As a response to one of my posts early this year, someone mentioned their opinion about the damage moss does to your roof:
August 23, 2011 at 1:40 pm (Edit)
“In the information on a first flow diverter, a comment was made that the water came from a composition roof with moss on about 30% of the surface. Any good real estate home inspector will tell you that moss does not grow on a good composition roof; moss requires a degrading surface that allows it to penetrate into the surface and hang on. If good composition roofs are problematic, moss covered ones should be of great concern for slow filter users.”
Moss will grow on any roof if there is enough moisture, and shade; and the moisture it holds is the most destructive part of the situation. Although it is probably a good idea to remove the moss from a roof; the moss, in itself does not “eat away at the roof”. Putting weed killer and moss killer, and pesticide on a lawn, or a roof to make it “look” nice is what is really “bad”. That stuff inevitably makes its way to the lakes, rivers, and oceans of this earth causing tremendous damage. There are contractors who will clean your roof without using toxic chemicals or super-high pressure water.
The moisture that the moss holds may freeze and cause damage to the roofing material by lifting and cracking the tabs on composition roofing. In the Pacific northwest part of Washington state it rarely gets cold enough to be concerned about this problem. Also, the moisture that moss holds can be destructive to the wood in the roof framing. That said, moss is not automatically destructive to all roofing in all cases. To assume that all moss on all roofing material is destructive to the roof by “eating away at the roof” is not the whole story. Moisture and sunlight are the two most destructive elements to be considered. Clogged gutters will cause lots of water damage, particularly if the water freezes under the roofing at the edge along the gutter. Direct sunlight and heat will destroy a roof very quickly. High quality roofing material and proper installation will do more to increase a roof surface longevity that will dumping poisons and other noxious chemicals on poorly installed roofing material or low quality (cheap) roofing material.
Moss is everywhere and is an important part of the ecosystem. As far as roofwater harvesing – moss actually takes nutirients out of water that passes over it – it removes stuff from water helping in the purification process. The links below confirm this.
From Oregon State University: moss does NOT have “roots” it has rhizoids, and they don’t “penetrate”. And furthermore, moss will grow on any compositon roof, degraded or not, if there is enough moisture and no poision, such as zinc or copper strips that are toxic to most plant life.
There are 10,000 species of moss and 7500 species of liverworts (that look like moss) -
Don’t confuse moss and liverworts
Not all moss gets nutrients from the substrate on which it grows. Some mosses get their nutrients from water. The idea that any moss on a roof will “eat away” the roofing is not true.
From Southern Illinois University: At the bottom of the second paragraph:
“Near the base of the shoot, reddish-brown, multicellular rhizoids emerge from the stem to anchor the moss to its substrate. Water and mineral nutrients required for the moss to grow are absorbed, not by the rhizoids,but rather by the thin leaves of the plant as rain water washes through the moss cushion.”
Moss does not extract minerals or food from the stuff it grows on (from: Australian National Botanic Gardens and Australian National Herbarium, Canberra.)