You used to appreciate the appearance of your roof, since you carefully chose the color and pattern of the asphalt shingles to enhance your home's beauty. Now, however, the roof has developed dark streaks that you can easily see as you ride by the house or pull into the driveway. What's causing this problem—and what can you do to resolve it? Fortunately, you can remove those streaks yourself with a little elbow grease, or have a roofing contractor do the job for you.
Dark streaks on roofs can be caused by dirt or mildew, but typically those streaks come from algae. These algae like humidity and shade from trees. They don't like copper or zinc, so they don't tend to grow under flashing or galvanized vents.
How to Fix the Problem
At a hardware store or home improvement store, you can buy commercial products specifically designed to remove algae from roofs. You also can use a quart of bleach with a gallon of water and 1/4 cup trisodium phosphate.
Apply the solution with a spray device—but not a pressure washer, as that can damage shingles. If the problem is a stubborn one, you may need to scrub the area with a soft brush. You can do this while standing on the roof or by using a brush attached to a telescopic pole. After 20 minutes, rinse the liquid off with your garden hose.
Do the project on a cloudy day or when the area has shade. That way, the solution doesn't dry up before you hose it off.
Protect the grass and other plants under your work area by hosing them down before and after you do the job. You also might cover them with a tarp or sheets of plastic before you start work.
Installation of a strip of galvanized sheet metal or copper under the ridge will stop the problem from happening again. When it rains or when snow melts, ions washing down from the metal kill the algae. A roofing contractor can do this project at an affordable price.
It's possible to resolve this problem yourself. However, you may not feel comfortable doing all that work far above the ground, whether you stand on a ladder or get up on the roof itself. If that's the case, contact a few local roofers, such as Lask Roofing and Siding Inc., and ask what they charge for this type of project. Soon your roof will look great again, and you'll be pleased with the results.