In article ,
marvelus writes:
On Fri, 6 Oct 2006 13:42:35 +0100, "Andrew Mawson"
wrote:

However if you can get someone to install a thin taut bare copper wire
either side of the ridge, rain (which is slightly acidic) will form
copper salts which washing down the roof will kill the lichen

This is a myth.

Nope. There was a brilliant example next door to my grand parents.
Their bare phone wires passed over the roof of next door bungalow.
There was a very straight line across the roof some ~5' under the
phone wires were any drips would land. From that line all the way
down the the gutter, the roof was completely clear of moss and lichen.
Above that line, it was covered in both. That was the first time I
noticed the effect, long before I ever read or heard about it
anywhere else.

--
Andrew Gabriel