It can’t be any clearer. I was on a roof in Vancouver, out by The University of BC. We were adding an emergency overflow roof scupper drain and I looked at the asphalt laminate shingle roofs that were surrounding me. What I saw was quite dramatic. The south face of the shingle roof was clean and looked almost new. The north face was littered with moss. I couldn’t believe it. What a contrast. Night and day. Good and bad. Now I have proof!