- Mold can grow on roof shingles if they have ample amounts of water and dirt. The dirt provides nutrients for the mold, and the moisture allows mold spores to germinate. Mold will grow most often after periods of extended rain, when moisture fails to evaporate quickly, or during seasons of high humidity, when water vapor clings to the roof shingles. Cracks and holes in the roof shingles can also cause moisture to become trapped, which can further contribute to mold growth.
- Mold is not the only organism that grows on roof shingles, so it first helps to identify exactly what problem you have. For example, if the growth appears thick and grassy, it likely points not to mold but to moss, another problem related to excess moisture. If the growth looks thick, slimy and green, you probably have algae. Mold will typically appear in thin, velvety patches, penetrating the surface of the shingles and emitting a musty odor. Mold can appear black, brown, white, gray and in some cases dark green.
- You can kill mold -- as well as moss and algae -- on your roof using household bleach. Mix it with equal parts water, spray it over your mold and start scrubbing with a scrub brush. Then rinse away the remains with your garden hose or with a second spray bottle. Start by watering any nearby plants or grass, as the water will help protect them from the effects of bleach runoff.
- Mold cannot grow unless it can feed on nutrients, and roof shingles contain no natural nutrients for mold spores. As long as you keep your roof shingles clean and free from excess dirt, mold has no way of growing, even if plenty of moisture exists. Even hosing down your roof each week can go a long way in preventing the growth of mold and algae.
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