Moss growth on roof surfaces should be discouraged. I see it all the time when inspecting homes in the Pacific Northwest and call it out on most Home Inspection Reports. The effects of moss on roofs can be devastating, even after a relatively short period of time and allowing it to grow can be an expensive mistake. In fact, most insurance companies will require the removal of moss from roofs.
The problem is that moss will attack and can ruin a composition roof. It can also create dams, causing water to run sideways under your shingles causing a leak. Another issue is that moss can grow under the bottom edge of your shingles thereby pushing the shingles upward, breaking their seals, and rendering the roof more vulnerable to wind damage and wind driven rain. Moss also soaks up water and keeps your roof wet; and, as we all know when most things stay wet for a long period of time, they eventually break down.
Moss has root-like structures called rhizomes which are sent out and embedded into the roofing materials to anchor the moss to the roof. These rhizomes, or roots, supply nutrients for moss (similar to tree roots), but in so anchoring to the roof surface they dislodge the protective granules from the roof surface and expose the roof to further attack by more moss! Left completely unchecked, moss can penetrate all the way through the roofing materials , deteriorating the shingles and obviously rendering the roof surface very vulnerable to leaks.
Moss should be removed quickly before it overtakes your roof to extend the useful life of your roof coverings. Here’s a YouTube Video I created addressing why moss should be removed from your roof surfaces. Please watch the video, Like It, and share or re-blog at will!