How To Clean A Tiled Roof
Moss and algae come off roof tiles safely with a scraper and a soft wash rather than a jet wash that chips the surface.
The short answer
To clean a tiled roof, get safe access with a scaffold tower, scrape off the moss with a trowel or stiff brush on a dry day, then soft wash the tiles with a roof cleaning product applied through a water-fed brush at low pressure. Avoid pressure washing, as it chips the tile surface, can dislodge tiles and leaves spores behind to regrow.
Every roof picks up some moss, but tiled roofs collect more moss, algae and grime than most, particularly the concrete tiles found on so many UK homes. Left alone, that growth spoils the look of the house and can start to damage the roof itself.
Cleaning roof tiles isn't a complicated job, and plenty of companies offer it if you'd rather not go up yourself. Either way, the method matters. A soft brush and a low-pressure wash clean the tiles without harming them, while a jet wash does more damage than good. Below we walk through the gentle method step by step, then explain why we'd keep the pressure washer on the ground.
Why Moss And Algae Need Clearing From Roof Tiles
Extra Weight On The Roof
Moss soaks up rain like a sponge. A thick covering across a whole roof holds a surprising amount of water, and that weight puts extra load on the roof structure every time it rains.
Moisture Held Against The Tiles
Because moss stays wet, the tiles beneath it stay damp for far longer than they should. Over time that moisture can work through to the timbers, leading to rotten rafters and damp in the loft, both of which are expensive to put right.
Damage To The Joints Between Tiles
Moss grows best on concrete, so it takes hold first along the edges and joints where the tiles overlap, as the close-up below shows. As it keeps growing, it can push into those joints and break them, which opens the roof up to further damage.
Blocked Drainage And Gutters
Moss in the joints also sits in the path rainwater takes off the roof, so water backs up and stands on the tiles instead of running away. Lumps of moss break off and wash into the gutters too, where they block the outlets and cause overflows down the walls.
A Hotter Loft In Summer
In warm weather, a layer of moss, algae and dirt stops heat escaping from the roof. The loft space underneath gets uncomfortably hot as a result.
Kerb Appeal
For most homeowners, the look of the roof is what prompts the job in the first place. A green, streaky roof makes the whole house look neglected, and if you're selling, it's one of the first things buyers notice from the street.
How To Clean A Tiled Roof Step By Step
Cleaning a roof means working at height, so think carefully before going up yourself. If you're not comfortable on a scaffold tower or don't have the right access kit, a roof cleaning company that uses the soft wash method is the safer choice.
Set Up Safe Access
Getting onto the roof safely comes before anything else. There are several ways to do it, but most roof cleaning companies use a mobile scaffold tower that can be moved along the house as the job progresses, as in the photos below. A tower gives you a stable platform at gutter height, so you can reach up the roof with long-handled tools instead of walking on the tiles.
While you're setting up, cover any plants beneath the eaves and make a note of where the downpipes discharge, as moss and cleaning solution will come down them.
Scrape Off The Moss And Dirt
With safe access to the whole roof, start by removing the moss, algae and dirt by hand. A trowel or a stiff brush is the most effective tool, scraping the growth off each tile and out of the joints. Pick a dry day for this stage. Dry moss lifts away easily, while wet moss clings to the tiles and smears.
Soft Wash The Tiles
Once the loose growth is off, the tiles are ready for a soft wash. Soft washing means putting a roof cleaning product on at low pressure, so it kills the moss, algae and other growth on the tiles without blasting the surface.
The product goes on through a telescopic water-fed brush that gently scrubs the tiles as it washes them. Because the formula includes a fungicide, it carries on working after the job is done and keeps the roof cleaner for longer than water alone.
Clear The Gutters
Finish by scooping the moss and debris out of the gutters and flushing the downpipes through with water. Anything left behind will block them at the next heavy downpour.
Should You Pressure Wash Your Roof
A pressure washer for outdoor cleaning is brilliant on hard surfaces, and few jobs are as satisfying as jet washing patio slabs back to their original colour. A roof is a different matter. Plenty of people still jet wash their own roofs or pay a company to do it, but the reasons below are why we'd steer well clear.
It Damages The Tile Surface
The biggest problem is what high-pressure water does to the tiles themselves. It chips and strips the surface, so while the roof looks cleaner afterwards, the tiles are left rougher and more porous, with a shorter lifespan than before.
