Roof cleaning Bristol & Bath. Soft-wash, not high-pressure
Tiled, slate, metal and GRP roofs across the BS and BA postcodes. Chemistry-led soft-wash. We do not jet-wash roofs. Pressure breaks tile crowns, strips factory granules and voids the manufacturer warranty. Our biocide-led process kills the organism at root level and leaves the surface that is keeping your house dry intact. Free survey on 07763 741067.
Should you pressure wash a roof?
No, almost never. Pressure breaks tile crowns, strips factory granules off the slurry coat, drives water under the laps, and voids the warranty on Marley, Redland, Sandtoft and Russell tiles. The clean looks great for nine months and the moss is back faster than it was before. Soft-wash chemistry kills the algae and lichen at root level. The visible result builds up over six to twelve weeks of British weather and lasts four to six years.
What you can see from the pavement
You have probably noticed three things. Black streaks running vertically down the slope. That is Gloeocapsa magma, a cyanobacterium that feeds on the calcium-carbonate fillers in concrete tile and on airborne organic dust. Green and grey cushions of moss colonising the lower courses and the north-facing pitches, where the roof never fully dries. Gutters that overflow in heavy rain because last winter's moss has dropped into the hoppers and dammed the downpipes.
Left alone, moss holds moisture against the tile, speeds up freeze-thaw spalling, and shortens a 60-year roof to 35. We fix the cause, not the symptom. Chemistry-led, not pressure-led. Owner-operator, Bristol-based, working across the BS and BA postcodes.
We used to run cold-water lances on lichen-heavy roofs in our first year. Switched after a 1965 Marley Modern roof in BS6 came back patchy six months later because the surface granules had thinned in the cleaned bands. The moss came back into those weakened patches first. Now we are chemistry-only on tiles. Slower visible result, dramatically better long-term outcome.
Why high-pressure roof cleaning is the wrong answer
We get asked at least once a week to put right a roof that a "jet-wash man" has destroyed. The damage pattern is consistent and well documented across the Bristol housing stock.
Broken tile crowns and nibs
A 2,500 to 3,500 PSI lance applied to a 30-year-old Marley Modern concrete tile fractures the crown and chips the leading edge. The damage is invisible from the ground but it sits there as a leak path the next time we get a driving rain off the Severn.
Eroded surface granules
Concrete and clay tiles are protected by a factory-applied surface coat. Coloured slurry on concrete, vitrified slip on clay. High-pressure water strips that coat in a single pass. Once the substrate is exposed the tile becomes more porous, holds water longer, and regrows moss faster than before the clean. We have seen visible regrowth within nine months on pressure-cleaned roofs against four to six years on properly soft-washed ones.
Spore-driven recolonisation
A pressure jet does not kill spores. It atomises and embeds them. The "clean" roof you see on day one is reseeded by day thirty.
Voided warranties
Marley, Redland, Sandtoft and Russell all explicitly warn that abrasive cleaning voids the manufacturer guarantee. BS 5534:2014+A2:2018 (the Code of Practice for slating and tiling) and NHBC and LABC maintenance guidance both reference non-abrasive cleaning and biocidal treatment as the appropriate route. Pressure cleaning a tiled roof is not endorsed by any UK tile manufacturer.
Water ingress
A roof is a drainage system, not a waterproof membrane. The lap, side-lap and head-lap details are designed for rainwater running down the surface. They are not designed for a 25-degree fan of water driven up under the tile. We have surveyed three properties in BS6 in the last year with ceiling damage that traced directly back to a high-pressure roof clean.
If you want a roof clean that will still be clean in five years, it must be biocide-led.
Surfaces we cover
Concrete interlocking tiles
Marley Modern, Redland 49, Sandtoft Standard Pattern, Russell Cambrian. The most common roof type in post-1965 Bristol estates (BS5, BS7, BS9, BS10, BS13, BS14, BS16, BS31, BS34). Standard sodium hypochlorite at the right dilution, extended dwell, gentle rinse. Manual scrape on heavy lower-course moss after the kill.
Clay pantiles & plain tiles
Sandtoft, Hinton Perry & Davenhill, Dreadnought. Found across the older Bath terraces and BA2 cottages. Reduced dilution because the vitrified slip is more easily damaged than concrete, and gentler rinse. Clay holds the kill chemistry well so dwell is a touch shorter.
Welsh and Spanish slate
Natural slate is dense and durable, but lichen attaches mechanically. We treat with a slate-safe biocide and accept the lichen ghosts off over six to twelve months as the British weather unbinds it from the slate face. Scraping live lichen off slate damages the slate, so we do not do it.
