Architectural Considerations for Solar Panel Retrofitting on Low-Slope Roof Systems

In the United States and much of the world, the need for clean energy is increasing the appeal of adding solar panel systems to existing buildings.

Increasing Demand for Solar Panel Retrofitting

Throughout the world, existing building stock is being evaluated and inspected to determine the suitability of adding such systems to these roofs. Many of these retrofits rely on ballasted solar panel frames to hold the panels to the roof. In considering such an addition to your building, there are several important factors to consider before committing to such an installation.

Roof Structure Evaluation

First, the roof structure should be evaluated by a licensed design professional (structural engineer generally) to determine if the structural components of the roof (structural deck, primary structural members, secondary members, etc.) are able to accommodate the increase in load due to the solar panel array. This is especially important when a ballasted solar panel array is being considered, since the intent of a ballasted system is to rely on the weight of the ballast (usually concrete blocks) to hold the panels to the roof via gravity and friction. Such additional weight and their bearing areas must be considered to determine the structural suitability of such a retrofit. But, the structural evaluation is not the only factor to consider regarding the added weight of the system.

The individual roof components also need to be considered for suitability with the proposed solar panel installation. Roof components that may exist in any given roof assembly include insulation, cover boards, and the roof membrane itself. Roof cover boards (also referred to as protection boards) are commonly manufactured out of gypsum-based material and may not be able to withstand the additional compressive loads imparted by the solar panels and could lead to compression failure of the boards. This is also true of any insulation that may be installed over the roof deck. If insulation exists on the roof and does not feature a high compressive strength value, it is possible the new solar panels will sink into the soft insulation and cause ponding and puddling of the roof at the load points. As well, the roof membrane itself requires consideration, since the new solar panel frame will be bearing directly on the existing roof membrane. If the membrane is mechanically attached, fluttering and billowing of the membrane can occur during periods of high wind, and the potential exists to damage the membrane if such billowing of the membrane is excessive at the solar panel frame’s bearing points. A larger bearing area at the bearing points may be a suitable solution in such cases.

Fall Protection, Emergency Access, and Drainage Accommodations

Finally, the performance requirements of existing roofs need to be maintained when a solar panel system is to be installed. Some valuable considerations include the need for guard/fall protection at open roof edges. The building codes generally require such fall protection where roof equipment and appliances that require service are located within 10-feet of the roof edge. Since solar panels require routine cleaning and maintenance, it is a good idea to make sure the addition of the solar panels to the roof does not result in fall hazards by personnel tasked with cleaning and maintaining the panels.

As well, emergency personnel access (firefighters, etc.) is generally required to be maintained per the fire codes, and this access is generally required to be 4-feet wide, unblocked along the roof perimeter. Putting new solar panels within 4-feet of the roof edge may result in a roof that is not accessible for emergency personnel as required by the applicable codes.

Finally, drainage performance of the roof should be considered and maintained for any new solar panel system installation. For most low-slope roof systems, the applicable codes require a minimum of 1/4-inch per foot slope (2-percent) to accommodate drainage off of the roof. If the addition of a new solar panel system reduces the slope of the roof (structural deflection, compressed insulation and/or cover board, etc.), the result may be a roof that holds water and ponds rather than sheds water as required by code. Ponding and standing water on a roof surface can dramatically reduce the life of the roof system, resulting in premature deterioration and leaking of the roof.

In Conclusion

Therefore, when considering the addition of a new solar panel system to an existing roof, it is a good idea to make sure that such an installation does not negatively impact the existing roof. In addition to the above discussion points, all building codes must be complied with, all manufacturer and product instructions should be consulted and reviewed for compliance with solar panel incorporation, as well as industry standards (the National Roofing Contractors Association for example) should be consulted for other considerations. Ultimately, it is important to consult with a qualified and licensed design professional to ensure all applicable requirements are complied with so that the final result is a solar panel system that works effectively and does not negatively impact the roof upon which it was installed.