Toronto Roofing Problem # 2 - Dealing With Growth on Your Roof

Here at Professional Roofers we’ve dealt with all kinds of roofing problems. Homeowners typically expect roof damage from extreme wind or torrential rainstorms: what they often don’t think about are the slow culprits. The common, everyday things that can seriously deteriorate and decrease the lifespan of a roof: I’m talking about moss, lichen, fungus, and blue-green algae.

Most people tend to lump all of these potential growths together as the same thing, but each type is unique in it’s own right and holds its own set of potential problems for your roof. The first thing you need to know if you have discovered a growth on your roof is what it is.


Mosses are small, simple, and flowerless plants – meaning they have roots, stems, and leaves and they photosynthesize (convert the sun’s energy into energy they can use: “food”). If you have moss growing on your roof, you will know because they are the only species in this category that meet the “plant” criteria. Look for tiny leaves, stems and roots – they will be the clear identifier. Mosses tend to thrive in damp or shady locations with lots of debris, and typically grow in large clumps. They retain water on your roof, often reducing its lifespan. Mosses cannot grow on a clean roof, as they require water and some form of debris to grow.


Lichen are considered a composite species – they are actually a mix between algae and fungi. The fungus absorbs nutrients from the air and what the Lichen grows on, while the algae half allows the species to photosynthesize. These species anchor themselves incredibly well to surfaces and are therefore very difficult to remove without damaging your roof. They vary in colour, but will often look like spots on your roof, of varying sizes.


Blue-green algae are actually not blue or green or even algae at all (despite the very confusing name), they are small bacteria called gloecapsa magma. These bacteria feed off of the calcium carbonate in your shingles and prefer warm, moist environments to survive. Since the bacteria are so small, they are easily blown about in the wind, travelling from house to house until they find a suitable place to call home. If you have blue-green algae on your roof, you will see black spots and marks across your roof. Oftentimes, people mistake these stains for oil, dirt, mildew or mould.


Fungus or fungi are a wide-ranging group of organisms. In relation to your roof; however, you will likely see fungi in the form of a black/green slime. This slime is caused from dirty water leaking onto your roof (ex. from a gutter). When this dirty water builds up, it forms a black, decomposing slime and the green part (the fungus) will grow on and around it.



Now that you’re able to identify what is growing on your roof, the next important question you need to ask yourself is what can I do about it? There are many ways to remove these growths; however, much of what you see published online will actually cause more damage to your roof in the process. Here at Professional Roofers, every Toronto roofer on our team is experienced and trained in the best ways to fight and prevent these growths on your roof in a way that will protect, not ruin, your investment.

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