How solar panel weight may TRIGGER structural code compliance for commercial rooftops.
Commercial solar rooftops O-PLENTY; can yours handle the weight?

How solar panel weight may TRIGGER structural code compliance for commercial rooftops.

These days, utility companies and solar integrators have been looking forward to the vast amount of commercial rooftop space awaiting solar deployment.  But while owners of this un-pioneered space are keen to see solar implementation, this “run on rooftops” doesn’t come without its own unique set of obstacles.

Many Rooftops Are Not Solar-Ready

In some U.S. markets, over 75% of commercial properties are structurally unsuitable, as rooftops are not engineered to support the weight of large solar arrays. This is especially true in Southern California, which holds the largest market in the U.S., but where only 20% of rooftops are sturdy enough to carry significant solar panel structural loads.
No surprise here, since statistically most roofs were designed primarily to protect the building, and not to support additional dead-weight or scattered equipment loads.  

Stricter Building Codes… Cost Prohibitive

With today’s building codes becoming ever stringent, developers and property owners are having to dedicate excess funds just to keep current with code changes, leaving little cash for voluntary upgrades in which to support the weight of a future solar investment.  In fact, depending on equipment selection, a fully installed photo voltaic system may typically weigh between one to eight pounds per square foot.  A rooftop supporting an energy system covering an area of 200,000 square feet, at five pounds per square foot could amount to a staggering one million pounds!

Additional hindrances?  Structural codes in California are becoming more vigilant with the need to allow for anticipated seismic activity; this includes the California 1997 Uniform Building Code (UBC), which calls for stepped-up design standards for buildings located near a fault.  Also, the International Building Code (IBC) of 2006 and the California Building Code (CBC) of 2007, both of
which incorporate the survey of soil conditions in areas of seismic activity.  The result of these code changes is that the majority of buildings completed before 1997 are not strong enough for a utility-sized solar installation.

No Excess Structural Capacity Available

At the present time, most of the available commercial properties don’t have excess load bearing capacities built into them.  In order to be considered as suitable candidates for solar installations, these properties would have to undergo costly structural upgrades due to the prevailing conditions that these systems present.   For instance, racking systems that attach directly to the roof can cause the purlins to be overloaded, and, when seismic conditions are factored in, a solar energy system can result in the buildings structural stress levels breaching unsafe levels.  Further adding to this dilemma is simply bringing a building “up to code”, which may end up causing other codes to be triggered, resulting in even more costly upgrades.

The Newer, the Better – Or Is It?

Most commercial buildings constructed prior to 1997 will not pass unscathed; in total, nearly 80% of industrial properties may require extensive retrofits.  To add to the conundrum, a building may not be judged by its relative youth alone.  For example, two sites were considered for solar installations; one was built in 2005 with a square footage of 645,000, but found unacceptable due to structural issues.  The other site was also built in 2005, with a square footage of 435,000, but in this case the roof was designed with excess capacity, allowing for the addition of solar equipment at 5 pounds per square foot. The point here is that even buildings that are relatively new may not meet the required standards, and so each building, regardless of age, needs to be evaluated on its own merits.

What Does The Future Hold?

The intention is to have 636 megawatts of solar installed on commercial property by 2016, covering approximately 159 million square feet of roof space, or around 15.5% of all the currently available commercial roof space. That is a full 250% more than the amount of roof space available meeting current code standards.  In response, the solar industry is working hard to develop lighter technology to meet the needs for rooftop solar.  Solar laminates weigh in at only one pound per square foot and attach directly to the roof, and traditional PV systems are gradually getting lighter, with thin film technology at the forefront of lighter, cheaper technology.

But if older buildings are to be used, the technology needs to be made still lighter to escape the need for prohibitively expensive upgrades.  Financial assistance and incentives would make upgrades to older buildings more feasible and encourage developers to build new commercial property, not only sturdy enough to support large-scale solar installations, but to build in excess capacity to allow for future solar expansion.


Article by Jennifer Coleman of Sun Source Solar Brokers, a solar brokerage and energy consulting business serving Sonoma Marin and Napa counties, including the San Francisco Bay Area.


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