Roofing materials can prove the perfect breeding ground for lichen, a type of algae, and mold, given the right moist conditions. While lichen and mold tend not to cause any significant structural damage on their own, the organic matter can stain your roof even if you have darker asphalt shingles. Roof stains might not seem like a big deal if you have a three story house with a gabled roof that's only visible with a tall ladder. But if you have a showy mansard roof or a lower house, the roof stains can become highly noticeable from the street and throw off your home's curb appeal.
There are a few different ways you can try and combat the lichen and mold, remove the stains, and reduce the likelihood of the problem returning in the future. One method will require the assistance of a roofing contractor, but you should call in a roofing contractor for all of the steps if you don't' have the proper safety equipment to work on your roof.
Clean: Scrubbing with Water
If the lichen and/or mold are fairly fresh, the stains might be surface moisture rather than permanent stains. You can try cleaning up the area using a garden hose with an adjustable nozzle and a cleaning brush with stiff bristles and a long handle for ease of use.
Use a low to a medium pressure setting on the hose preferably with the water stream narrowed to focus only on the areas of mold and lichen. Try to avoid getting the water up under your shingles or blasting the asphalt with too high of water pressure. You don't want to damage your shingles trying to clean the roof.
Once the mold and/or lichen is wet, you can use the stiff brush to scrub at the crusted and darker areas to see if the problem is only a surface issue. If the darkness persists, you might have to do the job with a stronger cleaning solution.
Clean: TSP Solution
Trisodium phosphate, or TSP, is an effective outdoor cleaning solution that can do wonders for lichen and mold stains on a roof. But you do need to be careful using TSP as it is a hazardous chemical solution even while diluted. Make sure you wear proper safety gear including eye goggles and use a targeted application method rather than dumping the solution all over your roof.
You can mix one part of TSP cleaner, see the package instructions for exact measurement, with a half cup of warm water for a potent solution or up to two gallons of water for something a bit gentler. Dip the end of a stiff brush into the solution and apply directly to the stained areas. If the stains are larger, you can instead use a heavy duty sponge to dip into the bucket and apply the TSP solution. Make sure you are wearing gloves either way.
Allow the TSP to set according to package directions and then carefully rinse away with water. If the stains still persist, call a roofing repair company (such as Affordable Roofing & Gutters) for help and possible shingle replacements.
Prevent: Zinc Strips
Has lichen or mold become a consistent problem on your roof? Ask a roofing contractor to install zinc strips near the top of your roof. Falling rain water will wash zinc particles down across your roof. Zinc is a natural enemy of both mold and lichen. The zinc will erode any existing organic material and make our roof more protected against future invasions.