Champaign Roofing: Article About Identifying Black Roof Streaks
Black, unsightly streaks on roofs are a common sight in humid areas such as Illinois. Many people attribute them to mildew, dirt, defective shingles or stains, but in fact, they are caused by a type of blue green algae that spreads from roof to roof using airborne spores.
Many people have observed that they never used to see this kind of roof discoloration, and they are correct. This species has been slowly spreading from the East Coast westward over the last 30 or so years. The recent trend to install light colored "cool" roofs has also made the discoloration much more apparent on infected roofs.
Homeowners are often disturbed by the stains and wonder what they should do. Since this type of algae doesn't actually damage the roof or the shingles, homeowners don't really have to do anything to prevent algae stains. However, the discolorations can be very unsightly and can reduce the curb appeal and resale value of a house quite a bit.
One approach is to have a professional from Champaign Roofing wash the roof. Homeowners should resist the temptation to rent a power washer and blast away themselves because power washers can cause a lot of damage to asphalt shingles. A professional can swab the roof down with a special solution that will both remove the discolorations and inhibit further growth of the algae.
A roofing expert from Roofs By Rodger of Champaign IL would be happy to answer any question you have about roof replacement or siding.
This treatment will have to be repeated every 5 years or so.
An alternative is to install special algae resistant shingles. These shingles have copper granules incorporated into their structure. The copper inhibits the growth of algae. If a structure's shingles are fine and don't need to be replaced for some time, a roofer can come install special strips of copper or zinc coated metal along the ridges of the roof. These strips don't work quite as well as copper impregnated shingles, but they do release metal particles every time it rains that wash down over the roof and help inhibit the growth of the algae.
Homeowners tempted to simply live with the discolorations should check carefully to be sure they are actually caused by algae before opting to do nothing. Moss and fungi can and do damage shingles. Moss usually grows around the edges of shingles in a pattern that is easy to distinguish from the black spots and streaks of algae. Fungi tend to grow in only certain parts of the roof and are not usually black in color.