careful work and the extra time on ladders. The same guide lists soft washing at £15 to £20 per m² and warns that pressure washing at £10 to £15 per m² may damage delicate tiles.
| Roof type | Typical UK range |
|---|---|
| Slate roof | £500 to £1,000 |
| Tiled roof | £400 to £750 |
| Pitched roof, general | £450 to £850 |
These bands are national, so use them as a sense-check. Pitch, height, access and the quantity of growth all change the figure on a real house.
Old roofs, nails and what a survey will find
A survey before cleaning matters more on slate than on any other covering. From the ground you can often see slipped slates, which sit lower than their neighbours and show a bright strip of the batten. Up close, we look for slates that rattle, nail heads that have shown through, hairline cracks and cracked mortar on ridge and hip. A slate cleaned and left in that state may slide out the first windy week.
It is also the moment to talk about what the cleaning will not fix. Removing moss from a roof with failed fixings is rather like painting a fence with rotten posts. If the slates need re-fixing, or the covering has little life left, the better outcome is usually a repair first and a clean second. Our advice is always the least work that cures the fault, and sometimes that means re-fixing a dozen slates, not touching the moss at all.
Cleaning will also reveal damage that the moss was hiding, which is another reason to agree that possibility in advance.
Solar panels, listed roofs and other complications
Slate roofs often carry other things. Solar panel brackets are screwed through the covering into the rafters, and the gap behind the array is a favourite place for moss and nesting birds. Our page on solar panel bird proofing covers that edge of the roof and how cleaning around the panels works.
A listed house, or one within a conservation area, makes the method and the materials matter more still. Cleaning itself is normally maintenance, but anything that changes the slate, such as replacing it or altering the fixings, can need consent from the council. See cleaning listed roofs for the usual questions, and check with Swindon Borough Council's planning team before work if you are unsure.
Insurance, regrowth and next steps
Two questions follow most slate cleans. The first is whether insurance will pay if moss has already damaged the roof, and the answer is covered on moss damage and insurance. The second is how soon moss comes back, which depends on shade and damp more than on how well the roof was cleaned; see will moss grow back for the realistic picture.
To have a slate roof looked at, ring 01793 626096 or message us photos through WhatsApp. The visit ends with a written quote and survey pictures of your own slates, and anything we then do is under a ten-year guarantee on workmanship. Cleaning is only one part of the work we do; the full list sits under roof cleaning and moss removal, and if a roof does not need cleaning, you will be told. Slate that has weathered well can simply be left to age, with an annual look from the ground, a pair of binoculars and a clear gutter.
One last practical point. Whoever cleans your roof, ask how they will get onto it and what they will use to hold their weight. On slate, the honest answer is a roof ladder or a tower, never a boot on the slates themselves.