Your Tile Warranty Can Suffer
Because jet washing can damage the surface, it can also put a tile warranty at risk. Roof tile maker Marley says on its advice page on cleaning and jet washing roofs that it doesn't recommend jet washing its tiles, so check with your tile manufacturer before anyone gets the pressure washer out.
It Only Shifts Surface Dirt
A jet wash blasts off what you can see, but it leaves the algae and lichen spores that sit beneath and between the tiles. Those spores recolonise the roof, and the rougher, damaged surface gives them even more to cling to. A soft wash with a fungicidal cleaner treats the growth rather than just moving it.
Tiles Can Be Dislodged
Jet washing a roof means putting your weight on the roof, from a roof ladder or on the tiles themselves, while firing high-pressure water at them, as in the photo below. Between the weight of the person and the force of the spray, tiles can lift, crack or slip out of position.
Water Can Get Into The Loft
Once tiles have shifted, water from the lance can be driven up and under them and into the loft. If any tiles aren't put back exactly where they should be, the roof can carry on leaking long after the job, leading to damp in the roof space.
Debris Ends Up Everywhere
As with pressure washing block paving, jet washing a roof sends debris everywhere. Moss, algae and grit end up all over the driveway, patio and windows, and on a windy day a good amount of it lands in the neighbour's garden too.
Keeping A Tiled Roof Clean For Longer
Plenty of companies offer roof pressure washing, but scraping and soft washing is safer for the roof and does a better job of keeping growth away. Once the roof is clean, cutting back overhanging branches lets more sun and air reach the tiles, which slows moss down, and clearing the gutters each autumn stops fallen moss building up.
The same gentle approach works lower down the house. A water-fed pole from our pick of the best water fed window cleaning kits is handy for fascias and soffits after a roof clean, and our guide to removing green algae from a fence covers the same growth on garden timber.
More Questions Answered
Is it safe to clean your own roof?
Cleaning your own roof is safe only if you have proper access equipment, such as a scaffold tower, and you're confident working at height. Never lean a ladder against the gutters or walk on wet, mossy tiles, as they're extremely slippery. If you have any doubts, hire a roof cleaning company that uses the soft wash method rather than a jet wash.
What is the best time of year to clean a tiled roof?
The best time to clean a tiled roof is a dry spell in late spring or early autumn, when it's mild enough for the cleaning product to work and dry enough for the moss to scrape off easily. Avoid frosty weather and wet days, as wet moss clings to the tiles and the roof surface is far more slippery to work around.
Can you use bleach to clean roof tiles?
Household bleach isn't a good choice for roof tiles. It can discolour the tiles, harm plants and lawns where it runs off, and damage gutters and nearby surfaces. A cleaning product made specifically for roofs, applied as a soft wash, kills moss and algae without those problems and leaves a fungicide behind that slows regrowth.
How often should a tiled roof be cleaned?
The gap between roof cleans depends on how much shade and moisture it gets. A roof under trees or facing north greens over much faster than an open, sunny one. Check it each year when you clear the gutters, and clean it when moss starts building up along the tile joints rather than waiting for a thick covering.
Is jet washing a roof really that bad if it looks cleaner afterwards?
Yes, because a jet wash chips and strips the tile surface, so the roof looks cleaner but the tiles are left rougher and more porous, with a shorter lifespan. It also leaves the algae and lichen spores behind to regrow. Marley says it doesn't recommend jet washing its tiles, so check your tile manufacturer's advice and warranty first.
Do I need a scaffold tower to clean a tiled roof?
A scaffold tower is how most roof cleaning companies get safe access, and we'd use one too. It gives you a stable platform at gutter height, so you can reach up the roof with long-handled tools instead of walking on the tiles. If you aren't comfortable on a tower or don't have the right access kit, use a soft wash roof cleaning company.
Why scrape the moss off before soft washing the tiles?
Scraping removes the bulk of the moss, algae and dirt by hand, so the soft wash only has to treat what's left. Use a trowel or stiff brush on a dry day, because dry moss lifts away easily while wet moss clings to the tiles and smears. The fungicide in the soft wash then keeps working after the job is done.
What should I do about the gutters after cleaning the roof?
Scoop the moss and debris out of the gutters and flush the downpipes through with water straight after the roof is done. Anything left behind blocks them at the next heavy downpour. Before you start, cover plants beneath the eaves and note where the downpipes discharge, as moss and cleaning solution come down them.
Richard has spent years renovating properties and turning them into rentals and Airbnbs. Like a lot of people he started out as a beginner, and these days there isn't much DIY he won't take on.