Cleaning
Moss removal without wrecking the tiles
Moss holds water against the covering, blocks gutters and lifts tile tails in frost. Removing it is worthwhile. Removing it with a pressure washer usually costs more in the long run than leaving it there.
Why pressure washing is usually the wrong tool
A high-pressure lance takes the moss off, and it takes the weathered surface of the tile with it. On concrete tiles that surface is what carries the pigment and much of the water resistance; stripping it leaves a porous tile that holds more water and grows moss back faster.
It also drives water up under the laps, into a roof that was designed to shed water downwards, and it dislodges bedding mortar at ridges and hips.
Scraping and brushing by hand, clearing the gutters afterwards, and treating with an appropriate biocide is slower and does less damage. Where moss keeps returning on a north slope, that is the roof telling you about shade and moisture rather than about the cleaning method.
Be careful about roof coatings
A cleaning quotation that turns into a sealant or coating applied over the whole roof is worth pausing on. Coatings can trap moisture in the tile and can complicate any later repair, and a coating does not fix a roof whose fixings or underlay have failed. Get the condition assessed before agreeing to a treatment.
Roof cleaning questions
Does moss actually damage a roof?
Heavy growth does. It holds water against the covering, blocks gutters and valleys, and in frost the expansion can lift tile tails and loosen bedding. A light growth on a sound roof is cosmetic, and it is fine to leave it.
How long before it grows back?
It depends entirely on the aspect, on overhanging trees and on how porous the covering is. A shaded north slope under a tree will regrow within a few years whatever is applied. That is worth knowing before paying for a treatment sold as permanent.
Not sure what your roof needs?
An inspection ends with a written report and photographs, whether or not you go ahead with the work.
Inspection fee: £99.00.