Two quotes for the same roof commonly differ by a factor of two or three, which makes homeowners assume someone is overcharging. Usually nobody is: they are quoting different work. This explains what varies, so you can tell which.
Why there are no prices on this page
Because we would have to make them up. Every roof is priced on access, size, pitch, tile type and how far the growth has gone, and a range printed on a web page for a roof nobody has seen is marketing rather than information. If the number were reliable, nobody would need to send photographs.
We would rather give you the variables and quote your actual roof. Send a photo and the quote is free and specific, which is worth more than a range you cannot rely on.
What actually moves the price
Access, more than anything else. This is the single biggest variable and the one homeowners least expect. A bungalow that can be treated with long-reach equipment from the ground and a three-storey roof over a conservatory are the same cleaning and completely different jobs. If a tower is needed, that is equipment, time and a second pair of hands before any cleaning happens. Whether a van can park within hose distance matters more than it sounds.
Size and pitch. Area is obvious. Pitch is less so: a steep roof takes longer to treat evenly, and a shallow roof holds water and growth for longer, so the two cost more for opposite reasons. Roof shape matters too — dormers, valleys and multiple pitches take far longer than one large plain rectangle of the same area.
Tile type. Concrete interlocking tiles are the straightforward case. Slate needs more care and cannot be walked on at all. Clay varies with age. Fibre cement may be too fragile to clean at any price. The material decides the method, and the method decides the time.
How far the growth has gone. A light algae film is a treatment. Thick moss with a build-up at the ridge and in the valleys is a physical removal job first, and the volume of material coming off changes both the labour and the clearing up.
Whether a biocide treatment is included. Frequently the real reason two quotes differ. Removal alone is cheaper and the growth returns sooner. Removal plus treatment costs more and lasts considerably longer. Both are legitimate; they are just not the same purchase.
What happens to the gutters. Everything taken off a roof lands in them, so clearing afterwards should be part of the job. If it is not in the quote, it is either an extra or it is not happening — and a roof cleaned over blocked gutters has swapped a cosmetic problem for a damp one.
Comparing two quotes
Get both in writing and check they describe the same work. Specifically, whether each one includes the treatment, the gutter clear, the access equipment, and what happens to the debris. A quote that is a single number with no method named is not comparable to anything.
Be wary of a quote given over the phone without photographs or a visit. Access is the biggest cost driver and it cannot be assessed from a postcode, so a firm price offered before anyone has seen the building is either padded to cover the worst case or about to be revised upwards on the day.
Be equally wary of a quote that is far below the others. In this trade the cheapest quote is very often a pressure wash where soft washing was needed, which is faster, cheaper, and takes years off the roof.
When it is not worth doing
A roof within a few years of replacement gains very little from being cleaned, and the money is better kept towards the replacement. A roof with cracked, slipped or delaminating tiles needs repair first — cleaning will find every existing weakness, which is a useful survey and an expensive way to get one.
And if the actual problem is that moss is shedding into gutters that overflow, the gutters are the job that needs doing. It is a fraction of the cost, and it addresses the thing that is doing damage rather than the thing that looks untidy.
Where cleaning is worth doing, how we do it sets out the method and what it involves.