Bath stone slates
Limestone slates on Listed Bath properties are highly susceptible to delamination if treated incorrectly. We use a low-concentration, neutral-pH biocide and the no-touch protocol. Biocide application only, no rinsing, no scraping. We will refuse the job rather than risk a Grade II roof.
Profile metal sheet
Agricultural and industrial roofs (box-profile, Kingspan, Eternit fibre-cement). Soft-wash with surfactant-modified biocide and a low-pressure rinse. Common across South Gloucestershire farms and small Avonmouth industrial units. We work from MEWP for fibre-cement because the substrate is fragile.
GRP and fibreglass
Flat dormers, garage roofs, conservatory cappings. Soft-wash only. Pressure cracks the gel coat. Common detail to clean alongside a main roof clean because the dormer cheek catches the algae first on north pitches in Henleaze and Cotham.
If we cannot clean your roof safely, we will tell you on the survey. We do not take jobs we cannot guarantee.
How we pick the method
The chemistry, dilution and dwell are matched to the substrate, the organism load, and the weather on the day. There is no single recipe.
Standard NaOCl soft-wash (concrete tile, brick)
Sodium hypochlorite at the right available-chlorine percentage, blended with a non-ionic surfactant for dwell. Applied through a 12V soft-wash pump at fan-spray pressure (under 60 PSI at the nozzle). Dwell 15 to 45 minutes depending on lichen load. Rinse at low volume, never high pressure.
Reduced-dilution soft-wash (clay tile, slate)
Same chemistry, lower concentration. Slate and clay both want a gentler kill. Reduced rinse pressure. We accept slower visible results in exchange for keeping the surface granules and vitrified slip intact.
Heritage no-touch protocol (Bath stone slate, listed properties)
Lowest viable hypochlorite concentration. Application only, no rinse, no manual moss scrape. The chemistry weathers off naturally over weeks. Used on Bath stone slates and any listed roof where conservation officers require the gentlest method on file.
Manual moss scrape (heavy moss colonies)
Plastic blades only. Never wire. After the biocide has killed the colony at root level we scrape the dead moss from the lower three or four courses on the north pitch and bag it as controlled waste under our EA Upper-Tier Waste Carrier registration. Leaving dead moss in place blocks gutters within one autumn.
What drives the cost
We will not publish made-up "from £X" figures because every roof is genuinely different. Here is the honest cost-driver list.
- Roof footprint. A typical Bristol semi in BS5 or BS6 has a roof footprint of around 80 m². A detached family home in BS9 or BA1 is typically 130 to 160 m².
- Height and pitch. A two-storey roof reachable with a telescopic lance from the lawn is the cheapest job we do. A three-storey townhouse in Cliftonwood that needs a MEWP with a road licence is materially more expensive.
- Roof complexity. Hipped roofs, valleys, dormer cheeks, multiple chimney stacks all add time. A simple gable with two pitches is faster than the same area broken up by four dormers.
- Severity of growth. Heavy lichen on a north-facing slate roof needs a stronger product and a longer dwell. Light algal staining on a south-facing concrete tile is a single-pass job.
- Scaffold requirement. Where MEWP access is impossible (narrow lanes, overhead cables, listed terraces in central Bath) and the roof cannot be reached from ground, scaffold is the safe option. Hire is passed through at cost with no markup.
- Listed Building Consent. Grade II properties may require Listed Building Consent for any roof work. We do not start without it.
Every quote is fixed before we begin. No day-rate creep, no "we found more than expected", no surprises on the day. Indicative range for a standard three-bed semi roof clean is £450 to £850 depending on access and growth load. Bigger detached homes in BS9 or BA1 typically run £800 to £1,400. See the pricing logic and guarantee for the full detail.
Honest hedge. Most of the time those ranges hold. Heritage roofs, scaffold-required townhouses and four-storey Bath frontages sit higher because the access is the access.
Where we work
The Bristol and Bath corridor sits in one of the dampest, mildest microclimates in lowland England. Mean annual rainfall is around 850 mm at Filton and over 950 mm on the Mendip flanks above Bath. Prevailing south-westerlies carry spore-laden air off the Severn estuary and dump it on every windward slope from Avonmouth eastwards. The steep north-south streets of Clifton, Cotham, Redland and Bishopston funnel that moist air uphill. It condenses overnight on cool tile surfaces and feeds the algae through the morning.
