I'll be along again in a minute with another question that my son has raised, but here is Q1.
His house is in a large "garden" with huge trees, which drop all sorts of stuff onto his roofs. The north facing parts in particular were holding large quantities of organic debris, moss and so on. He has had the roof cleaned and the broken cement ties replaced where necessary.
The roofing contractor has been advocating fitting a copper ridge cover which, he says, will keep the roof clean for ever and save over the years by vastly reducing roof maintenance. I am very doubtful, as the trees, birds etc. will still drop what they do and, although copper is likely to act as a mild fungicide, I'm not certain it will work. I am also not sure why it won't turn a bright green as in old cathedral roofs.
The south facing roofs have much less tree cover and didn't look as if any cleaning was needed anyway.
Has anyone done this and have any advice?