Roof Moss Treatment: What Works and How Long It Lasts

Removal and treatment are different jobs

Moss on a roof has two parts: the visible cushions sitting on the tiles, and the spores and fine roots left in the surface. Taking the cushions off improves the look and stops them washing into gutters. Treating the surface deals with what remains, so new growth is slower to return.

A method that does only one of these usually disappoints. Spraying a thick carpet of moss leaves dead clumps clogging the gutters. Scraping without treatment leaves spores ready to regrow.

What we use

Our approach is hand moss removal followed, where suitable for the roof, by a soft wash and biocide. It covers both parts of the problem without pressure washing the tiles, which we never do.

The biocide is applied at low pressure and keeps working after we leave. Lichen and algae often fade gradually as rain rinses them away.

Do shop-bought moss killers work?

Some do kill moss and algae on contact, but they are designed to be applied by someone at roof height, which is where the real risk lies. Ladders on a pitched roof are one of the most common causes of serious falls at home.

Spraying from the ground rarely gives even coverage, and without removal the dead moss stays put until it rots and slides into the gutters.

Zinc and copper strips

Metal strips fitted near the ridge release traces of metal when it rains, which can slow growth below them. Results vary with roof pitch, rainfall and how far the water spreads. They are a preventative idea, not a way to remove moss that is already established.

How long does a moss treatment last?

There is no fixed figure because the main drivers are outside anyone's control. North-facing slopes, roofs under trees and houses in damp valleys regrow faster than sunny, open roofs.

What you can expect is a noticeably slower return than after removal alone, because the surface spores have been dealt with. Keeping gutters clear and trimming branches that drip on the roof both help.

When to re-treat

Rather than booking on a timetable, look at the roof each spring and autumn from the ground. Small green spots along the tile edges are the first sign. Treating at that stage is quicker than waiting for thick cushions to form again.

Our guide on how long roof cleaning lasts covers the factors in more depth.

Treatment on different roof types

Concrete tiles usually carry the heaviest moss and benefit most from removal plus treatment. Clay tiles tend to hold moss in their joints and textured faces. Slate grows less moss but more lichen along the overlaps. The treatment principle is the same on each, but how much hand removal is needed, and how carefully the roof must be walked, varies from one material to the next.

Signs a previous treatment did not work

If a roof greened over again within a short time, the usual reasons are that thick moss was sprayed but never removed, the roof was jet washed and left rough, or nothing was done about overhanging trees. Telling us what was done before helps us plan a better result this time.

Treatment and the gutters

Whatever treatment is used, the gutters below a mossy roof deserve attention. Moss removed by hand is cleared from them on the day, and a final flow test confirms the outlets are open before we leave.

Book a treatment quote

If you would like moss removed and the roof treated, send us your address and a photo. Quotes are free, and we cover Hampshire, Surrey and Sussex.