For many years, roof discoloration caused by algae has been observed throughout the United States and Canada. The discoloration usually has a brown to black appearance, and may be mistaken for fungus growth, soot, dirt, moss, or tree droppings.

Gloeocapsa magma is probably the most prevalent of several algae species that contribute to discoloration. All species are transported through the air, and tend to collect and grow upon roofing structures. Natural pigments produced by these algae may cause a white or light colored roof to gradually turn dark brown or black. Discoloration may appear as uniform discolorations or streaks. The algae discolorations should not be confused with moss or tree droppings, which typically produce only localized discolorations.

This type of roof discoloration has been most widespread in the Gulf States and along the Northwest and Eastern Seaboards. It is not, however, confined exclusively to these regions. Algae growth occurs to varying degrees in all regions of the country, especially those subjected to warm, humid conditions. It should be noted that almost all types of roofing systems are susceptible to algae discoloration. It is, of course, most readily visible upon light colored roofs, while it is not so visible upon darker shades of roofing.

Algae discolorations are difficult to remove from roofing surfaces, but may be lightened by applying a solution of liquid household chlorine bleach (sodium hypochlorite) and water. Directions for mixing solutions of these ingredients may vary among shingle manufacturers and depend on the amount of discoloration. A typical solution should be one part chlorine bleach and one part water. Other cleaning chemicals or methods should not be used without approval of the shingle manufacturer.

First, gently disperse this solution on the roofing surface. Use normal precautions for handling bleach including eye protection and rubber gloves. Be sure to apply it carefully to avoid damage to other parts of the building and the surrounding landscape. Avoid scrubbing the surface, as this friction may loosen and remove granules. If possible, always work from a ladder and/or walkboards to avoid direct contact with the roof surface. Observe all possible safety precautions when working on or near the roof. The solution should be left on the roof for at least 15 minutes but for no more than 20 minutes. Finally, rinse the solution from the roof by gently spraying the surface with water. Be warned that this solution application and rinse process will make the roof surface slippery and potentially hazardous to walk on during treatment.

The effectiveness of a cleaning technique is only temporary, and discoloration will likely reoccur. However, several types of algae resistant roofing products have been developed and are now commercially available. These asphalt roofing products are specifically designed to inhibit algae growth for extended periods of time.

Caution!

High pressure washing systems are likely to damage asphalt roofing and should not be used on asphalt roofing for removing algae or for any other purpose.

ARMA

Introduction
Photovoltaic (PV) systems convert sunlight into electricity. These systems have been successfully installed on residential asphalt shingle roofs for many years. The two common attachment methods are rack-mounted and roofintegrated: The latter method is sometimes referred to as building integrated photovoltaics. Framed rigid PV panels/modules are commonly mounted on racks attached to the roof’s supporting structure. PV panels with specialized frames may also be integrated into the shingle roof system. As with any roofing project, consideration of factors such as safety, design, codes, installation, and integration with other building components is necessary to obtain the desired results. Consult the PV system manufacturer, local building codes, and the asphalt shingle manufacturer for specific requirements. In the event that the specific roofing manufacturer is unknown, generally accepted roofing practices should be followed.

Safety and Proper Handling
If the proper precautions and protective equipment are used, PV systems can be installed safely and without incident. Several areas requiring attention are listed below.
• Fall Hazards: Working at heights can be dangerous. Follow all necessary precautions and safety guidelines in accordance with OSHA regulations and proper roofing practices, including the use of appropriate fall protection/fall arrest equipment.
• Shock/Electrocution Hazard: PV modules generate an electric current. Do not drive nails or screws into any part of the PV module other than in locations specified by the manufacturer. Follow the PV manufacturer’s
mounting instructions and local code requirements (building code and fire code) for location of panels and wiring. Avoid contacting free ends of connectors with metallic objects and do not install in wet conditions.
• Additional Safety Precautions: Additional safety information can be found in the National Roofing
Contractors Association’s “Guidelines for Roof-mounted Photovoltaic System Installations” and in NEC Article 690.

Design, Installation, and Maintenance
• Local codes increasingly contain specific requirements for PV system installation. These requirements should be followed carefully to ensure the safety of the home’s occupants, firefighters, and anyone that may be performing work on the roof or in the attic of the home.
• All vertical and horizontal loads from the PV system should be transferred to the building structure without deformation or overloading the roof system or its components.
• Ensure that the arrangement and location of the PV system installation on or above the roof deck do not interfere with the effectiveness of other roof system components. Provide sufficient clearances around the PV system for roof venting (per local fire code) and regular maintenance.

• In colder climates, drifting snow or ice dams in/around rack-mounted PV systems may increase roof loads beyond the original design criteria, may cause a blockage of other roof components, and may create the potential for large areas of snow to slide off the PV system surface. Installation of snow guards on the roof may be advisable.
• Typically, PV systems should be installed concurrently or shortly after the installation of new asphalt
shingles. Doing so will reduce the chance of roof deterioration before the service life of the PV system is reached.
• Proper waterproofing and flashing of mounting locations where PV system components intersect with or penetrate the shingle layer is critical and must be done carefully to ensure the roof system’s long-term water-tightness.
• Consider a semi-annual roof/PV system inspection and maintenance program performed by a professional roofing contractor, per National Roofing Contractor Association recommendations.

Important Legal Disclosure
This Technical Bulletin is not intended to provide a comprehensive list of all safety precautions, design considerations, installation practices, or maintenance requirements relating to PV systems on asphalt shingle roofs. Rather, it provides an overview of some important issues one should consider when contemplating PV system installation. Asphalt shingle roofs can provide a suitable substrate for commercially available PV systems; however, it is important that the roof system and the PV system be constructed and installed in compliance with all requirements of applicable building code(s), the shingle manufacturer, and the PV system manufacturer. ARMA makes no warranties or representations regarding the suitability of PV systems for, or the performance of PV
systems installed on, asphalt shingle roofs.

NRCA Roof-Mounted Photovoltaic System Installations Guide
For additional information on photovoltaic systems on asphalt shingle roofs, see the National Roofing Contractors Association’s Guidelines for Roof-Mounted Photovoltaic System Installations.

Technical Bulletin ARMA Report (PDF)