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 house altogether.
While early bryophytic (mossy) growths are not immediately harmful to roofs, the mature bryophytes can severely damage your roof and really limit 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 rain and coniferous debris. The combination of rain and slightly acidic conditions creates a perfect breeding ground for moss everywhere in BC, including your roof.
Why is moss damaging to my roof?
Mature moss rhizoids (roots) can dig deep into your shingles creating microscopic holes (holes = leaks!).
The flow of water is impeded on mossy roofs allowing water to stand for extended periods.
Moisture is an enemy of buildings. Shingles are specially designed to direct water away from the house. When the roof flow is disrupted, water can enter and accumulate, which can lead to costly premature roof and fascia board replacements.
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 gentle alkaline products like sodium bicarbonate.
Glime, J. M. 2017. Construction. Chapt. 5. In: Glime, J. M. Bryophyte Ecology. Volume 2. pg. 5-1-29.