Mossy Roofs

We all love the look of a green property, well-kept and teeming with life. How about on roofs? Bio-roofs are a prominent feature of some newly constructed high-rises and condos, blending nature with modernity. But mosses should be excluded from your shingles altogether.

While early bryophytic (mossy) growths are not immediately harmful to roofs, the mature bryophytes can severely damage your roof and significantly reduce its lifespan.

Why does moss grow on roofs?

Moss grows on moist, shaded areas in acidic substrates like soil with nearby coniferous trees. In the Pacific North West, roofs take a pounding from acidic rain. The combination of rain accumulating in micro-structures of your shingles and the abundance of bryophytes around Vancouver creates a perfect breeding ground for moss.  

Why is moss damaging to my roof?

Moisture is the enemy of construction. Shingles are specially designed to direct water away from vital structures like the fascia and soffit. When the shingles are disrupted, water can enter and accumulate in these structures and cause significant damage can quickly result in premature roof replacements. Moss disrupts shingling and impedes the flow of water away from vital structures all while retaining moisture.

How do I get moss off my roof?

There are numerous chemical and physical methods that can be effective at removing moss from shingles. Methods like zinc sulfate and iron sulfate applications are highly effective at eliminating moss but will leave a noticeable stain and are extremely toxic to aquatic life. Avoid these types of applications altogether. A preferred method is to gently brush away the bulk of moss and apply a generous amount of alkaline calcium products like calcium carbonate.

Glime, J. M. 2017. Construction. Chapt. 5. In: Glime, J. M. Bryophyte Ecology. Volume 2. pg. 5-1-29.