10 cities and towns we cover
Bristol, Bath, Keynsham, Saltford, Portishead, Clevedon, Thornbury, Nailsea, Yate and Chew Valley. See areas we cover for the full list.
Sub-areas and neighbourhoods we cover regularly
Clifton, Redland, Cotham, Bishopston, Henleaze, Westbury-on-Trym, Stoke Bishop and Sneyd Park in Bristol; Lansdown, Bathwick, Widcombe and Combe Down in Bath.
Bath has its own challenge. The Bath stone slate roofs of Lansdown, Bathwick, Widcombe and Combe Down are limestone. Soft, calcareous, and highly vulnerable to delamination if you put the wrong chemistry on them or, worse, a pressure washer. Listed Building Consent rules apply to any external alteration of a listed property, and Bath & North East Somerset Council interprets "alteration" broadly. We will check the listing and, where required, will not start until consent is in place.
Recent roof work
BS9, Stoke Bishop. 145 m² concrete tile, January 2026.
Marley Modern concrete tile, 1972 build, never previously cleaned. Heavy lichen rosettes across both pitches, dense moss in the lower three courses on the north pitch. MEWP access from the driveway. Standard NaOCl soft-wash, 35-minute dwell, manual scrape on the lower north courses, residual post-treat. Six-week and twelve-week follow-up photos showed full lichen weather-off. Customer signed off in writing.
BA2, Widcombe. 90 m² Bath stone slate, March 2026.
Grade II listed Georgian terrace. Bath stone slate roof with light to moderate biological soiling. Listed Building Consent obtained before mobilisation. Heritage no-touch protocol. Lowest viable dilution, application only, no rinse, no scrape. Conservation officer signed off the method statement before work started. Result builds up over twelve weeks as the chemistry weathers through.
BS6, Cotham. 95 m² Welsh slate, February 2026.
Victorian terrace, original Welsh slate, heavy lichen on the front pitch. Slate-safe reduced-dilution biocide, accepted four to six month visible weathering window. Pole-camera survey before and after.
Frequently asked questions
Will the moss come back?
Yes, eventually. The spores are airborne and your roof is outside. The point of a soft-wash treatment is not eternal sterility. It is to reset the surface and leave a residual biocide that suppresses regrowth. Properly treated, a Bristol roof is visibly clean for four to six years before another light maintenance treatment is sensible. A pressure-cleaned roof typically regrows within 9 to 18 months because the surface is more porous than before.
What chemicals do you use, and are they safe for pets and plants?
The active ingredient is sodium hypochlorite at a controlled dilution, with a non-ionic surfactant to help wetting. Sodium hypochlorite is the same active used in domestic bleach and many drinking-water treatment plants. It breaks down to salt and water within hours of application. We pre-wet vulnerable plants, sheet over koi ponds and water features, and ask you to keep pets indoors during application and for two hours after.
How long until I see results?
Heavy algal staining looks noticeably different the same day. Lichen and dead moss take longer. Typically six to twelve weeks of normal British rainfall for the dead growth to weather off properly. This is the trade-off of doing it without high pressure: slower visible change, dramatically better long-term result. We send a six-week and twelve-week follow-up so you can see the curve.
Will it damage solar panels?
No. Soft-wash chemistry at our dilutions is panel-safe. We routinely mask panels during application and rinse them gently afterwards. We can clean the panels themselves at the same visit if you want. Most of the time they have lost five to fifteen per cent annual output to bird droppings and algal film.
Do I need scaffolding?
Usually not. Most Bristol and Bath roofs are reachable by MEWP from a driveway or quiet road. Scaffold becomes necessary on narrow listed terraces in central Bath and Clifton, on properties where overhead cables block boom access, and on jobs where the customer wants concurrent gutter or fascia work. We tell you at survey which access route is needed and itemise the cost.
Related services
Most roof cleans pair well with a gutter clear and a render soft-wash on the same visit because the access kit is already on site.
- Driveway & patio cleaning
- House render & wall cleaning
- Soft washing
- Gutter, fascia & soffit cleaning
- Conservatory cleaning
- Window cleaning
- Solar panel cleaning
- Hot washing
- K-Rend & silicone render cleaning
- Commercial exterior cleaning
Book your free roof survey
Free site survey, drone or pole-camera footage emailed to you regardless of whether you book the clean. We respond within one working day. Most surveys booked inside the same week. Phone 07763 741067, send a postcode via the quote form for a survey, WhatsApp +44 7763 741067, or email enquiries@bristolandbathexteriorsolutions.co.uk.