Using a new generation of ‘photo catalytic’ self-cleaning glass is the ultimate in low maintenance technology. Every roof comes with an invisible dual action coating to the outer face, which first acts by using the ultraviolet energy in ordinary daylight to break down organic dirt. Secondly, rather than forming droplets, as the picture shows, water ‘sheets’ down the glass, carrying the dirt away with it.
But does it really work? Well, self-cleaning glass uses daylight and water to power its chemical and physical reaction, the sun providing the light and the rain providing the water. Given these conditions, yes it does really work!

Self cleaning and non self cleaning glass