Been no posts on the general cleaning section for a couple of weeks - less people doing that sort of work and then you have to suffer the little posse who take the moniker of " clean it up god " too seriously
anyways......
the best alternative to not getting on a roof is you use high access equipment - there are a number of smaller 'spider' machines that can fit just about anywhere so the clean the roof from above ( correct procedure )
what you have seen is soft washing there are several companies promoting this however the soft wash chemical is only effective on very light moss - algae - lichen when you start investigating they recommend to scrap off the moss before treating so your back to square one
also with soft washing you will need to explain that it can take upto 8 weeks for the organic material to die off and then you are still relying on rain to wash it off the surface of the roof
Darran