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How to Differentiate Mold From Algae on Your Roof

Looking up, you see dark stains, black streaks on your roof. Are those algae or mold? How can you tell the difference? The top siding contractor in the area, A Cut Above Exteriors, talks about the differences between the two.

How to Differentiate Mold From Algae on Your Roof


Algae may look like mold, but it’s less threatening. Algae is simply a moss-like plant that grows due to humidity. Algae stains are no threat to anyone’s health and will not cause damage to your roof. It’s just simply unattractive.

Though it’s not damaging and isn’t a health hazard, it certainly can hurt the resale value of your home, simply because a fresh, clean roof immensely boosts curb appeal.


While mold is not nearly as common on roofs than algae, it is the complete opposite of the latter. Mold typically forms in damp, warm, and poorly ventilated areas, like the attic and basement, and can spread to your roof and siding. On top of it all, mold can cause health problems, from asthma and irritated eyes and throat to lung issues.

The easiest way to deal with mold and algae is to prevent them from spreading with regular house and roof cleaning or ventilating your attic. In a worse-case case scenario, you might need roof and siding replacement if the damage from algae or mold stains has escalated.

As the area’s siding replacement leader, A Cut Above Exteriors offers several high-quality siding options, chosen for their suitability to the area’s wet and sunny climate. Homeowners turn to A Cut Above for our expertise in roof and siding services. Our James Hardie® fiber cement siding is durable, energy-efficient, long-lasting, and attractive.

A Cut Above Exteriors is the company local homeowners call for their siding installation and home exterior needs. You can reach us at (503) 334-0733 or by filling out this form and requesting a free estimate. We serve homeowners in Portland, OR.

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Category: Roofing