How to remove moss from a roof

Before covering the methods themselves, the single most important safety point must be stated clearly. Never climb onto a pitched roof to remove moss yourself unless you have proper safety equipment including a harness, anchor points and appropriate footwear. Roof falls cause serious injuries and fatalities in the UK every year. A wet pitched roof, especially one covered in moss, is among the most hazardous surfaces a person can attempt to walk on without professional equipment. The good news is that most roof moss removal can be carried out effectively from a ladder, a mobile tower or from the ground using extended-reach tools, without stepping onto the roof surface at all. Professional contractors work this way as standard practice.

Manual removal using extended-reach tools

For light to moderate moss coverage, manual removal using a stiff plastic scraper or brush on a carbon fibre extendable pole is effective and carries no risk of tile damage from water pressure. Professional contractors use tile scraper attachments with reversible wire brushes fixed to carbon fibre poles that reach the full slope of the roof from a ladder or mobile tower, removing bulk moss without anyone stepping on the tile surface. Working from the ridge downward toward the eaves is essential. Brushing upward pushes the scraper or brush under the leading edge of the tile above, which can lift fragile tiles from their nibs or crack thin clay tiles. Always work downhill so that the scraped moss falls freely rather than being pushed back under tile overlaps.

After manual removal, clear all moss from the gutters immediately as the dislodged material will otherwise block the downpipes during the next rainfall. Manual removal alone leaves the tile surface contaminated with moss spores and root systems. Without a biocidal treatment after removal, regrowth begins within weeks. For best long-term results, manual removal of bulk growth should be followed by a biocidal softwash application.

Biocidal softwashing

Biocidal softwashing is the preferred professional method for most residential roofs in the UK and is endorsed by the National Federation of Roofing Contractors. A biodegradable biocidal solution is applied at low pressure (equivalent to garden hose pressure) across the entire roof surface. The chemical penetrates the moss, algae and lichen and kills the organisms at a cellular level. Dead growth then detaches from the tile surface naturally over the following weeks, weathered away by rain and wind. The key advantage over manual removal alone is that softwashing kills the spores embedded in the tile surface, significantly delaying regrowth. A post-treatment biocide application after the initial wash extends the clean period to approximately 2 to 3 years. Softwashing is safe for all common UK residential tile types including clay, concrete and natural slate.

DOFF steam cleaning

DOFF steam cleaning uses superheated steam at very low pressure to kill and remove biological growth from tile surfaces. It is particularly appropriate for heritage properties, listed buildings and roofs with fragile or very old tiles where any chemical application requires specialist consideration, or where an immediate visual clean result is required on the day of treatment. DOFF kills moss, algae and lichen on contact through heat rather than chemistry. It leaves no chemical residue. It is gentle in terms of mechanical pressure but highly effective at biological growth removal. Feel the Pressure UK, a specialist London and Home Counties roof cleaning contractor, describes DOFF as the safest option for slate roofs on Victorian and Edwardian properties.

Methods to avoid when removing roof moss

High-pressure washing is the method most frequently cited as causing damage to roof tiles during cleaning. The National Federation of Roofing Contractors is explicit in its position against aggressive high-pressure moss removal. Pressure washing on clay or natural slate tiles can crack fragile tile material, dislodge tiles from their fixings, erode the cement from ridge mortar joints and force water under tiles into the roof space. Even on concrete tiles, excessive pressure strips the surface protection and accelerates future weathering. Aggressive brushing across the grain or direction of the tile with a metal brush carries similar risk. Vinegar and domestic bleach are sometimes suggested as DIY moss treatments. While diluted bleach can kill moss, it also risks bleaching or staining the tile surface unevenly and can damage surrounding vegetation through runoff. These products lack the biocidal residual protection provided by specialist roof biocides and are not the professional choice for residential roof moss removal.