Roof moss killers compared: Wet & Forget, Jeyes Fluid, bleach and vinegar

The comparison

Wet & Forget

This is the one most people have heard of. Its maker says it works with the rain: rain "works with the formula to gently break down and wash away mould, algae, and lichen over time." It lists terracotta tiles and conservatory roofs among the surfaces it can treat, and advises applying it when "there won't be any rain for at least 4-5 hours".

The catch is time. The maker says you might see results in days on light growth, but that on a heavily mouldy driveway "this can take up to 6 months". On a roof with thick cushions of moss, that means months of moss still holding water and washing into the gutters. Thick moss is better taken off by hand first.

Jeyes Fluid

Jeyes Fluid is a disinfectant and outdoor cleaner, and its label is clear about what it's for: "clear & disinfect paths, patios & driveways from all traces of dirt, mould, algae & fungi stains". Roofs and moss aren't listed.

Two lines on the label matter for anyone thinking of using it on a roof. It says "avoid contact of product with plant life", and it warns that the "formula may stain, soften plastics or discolour brick & paintwork". Many gutters and downpipes are plastic, and everything sprayed on a roof runs into them.

Bleach and vinegar

Neither is made, sold or labelled as a roof moss killer, and the bigger danger is what happens when people combine them. France's national health and safety agency, ANSES, warns that mixing bleach with vinegar or another acid "releases chlorine gas, which is toxic". It recorded a sharp rise in poisonings from home-made weedkillers after some garden herbicides were withdrawn.

The Health and Safety Executive says some home-made remedies fall outside the pesticide rules, but that this doesn't mean they're "without risk or that it is always legal". Whatever you put on a roof ends up in your gutters, your drains and the soil below.

Where the run-off goes

A roof is a big funnel. Everything sprayed on it runs into the gutters, down the downpipes, and either into a soakaway or a drain. HSE tells home users to "never pour PPPs down the drain, toilet or sink" because of "the risk of contaminating water and harming wildlife", and spraying a roof sends product the same way.

Marley, one of the UK's biggest tile makers, warns that chemical washes "can be harmful to plants and animals" and that gutters and outlets should be protected. On Mumsnet, one homeowner found that after a roof treatment "the spray and splashes killed all my plants on that side of my garden."

That old bottle in the shed

Pesticide approvals change. HSE's advice is to check its database before using any product you already have: "If the product is not listed on the database it's probably no longer authorised and so will be illegal to use." Read the label before you buy, and again before you use it.

Do moss killers work for long?

Less than most people expect. Historic England's research on biological growth found that the performance and longer-term effectiveness of common biocides "has been observed to be extremely limited", and that some stopped working after about three months. The RHS notes that most moss and algae products don't persist, so they need repeating.

A treatment is useful after the moss has been removed, to slow regrowth. It isn't a substitute for taking the moss off.

What we use

We take the moss off by hand first. Where it suits the roof, we follow up with an approved professional moss and algae treatment, used exactly as its label says, sprayed at low pressure and kept off plants, ponds and painted or rendered walls. Then we clear the gutters of everything that's come down.

Written by Hawkes Roofing, roofers based in St Albans who remove roof moss by hand across Hertfordshire, Buckinghamshire and north-west London. Last reviewed 26 October 2026.