The short answer
It can. Cleaning removes the growth that is there, but the moss can come back wherever shade and damp linger and the tile face is rough. A thorough treatment of the roots slows regrowth, and trimming trees and keeping gutters clear helps more. No honest roofer can promise moss will never come back, so the aim is to lengthen the gap, not to end it.
Moss follows moisture. Clean a roof and the cause stays on site, so the realistic goal is a longer gap between cleans.
Why moss returns
Moss spreads by spores, which are tiny and carried on the wind. They land on every roof. Whether they take hold depends on the conditions they land in, and a cleaned roof in a damp, shaded spot offers the same conditions as before.
What does moss need to come back?
Moisture first, then a surface to grip, then time. Shade from walls, trees or a neighbouring building keeps tiles wet for longer after rain. Leaves, grit and old moss lodged in gutters, and in the valleys where two slopes join, hold water against the roof for days after the rain has stopped. A tile that stays wet gives spores the best chance to settle. A worn or rough tile face gives roots a foothold that a smooth, intact face does not.
That is why a roof can look clear for years in one place and green again within a couple of seasons in another. The cleaning itself is not at fault. The surroundings decide, and our answer on moss on the north side of a roof shows how strongly shade shapes where growth appears first.
What slows it down
Several things push the gap longer, and the best results come from combining them rather than relying on one.
Does the cleaning method make a difference?
Yes. A method that only strips the surface leaves roots and spores in the tile face, so regrowth starts from what remains. A biocide treatment, applied as its label directs, reaches the living growth, which is why it generally holds longer than scraping alone. Marley does not recommend jet washing, and roughening a tile makes regrowth easier, so gentle methods suit this goal. Our page on soft-wash roof cleaning describes one.
Beyond the method, the surroundings matter. Cutting back overhanging branches lets in light and wind. Clearing gutters and valleys of leaves removes the damp pockets where moss restarts. Some owners fit metal strips along the ridge so rainwater washes over the roof, which our page on zinc strips and roof moss covers. None of these is a promise, but together they lengthen the time before the next visit.
What to expect after the visit
Right after a treatment the roof may look much as it did. The growth is dead but still attached, and the weather takes weeks to shift it. Judge the result then, and do not read a patchy first fortnight as failure.
How will I know if moss is returning?
Look at the places it started before: the shaded slope, the lower edge near the gutter and around chimneys. New growth shows first as a fine green fuzz or a dark film rather than the thick cushions you saw originally. Spotting it at that stage is useful, because a light return is a small job, where a mat is a big one, and the roof beneath stays in better shape. A phone photo with the date on it settles any doubt about whether the patch has grown.
Photograph the roof from a couple of fixed corners of the garden after the clean, then repeat each spring. They show whether growth is creeping back and how quickly. If it returns faster than you expect, the cause is usually a trapped patch of damp, such as a blocked gutter or an overhanging branch, and fixing that matters more than cleaning again. We look for those causes when we survey, and the photos we take of your roof show them.
Planning for the long run
A sensible plan accepts that moss is a recurring job on some roofs and a rare one on others. The aim is to keep it at the level where it does no harm: thin, dry and not holding water against the tiles.
Is it worth cleaning if moss will return?
Often yes, because thick moss is the problem and a light film is not. Removing a deep mat takes weight and moisture off the tiles and clears the gutters. If you want to weigh the case, our page on roof cleaning and moss removal covers the methods and when each suits.
Where the covering is already failing, cleaning is the wrong spend. A cracked tile, or a soft batten (the timber strip that carries the tiles), needs mending whether or not moss returns. Have us survey the roof, look through the pictures taken of your slopes, then choose between a clean, a repair or both when the single written price arrives. That way the money goes where the roof needs it, and the regrowth question is answered for your house, not for an average one.
More on moss regrowth
How soon might moss show again after a clean?
It depends on shade, damp and the method used, so no timescale is dependable. A shaded slope with overhanging trees can show fresh growth sooner than an open, sunny one. Check the problem areas each spring with photos. A light return is easy to treat before it builds up into a mat.
Does a coating stop moss growing back?
A coating is not a guarantee against regrowth, and it only suits clean, sound tiles. Some owners choose one for appearance. Whether any product helps depends on the product and the conditions, so ask what the maker says about moss on that surface and keep the data sheet. A coating also adds a layer to look after later.
The full picture: Roof cleaning and moss removal in Taunton ยท More short answers