On 3/8/2014 7:31 AM, Stephen Wolstenholme wrote:

It hasn't caused any damage to my roof and it's been growing for about
50 years.

It hasn't damaged my roof, either, but when clumps of it come loose,
they can clog the drains.

It didn't grow on my previous house roof because it was tiled. Some
tiles slipped or blew off occasionally. I can't help but think that
moss holds some roof materials in place.