How often should a house roof be cleaned?

Roof cleaning is one of those jobs with no single right interval, and plenty of roofs get cleaned too often, too roughly, or years too late.

Scott has spent more than 36 years on Surrey roofs and still answers the phone himself, and every job leaves with a 25-year written workmanship guarantee. Whether you need roof cleaning or roof cleaning in Godalming, we cover the whole area.

Ring 07428 300474 for a free survey and an honest answer on whether your roof needs cleaning yet.

How often should a house roof be cleaned?

Most house roofs need cleaning every three to five years, and a shaded, tree-lined or north-facing roof closer to every two to three. Rather than working to a fixed diary date, clean when moss and debris start holding water on the tiles or blocking the gutters, because that is when a roof starts taking damage.

What decides the interval on your own roof

Two houses in the same road can want very different timings. The one under a line of oaks, with the roof facing north and never seeing an afternoon of proper sun, will grow moss steadily and hold damp in the tile surface for days after rain. The one facing south with clear sky above it may look presentable for six or seven years with nothing more than a gutter clear-out.

The things that shorten the interval are the ones you can see from the ground. Overhanging branches drop leaf litter and needles into the valleys and behind the chimney. Shade keeps the tiles damp. Older concrete tiles lose their surface finish over decades and become rougher, so moss takes hold faster than it does on a smooth slate or a newer tile. A shallow pitch drains slowly and gives growth more time to settle in.

Position on the plot matters too. A roof tight against a neighbouring wall, or one sitting in a hollow where air moves slowly, dries out badly. So does anything with a north-east slope in a damp valley bottom, which describes a fair number of houses across Surrey and the Wey Valley. Whether you need roof cleaning or roof cleaning services Guildford, we cover the whole area, and the honest answer changes house by house rather than following a national rule of thumb.

The other quiet factor is what has already been done to the roof. A roof that has been scoured hard in the past, with pressure washing that has stripped the tile surface, will regrow moss far quicker afterwards. That is one of several reasons the work is better done gently the first time.

The signs that tell you it is time, whatever the calendar says

Dates are a rough guide. What actually decides it is the state of the roof, and most of it can be read without going anywhere near a ladder.

• Moss standing proud of the tile edges. A green tint on the surface is cosmetic. Cushions of moss sitting up off the tile, especially along the laps and in the valleys, are holding water against the roof and lifting the tail of the tile above.
• Moss and grit in the gutters. If you are pulling handfuls of dark crumbly debris out of the guttering each autumn, it came off the roof, and there is more still up there.
• Blocked or overflowing downpipes. Water spilling over the gutter front in heavy rain usually means the outlet is packed with roof debris rather than the gutter being wrongly sized.
• Debris in the valleys. Leaf litter dammed in a valley pushes rainwater sideways under the tiles. This is the one that turns into a genuine leak.
• Growth against flashings and around the chimney. Moss packing in behind lead work traps damp exactly where you least want it.
• Moss falling into the garden. Clumps of it coming down on their own after a frost mean the growth is thick enough to lose its grip.

Any of those means it is time, whether the last clean was two years ago or eight. Equally, if the roof is clear and the gutters run free, leaving it alone another couple of years does no harm. There is nothing to be gained from cleaning a roof that does not need cleaning, and we will say so on the survey if that is the position. Whether you need roof cleaning or roof cleaning in Woking, we cover the whole area, and a look before you commit costs nothing.

Why the method changes how long it lasts

How a roof is cleaned has more bearing on the next interval than the cleaning itself. High pressure water blasts moss off quickly and looks impressive for an afternoon. It also drives water up under the laps, strips the factory surface off concrete tiles, dislodges bedding on ridges and hips, and leaves a rougher, more porous tile than it started with. That roof will be green again sooner, and it may leak in the meantime. We soft wash at low pressure and scrape moss off by hand, and we do not pressure wash roofs.

Doing it by hand also means somebody is up there looking properly. Slipped or cracked tiles, tired mortar on the ridge, a flashing that has lifted, a valley that has been quietly overflowing for a year: all of it shows up during a clean, and it is far cheaper to catch than to discover after a ceiling stains. Where fixings or ridge work need attention, they get put back to BS 5534 for fixing and wind uplift, not just bedded down and hoped for.

The same thinking applies to what we do not do. We do not push roof coatings. A coating is sold on the promise of keeping moss away, and on a sound roof it is usually money spent on a problem that a gentle clean every few years handles perfectly well. Our roof cleaning services are built round doing it once, doing it properly, and telling you plainly if a smaller repair is all that is warranted. Every job carries a 25-year written workmanship guarantee, handed over in writing before the team leaves.

Keeping the interval as long as possible in between

A few habits stretch the years between cleans without much effort. Clear the gutters and outlets each autumn once the leaves are down, because a clogged gutter keeps the bottom courses of tile permanently wet and gives moss a footing. Cut back branches that hang over the roof, both for the litter they drop and for the shade they cast. Keep an eye on the roof after storms and after hard frosts, when loose growth and slipped tiles show themselves.

Ventilation is worth a thought as well. A roof that is damp from the inside as well as the outside stays wet longer, so persistent condensation in the loft is worth sorting on its own terms, and BS 5250 covers what good practice looks like there. If your loft feels clammy or you find damp on the underside of the felt, that is a separate conversation from the moss on the outside, but the two are related.

If you are hunting for a roofer close to home in the villages along the Wey, our own local roofers do the work, never subcontracted strangers, and Scott answers the phone himself whatever the hour. Thirty-six years on Surrey roofs tends to make the timing question easy to answer once somebody has actually seen the roof: some houses want a clean every couple of years, some can go a decade, and guessing from the pavement helps nobody.