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How to Prevent Moss Growth on Your Roof

Moss covering asphalt roof shingles

It is said that there are only two sure things in life: death and taxes. While we are great roofers, and not so great philosophers, we would like to add one more thing to that list, at least for Toronto homes that have asphalt shingle roofs.

Algae, Moss and Fungus Growth on Your Roof

You don’t often replace the roof on your home and when you do it’s always rewarding to see the house with the nice new shingles on top. But, within just a few years, those shingles that still have at least 15 years to go on their warranty can be discoloured by green, brown or gray growths of algae, fungus or moss.

Not only can the growth be harmful to you or your roof, it can make your home look older and reduce its resale value if you put it on the market.

But, if you do have vegetation growth on your roof, check below the metal flashing at the bottom of your chimney or around attic vents. Hmm …. there’s no growth there. And that’s your clue for how to prevent all vegetation growth on the roof.

The absence of growth below metal flashing is due to the fact that the copper and zinc used to coat the flashing are toxic to algae, moss and fungi. It’s also one of the reasons why you won’t see them growing on copper roofing.

Two Ways to Prevent Vegetation Growth on Roofs

1. Growth Resistant Shingles

Many roofing material manufacturers now offer asphalt shingles that include copper granules in the protective granular coating.

2. Shingle Shields

if your current roof is free of growth, or you’re installing a new roof, adding a Shingle Shield near the ridge line of your roof will prevent algae, moss and fungus from growing. As rain falls across the Shingle Shield, it carries zinc oxide from the strip across your roof.

So now we can return the list of ‘the only things in life that are sure” to just two items.

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