As mentioned in the previous post, it is common for homeowners to experience dark stains or streaking on their shingles as a result of algae growth. These stains tend to be more of an eye sore than anything so if removing them is on your spring cleaning list, it’s important that you go about the process safely. Before you bust out the power washer, keep in mind that the cleaning technique you use is dependent on the type of shingle installed on your roof.
For example, asphalt shingles are more disposed to algae growth due to a component, calcium carbonate, used to manufacture the shingle which algae love to feed on. Calcium carbonate is pulverized limestone working as a filler in the shingle while also helping to enhance the actual performance of the shingle over it’s lifetime. Calcium carbonate aids in mitigating moisture and slows down the aging and oxidation process. The texturized granules also work as a UV barrier from the sun’s harmful rays. Blasting away any of these essential calcium carbonate granules can quickly compromise the protective properties of your asphalt shingle.
Instead, consider a topical cleaning solution that can be gently sprayed on the surface of your roof. There are a variety of options: chlorine bleach solution, oxygenated bleach, sodium hydroxide (degreaser), trisodium phosphate, and so on. Some of these solutions can be mixed at home or there are plenty of manufacturers who sell bottled roof cleaning products.
Another option that does not involve chemicals? Consider a installing a copper or zinc strip along the ridge line of your roof. As rainwater passes down from the ridge into your gutters, the metal elements contained in the copper or zinc provide a “poisonous” bath to algae living on shingles. If you have stains from algae, you may notices growth patterns trend away from any areas of your roof with metal flashing installed around vents, chimneys, etc. Installing an entire ridge line strip of copper or zinc, with 2-4 inch exposure, has been observed to be effective defense against algae growth across a large variety of shingles and tiles. One possible drawback: experts worry traces of these metals in water runoff can be toxic to aquatic life.
Regardless of the route you choose, be sure to do your research on possible effects of your chosen method on the environment as well as how these solutions can affect your gutters, siding, landscaping, and ground water after run off.