Can You Prevent Algae Growth on Roofs?
Algae often appears on shingle roofs as long black or blue-green streaks. Learn more about how to fix and prevent algae growth.
Algae often appears on shingle roofs as long black or blue-green streaks. Learn more about how to fix and prevent algae growth.
Roof algae appears in various forms. Most commonly, it grows in long, vertical black or blue-green streaks that run down the shingles, usually starting near the roof ridge and washing downward with the rain.
Algae is not the same as moss, lichen, or mold, and noticing growth shouldn’t be an immediate cause of concern because it’s mostly an aesthetic issue.
The good news is that it can be treated after you notice growth, and even better, it’s fairly easy to prevent.
Algae growth is most common in damp or shaded areas of the roof. Algae also commonly appears in parts of the roof that are slow to dry following rainfall. Once airborne spores (carried by wind, rain, or birds) land on your roof, they attach themselves and grow, feeding on the limestone filler that’s used in most asphalt shingles, and as they grow, develop a pigmented sheath for protection.
Algae needs moisture to multiply, so it’s important that you’re not inadvertently feeding their growth due to drainage issues. Ensure that your gutters are clear and that any rainfall is draining properly from your roof. Get into a habit of cleaning out your gutters at least twice a year, ideally once in the spring and again in the fall. If you live in areas with dense foliage, we recommend cleaning them more frequently or investing in gutter guards to prevent debris accumulation.
The best way to see if you have drainage issues is to walk the perimeter of your home during the next rainstorm. If rain is running over the gutters and downspouts aren’t discharging water properly, check for obstructions.
Tree branches can shade parts of your roof. Trimming tree branches helps prevent potential impact damage during inclement weather while allowing your roof to get more sun and dry out algae spores.
The best solution to prevent algae growth is investing in the right roofing system, especially if you’re in a naturally shaded area that even tree trimming can’t fix. L&S Home Improvements is a strong proponent of CertainTeed’s Integrity System, which features asphalt shingles with copper-containing granules that provide reliable, long-term protection against algae growth.
Algae growth won’t immediately impact the structural integrity of your roof. However, it can degrade the shingles over time. Some of the long-term risks of untreated algae growth include:
The Internet is rife with bad DIY Reddit suggestions. If you want to remove growth without damaging your roof, DO NOT use bleach or a pressure washer. Bleach will stain your roof and, if allowed to run over the roofline, can stain your siding and kill your plants. Pressure washers will blast the granules right off your shingles, leaving your roof compromised to UV damage.
The best removal method is soft washing with a roof-safe cleaner. We recommend hiring a professional cleaner, especially if your roof is steep and you don’t feel safe accessing it.
We have a saying at L&S Home Improvements: if something seems or feels wrong, it probably is wrong.
If you’ve noticed discoloration on your shingles (or any other type of shingle damage), contact L&S Home Improvements today for a free roof inspection, especially if you’re not sure how long the damage has been there. Our experts will inspect not just the roof, but also the attic to ensure any moisture issues and other harder-to-find roofing problems are identified sooner rather than later. Our team can help with any needed shingle repairs or roof system replacements to ensure you stay protected.
