Mold accrues on shingle roofs frequently. Roofing is susceptible to mold and mildew when it does not receive enough sunlight or wind movement to properly dry the shingles leaving them with excess moisture and normal bacteria’s which cause green algae and mold to build up on the shingles. A common question from homeowners is how to get rid of the unsightliness without doing damage to the roofing or shingles.
The mold that can be seen some times is green mossy or black mold can appear in blotches or streaks on the roof. This is especially true of light colored asphalt shingles. The blue-green mossy algae are usually found in warm climates or humid summers. Although it is unsightly it does not usually do damage to the roofing material itself.
As for getting rid of the algae there are several ways to go about it. The first is to completely remove and replace the shingle roofing material with dark shingles. This will remove the issue currently and hopefully help you disguise the staining and moss growth later on down the road. Replace the roofing material with shingles that have copper granules and this will prevent the algae from forming as the copper is lethal to algae. A complete roof replacement is only needed if the current roofing material is in need of being replaced. This is the least cost effective manner in which to rid your roof of algae and moss.
Another technique that can be used to remove the algae on the shingle roof and is least expensive is to spray the roof down with a mixture of bleach and water. A 50/50 mix is best and will leave the roof clean without removing the granules on the shingles or bleaching the color out. No matter what do not use a power washer. This will remove the granules on the. shingle which will lead to the deteriorating of the material. Also it is important if you have landscaping below make sure you saturate the landscape with clean water before and after the job. Plants are notorious for not thriving in an environment when covered in bleach water.
To keep the algae from coming back add a piece of six inch strip of copper under the shingles at the roofs peak. The metal molecules will wash down with the water and will prevent algae from being able to foot into the shingles in the future. This is the same true of the copper flashing around the chimney. Look around at the roofs around you. Any of them with copper flashing are probably free of algae.
As always I do believe it is best to have a professional come and evaluate the situation. I think this is the best practice to ensure that there are not other issues that are causing the mold issue on the shingles. They also can remove the mold and algae and prevent damage to the shingles. As homeowners we tend to over clean the shingles which damages the structural components of the shingling.