Dealing with Roof Algae Buildup

by James Florence

When it comes to roofing, most Bay Area homeowners try to get the most out of their investments by making upgrades to secure longevity and performance. However, while it’s important to address integral aspects like waterproofing and ventilation, few homeowners consider another important factor: the buildup of algae and mold on roof shingles.


While not a threat to your roof’s integrity, algae and mold buildup on shingles can be an unwelcome eyesore. Photo: Ross Roofing & Construction, Inc. (2014)

The good news is that unlike faulty waterproofing, which can result in expensive repairs or replacement, algae buildup on shingles won’t compromise a roof’s integrity. In most cases, buildup is manifested as black streaks or green patches, either in isolated areas or across the entire face of the roof.

There are a few factors that can increase a roof’s propensity to accumulate buildup. Algae and mold are most commonly seen on steep roofs with wood shake shingles—a natural product that provides an ideal surface for growth. Buildup is also more likely to occur on roofs in heavily shaded areas, whereas the UV exposure in sunny regions usually kills fungus before it can develop.

If your home is a prime candidate for algae buildup, there are a few preventative measures you can take. When replacing roof shingles, consider purchasing an algae-resistant product fortified with copper granules. If you’re not planning on replacing your shingles any time soon, an easy preventative step is to install a zinc or copper flashing strip near the roof’s ridgeline. When it rains, the rainwater will become infused with the copper’s algae-resistant properties, allowing it to kill fungal elements as it washes down the roof face.

While the installation of a copper strip can eventually clear up existing mold and algae, a quicker solution is to clean your roofing shingles. However, it’s important to exercise care, as incorrect methodology can do more harm than good. Avoid using overly harsh chemicals or tools (such as a power washer), which can cause damage. Instead, use a soft bristled brush to apply a weak solution of water and hydrogen peroxide before rinsing with a garden hose.

While you can clean shingles yourself, climbing on a roof is not advised for the inexperienced, as it’s a common cause of household injury. Instead, call a roof professional to handle the problem.

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