Most homeowners ask this before anything else. You want a clean roof, but you do not want to pay for damaged tiles. The honest answer is that softwash is a sound method when a skilled team does it properly. However, the result depends on how the work goes, so it pays to know what to look for.
What softwash actually means
Softwash cleans with chemistry rather than force. Because of that, a team sprays a biocide at low pressure, so it reaches the moss, algae and lichen on the tile surface. The treatment kills the growth, and rain then washes the dead material away over the following weeks.
Our own roof cleaning service uses a sodium-hypochlorite-based solution at a controlled dilution. The water pressure is similar to a garden hose, which is the key difference from a jet wash. A jet wash cleans by blasting the surface, while softwash lets the treatment do the work.
Why pressure is the real danger to tiles
Manufacturers agree on this point, and the reasons are practical, since force harms the surface. Wienerberger, which makes clay roof tiles, tells homeowners to avoid high-pressure jet washers. It says the spray can damage the tile finish and strip the colour from concrete tiles.
Marley, a large UK maker of concrete and clay tiles, goes further, while it also warns about water entry. It says most roofing professionals do not recommend pressure washing, particularly for older or more delicate tiles. The jets can also force water and debris into the roof structure, and spray aimed upwards can lift tiles at the laps.
The NFRC, the trade body for roofing contractors, makes a similar point, although it focuses on foot traffic. It warns that power washing can damage a roof, especially when foot traffic cracks the tiles as well. We compare the two methods in our guide to softwash vs pressure washing.
Where the manufacturers stand on chemical treatment
This is the part many websites skip, although it matters. Marley lists a toxic wash as one acceptable way to treat moss and lichen, provided the team protects plants and gutters. It does not name softwash as a product or a method, so we will not claim that it does.
Wienerberger adds a fair caution. Anti-moss treatments are not a permanent solution, and ongoing monitoring and maintenance still matter. As a result, no honest contractor can promise a roof that never grows moss again.
Does the tile type matter?
Yes, and a good operator checks before they start. Clay, concrete and natural slate behave differently, and old tiles are more fragile than new ones. For example, a cracked tile can hide under moss until the water arrives.
- Concrete tiles have a surface layer, so force is the main risk.
- Clay tiles stay damp when moss sits on them, which is why treatment helps.
- Natural slate can turn brittle with age, so nobody should walk on it.
- Old or damaged tiles may already be cracked, so a roofer should look first.
The same logic still applies whether you want roof cleaning in Tunbridge Wells or roof cleaning in Sevenoaks. Both towns have plenty of older homes, so a survey before the work matters even more there.
What can still go wrong with softwash
Softwash is gentle, yet it is not risk free. Four things are worth knowing about, and a careful team plans for each one.
First, a strong mix can mark some materials, such as lead flashings or painted surfaces. Because of that, the team should cover or rinse them. Second, runoff reaches your garden and drains, so plants need watering first and overspray needs rinsing away.
Third, the biocide has to be a legitimate product. The HSE says a biocidal product needs authorisation before anyone can sell it in Great Britain. Since it is your roof, ask for the product name and its data sheet.
Finally, access matters. Even the gentlest chemistry cannot make up for a team that walks on fragile tiles, because a cracked tile lets water in. Our post on whether roof cleaning needs scaffolding explains how crews usually reach a roof safely.
Questions to ask before you book
A short list of questions tells you a lot about a contractor. Vague answers usually mean vague methods, so push for specifics, because good firms welcome questions.
- What product will you use, and at what dilution?
- Will anyone walk on the tiles, and if so, how?
- How will you protect plants, flashings and paintwork?
- What does the guarantee cover, and for how long?
- Can you give me a written, fixed quote after a survey?
For reference, we back our work with a 5-year regrowth protection guarantee. Since roofs differ, we confirm the method once we have seen yours. We can also quote for roof cleaning in Tonbridge, roof cleaning in Dartford or roof cleaning in Chatham.
How long does the result last?
Cleaning is not a one-off cure. We quote that a treatment typically keeps a roof visibly clean for four to five years, although shaded roofs can need attention sooner. Wienerberger advises an annual visual inspection and a closer maintenance visit every three to five years. Our post on how often a roof needs cleaning shows how those timings fit together.
Moss is not always harmful either. Marley says low to moderate growth is a natural part of ageing and not normally harmful to tiles. However, heavy growth is a different matter, and we explain why in whether roof moss harms your house.
Common questions
Will softwash strip the colour from my tiles?
Not at the right strength with a proper rinse, because the force is what removes colour. Colour loss links mostly to high-pressure washing, which Wienerberger says can strip colour from concrete tiles.
Is it safe for my garden and pets?
Plants need protection, and overspray needs rinsing. Meanwhile, keep pets indoors during the work, and follow your contractor’s advice on when the area is safe again.
Can softwash fix a leaking roof?
No. Cleaning removes growth, while a leak points to a damaged tile, a failed flashing or a blocked gutter. A roofer should repair those faults.
Where can I see all of your services?
Our services page lists everything we offer, from roof cleaning to gutter clearance. Because every roof differs, if you are ready to go ahead, you can request a free quote and we will tell you plainly what your roof needs.