The short answer
Zinc and copper strips slow moss growth but do not stop it outright. Rain washes tiny amounts of metal down the slope, which discourages moss and algae below the strip. The effect weakens with distance, depends on regular rainfall, and does little in deep shade or on a roof that is already covered in growth. The roof still needs cleaning first, and occasional checks after.
How a metal strip works on a roof
The idea is simple. A narrow strip of zinc or copper is fixed under or alongside the ridge course, so that part of it is exposed to the weather. When rain falls on the metal, it carries a trace of dissolved metal down over the tiles beneath. Moss and algae do not like it, so they settle less readily on the surface it has washed.
The strip does not coat the roof or kill anything instantly. It works by making the damp surface less welcoming over time, which is why it is described as a deterrent rather than a cure. Copper is generally regarded as the more potent of the two, while zinc is the more usual choice because it is cheaper and gentler on the look of the roof.
Because the effect depends on water running over the metal, a strip needs to sit high on the slope, ideally along the ridge, so that the whole pitch below it gets a wash with every shower.
The limits of strips against moss
Strips have real limits, and it helps to know them before paying for a fit.
They reach only part of the slope
The effect fades with distance from the strip. On a long pitch, the lower courses near the eaves may get too little metal to matter. Roofs with more than one strip, set at intervals, are sometimes used to cover a long run.
They do not remove growth
A strip prevents new colonies more than it clears old ones. A roof already carpeted in moss needs to be cleaned first, or the existing growth simply carries on beneath the metal's reach.
Shade and drainage still win
Where a slope is permanently damp, because of overhanging trees or a north-facing aspect, growth can outpace the metal. We discuss that pattern in why moss grows on one side of a roof.
None of this makes the strip a poor idea. It makes it a helper, not a replacement for upkeep.
Zinc or copper, and what to expect from each
Zinc is the commoner and cheaper strip. It fades to a muted grey with age and sits quietly against most coverings. Copper has a stronger effect on growth but stains lighter materials green and brown as it ages, which is a consideration on pale tiles or stone.
Either way, a strip is a long-lived metal item that needs no maintenance of its own, though it can become dull or coated with debris. If the strip is buried under moss or leaf litter, it cannot shed the water the system depends on, so a brush along the ridge once in a while keeps it working.
On a listed building or inside a conservation area, adding visible metal to a roof is a change in appearance. Ask the planning team at the council before fixing anything, rather than assuming strips are exempt.
Fitting strips and what it adds to the job
A strip is fixed under the edge of the course below the ridge, with the exposed edge showing a short distance. It is quick to do, but it needs access to the top of the roof, so the real cost is often the set-up. Fitting strips during the visit when the roof is cleaned means the platform is already there.
The cost of fitting a strip turns mostly on access and time on the roof, so the figure is agreed after the survey and given in your written quote. What national figures do exist cover the clean itself: MyBuilder's 2026 clean-only figure starts at about £300 for a whole roof and manual scraping at £5 to £10 per m². Our note on access for roof cleaning explains why the scaffold or tower is usually the larger cost.
On tiles that are cracked or brittle, a strip has to be slid under with care. A tile that breaks while we work is swapped for a sound one before the metal goes in, so the strip never sits on a weak course.
Strips, regrowth and a sensible routine
If you are wondering whether strips mean you will never clean the roof again, the honest answer is no. They can lengthen the time between cleans on a roof that has decent light and drainage. Our answer on how quickly roof moss grows back looks at what sets that pace.
A good routine is to clean the roof, fit the strips while it is accessible, trim any overhanging branches and keep the gutters clear. Check the ridge now and then from the ground with binoculars.
If you plan to sell, a tidy, moss-free roof reads well, though strips alone do not change a survey: see roof cleaning before selling.
Questions to settle before you pay for strips
Ask what the roof is made of, which slopes carry the moss, and how much light they get. A sunny south slope with a little growth may not need strips at all. A shaded north pitch may need them and more besides.
You can find our wider advice at roof cleaning and moss removal. Photos of the ridge and the worst slope to 01453 933613 on WhatsApp, and any fitting we do is covered by a 10-year workmanship guarantee in writing.