Roof Cleaning

I don't think you're going to get much help unless you tell people a bit more information:

ie: My roof is flat/pitched/etc and made of thatch/slate/concrete tile/corrugated iron/asbestos sheet/etc and by grubby I mean..

;-)

A quick search on the archives for this newsgroup for roof and moss will yield lots of advice.

I would leave well alone. If the moss was excessive and causing blocked gutters and downpipes that needed frequent unblocking then it MIGHT be worth doing something about it. The problem would be finding a reputable firm that wouldn't rip you off or damage your roof.

Fellow near us had his roof pressure washed. He had Marley type concrete tiles and the pressure washing removed much of the coloured coating from them with the consequence that his roof now has a Mediterranean "sun-bleached appearance totally out of kilter with his neighbours roofs. I don't know if there has been any effect on the impermeability of the tiles or of their ability to shed water but it looks a real pig's ear to me.