Have you ever noticed those black streaks that sometimes appear on shingle roofs? They aren’t discoloration from weathering; they’re algae, mold, mildew, lichen, or moss that grows in and under the shingles on parts of the roof that receive less sunlight, particularly in more humid areas of the country.
Dark roof stains caused by algae can absorb and trap heat under the roof, which can increase air conditioning costs, and shorten shingle life by causing shingles to lose their protective granules. Stains can also decrease the curb appeal of your roof. Obviously important for homeowners, this might be even more so for businesses that want to present an attractive façade to customers.
Cleaning your roof can help extend its lifespan if done properly, and it’s easy to do by yourself, as long as you take proper safety precautions beforehand. If you’re uncomfortable with working on your roof yourself, there are professionals that provide this service.
The best option for removing the black streaks is soft washing. Soft washing uses just a garden hose that applies very little water pressure, along with a solution to kill the organisms that cause the staining. You should never use a power washer on a shingle roof, as it will permanently damage the shingles.
Washing solutions vary. Cleaning products with bleach can be used, but that’s not always ideal because the runoff could affect siding, plants or trees, or other things near or under the roof. Commercial roof cleaners are also available. Soft washing may not show immediate results because, while the algae and moss are dead, it is not all washed out from the roof. Normal rain cycles should take care of the residual dark streaks over time.