The risk is the height, not the moss
A wet roof is slippery. Moss, algae and lichen make tiles and slates slick, damp slates can slide on the batten and a tile that looks fixed may be loose under your boot. A pitched roof gives no flat place to rest, and the edge is where a mistake ends.
The law treats working at height seriously. Regulation 6(3) of the Work at Height Regulations 2005 makes employers responsible for stopping anyone falling far enough to be hurt, using measures that are suitable and sufficient so far as is reasonably practicable. That duty lands on employers, so a roofing firm has to plan how its people are kept from falling. A householder who goes up alone has none of that planning behind them.
The ladder is a hazard of its own. The foot may sink into a lawn or slide on a wet patio, the top may rest against a gutter that bends, and reaching sideways to brush a patch shifts the weight beyond the rails.
None of this is about skill with a brush. It is about whether a fall would have anything to stop it.
Checks that need no ladder
Plenty of useful checking needs no ladder and no climb. A householder can:
- look at the slopes from the garden and the street with binoculars, noting slipped tiles, gaps at the ridge and moss thick along the lower edge;
- walk round after heavy rain to see whether a gutter is overflowing or a downpipe is wet at the joints;
- clear leaves from low gutters with a long-reach tool, standing on the ground;
- take dated photographs, which help a roofer understand what has changed;
- check the loft with a torch for damp patches, daylight at the slope or stained rafters.
Moss itself rarely needs an emergency. It is slow, and a few weeks' wait to do the job properly costs little. A leak, a slipped slate or a blocked gutter is different, because water getting in does its damage steadily.
If moss is falling into the gutters, our page on moss blocking gutters explains what happens when it builds up. Keep that watching brief going through the seasons, because a roof that is checked a few times a year gives a roofer something far more useful than a single rushed look.
Products to leave on the shelf
Garden centres sell moss killers made for lawns, patios and paths, and the label tells you what each is meant for. A roof is not on that list unless the label says so. Follow the directions printed on the container, and never mix products or make one stronger than the instructions allow.
Some chemicals sold only to the trade, or sold as concentrates, are a bad choice for anyone without training and the right clothing. Splashes harm eyes and skin, and fumes in a confined space are a risk of their own. Run-off matters too, since it ends up in gutters, drains and a garden, and in a pond if the downpipe runs to a soakaway nearby.
Bleach and household cleaners are no better. They can stain tiles, damage metal flashings and run onto plants and paving below.
The point is not that cleaning products are forbidden, but that a product sold for a roof has a label that tells you how to use it. If the label is missing, or it asks for equipment you do not have, treat the work as one for a professional. Our guide to roof moss removal methods sets out what a trained firm does instead.
When to call a roofer
Call a roofer when anything on the slope itself needs doing, and certainly if you can see damage as well as moss. The signs that make it worth a visit include slipped or cracked tiles, lifted ridge tiles, moss packed between tile laps, daylight in the loft and damp on a ceiling below the roof.
A roofer brings access equipment, such as scaffold, a roof ladder or a tower, along with a method that suits the covering. They can also see whether the moss is hiding something. A tile held in place by moss alone, for example, will fall as soon as the moss is removed, so a clean should be paired with a repair.
Ask for the survey first. Before anything is priced, the roof is looked at, and the roofer should say whether cleaning is worth doing at all or a repair should come first. One written price follows, with the access included.
If the roof is a flat one, a conservatory or an old garage sheet roof, the safe answer is different again: nobody should walk on a conservatory or a cement sheet roof, and a flat roof only once someone knows it will carry the weight. See roof cleaning and moss removal for how we approach each kind.
