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)

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.

To find a Diamond Certified roofing company in your area, click on one of the links below.

Alameda County: www.diamondcertified.org/alameda-roofing, www.diamondcertified.org/alameda-roofing-commercial
Contra Costa County: www.diamondcertified.org/contra-costa-roofing, www.diamondcertified.org/contra-costa-roofing-metal
Marin County: www.diamondcertified.org/marin-roofing
Monterey & San Benito Counties: www.diamondcertified.org/monterey-san-benito-roofing
Napa County: www.diamondcertified.org/napa-roofing
San Francisco: www.diamondcertified.org/san-francisco-roofing
San Mateo County: www.diamondcertified.org/san-mateo-roofing
Santa Clara County: www.diamondcertified.org/santa-clara-roofing, www.diamondcertified.org/santa-clara-roofing-commercial, www.diamondcertified.org/santa-clara-roofing-metal
Santa Cruz County: www.diamondcertified.org/santa-cruz-roofing
Solano County: www.diamondcertified.org/solano-roofing
Sonoma County: www.diamondcertified.org/sonoma-roofing

Read more:
Making the Most of a Roof Replacement

Tips for Maintaining Your Roof


5 Responses

  1. Caleb Hart says:

    I had no idea that algae could build on the top of a roof. My parents have been thinking about getting their roof cleaned. I wonder if it’s because they have algae on their roof. Maybe I should check my roof and see what is on it.

  2. DoloresB says:

    It’s good to have a roofing contractor check out your roof periodically. That way they can catch any problems early and repair them so they don’t become bigger. You can save a lot of money and frustration that way.

  3. Delores Lyon says:

    Thanks for sharing this advice on preventing algae buildup on your roof. I think it is really nice that this mold doesn’t actually weaken the roof, even though it is very unsightly. There is actually a bit of algae on the roof of my house, and I was worried that it might be damaging it. However, I’ll still probably try getting algae-resistant shingles with copper granules to make sure that it doesn’t come back.

  4. I’m glad that you posted about this issue. It wasn’t until recently when I noticed that my roof started building up some algae. This is really unusual to me, because I’ve never had a problem with algae buildup in my roof. After reading the section about what contributes to algae buildup, now I can see why I’m starting to see algae growing on my shingles. I installed a new roof using wood shake shingles, so now it makes sense to me why it’s been growing algae.

  5. Eliza Cranston says:

    Thank you for the tips on getting rid of roof algae! I live in a really rainy area and I’ve noticed green streaks on my roof. I’ll try out the water and hydrogen peroxide suggestion.

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