It roots in dust so you have to get up there and scrap it off or blast with jet spray but only do this DOWN not UP or you'll flood the loft/attic. jSo you need a scafold and roof ladder. Just done my bungalow roof tried all the sprays no good still had to scrap off and clean with jet spray. One tip block off the gutter outlets with wire ball sold for this purpose or you have blocked downpipes if you clean off with jet spray.
Bob
October 2010
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