Mold

• Mold can grow on all types of roof shingles, including ones made of asphalt and wood. Mold spores are blown onto your roof by wind, where they lodge in crannies and crevices in shingles. Mold thrives in wet climates, especially in areas that experience many cloudy days. It can spread across your roof, but is usually concentrated in areas that are protected from wind or are often in shadow.
  
  

Issues

• Mold growing on roof shingles is unsightly; it can make your house look older or unkempt. When it rains, water that washes over the mold can become discolored. As the water spills down the side of your home, it can stain the paint or siding. While the stain can be cleaned, it will return after every rain shower. If you need to do any work on your roof, patches of mold can be dangerous slip hazards.
  
  

Solutions

• Wash your roof to get rid of mold. Mix bleach and water at a 1:50 ratio. Spray it on the moldy shingles and let it sit for 20 minutes. The bleach kills mold and removes any discoloration it has caused. After 20 minues, rinse the bleach solution away with your hose or a pressure washer. Avoid directing the water runoff toward plants on the ground; the bleach won't kill them, but it could cause temporary yellowing of leaves.
  
  

Considerations

• When working on your roof, always spray water and other liquids downhill from where you are standing. This reduces your risk of slipping and falling. While bleach kills mold growing on roof shingles, it won't prevent mold from coming back. If mold is a constant problem, install copper strips on your roof. Whenver it rains, ions from the copper strips are washed down your roof. The ions kill mold spores and form a protective barrier against future mold growth.