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In this two-part series, the first segment focused on the various roof membranes and roofing systems typically found in commercial and industrial (C&I) structures. Understanding these elements is crucial since they form the foundation for subsequent design and engineering decisions when integrating solar panels on rooftops. Although secondary to roof identification, these follow-up considerations remain vital to ensuring that rooftop photovoltaic systems are safe, stable, and won’t compromise the integrity of the roof.
### Structural Considerations
Arguably, the most pivotal aspect of a C&I rooftop solar project lies in its structural evaluation and engineering. Below is a concise overview of key areas that need to be addressed during this phase:
#### Reserve Capacity Assessment
The structural components of existing C&I buildings are generally designed to meet the minimum load requirements set by relevant codes. Exceeding this structural capacity can lead to disastrous outcomes. Thus, it’s essential to have a structural engineer assess the current structure's envelope to determine if there’s enough reserve capacity to support a new solar array.
To accomplish this, the engineer will either review the as-built blueprints, if available, or conduct a site inspection to evaluate the actual condition. The structural analysis must account for the extra gravitational and lateral loads introduced by the new solar equipment and compare them against the existing building's capacity. Additionally, any modifications made to the building throughout its lifetime, such as adding rooftop units or extra roofing layers, should be taken into consideration.
In some instances, the existing structure might already have the necessary reserve capacity for the solar installation. In others, targeted structural reinforcements may be required. Consequently, the structural engineer should possess extensive expertise in this area to propose the most efficient and cost-effective solutions.
#### Mechanical Attachments
Although many low-slope C&I rooftop solar projects depend on ballasting to counteract wind uplift, certain projects or regions mandate mechanical attachments. For instance, in a ballasted setup, connecting the solar equipment directly to the roof structure can help reduce dead loads, especially when faced with limited load-bearing capacity constraints.
A detailed structural plan not only specifies the number and placement of these attachments but also outlines the necessary hardware specifications. Ideally, the mechanical attachment details should factor in the specific characteristics of the roof construction. Some roofing systems feature a thick layer of insulation between the roof deck and the membrane. Removing and replacing this insulation with wooden blocking can minimize torsional deflections.
Different mechanical attachment techniques cater to varying roofing systems. Common hardware includes U-bolts, OMG Power Grips (as shown below), and S-5! clamps. When employing S-5! clamps on standing-seam metal roofs, it’s crucial to pay attention to the hardware securing the roof panels to the underlying structure, which isn't always easy to identify.
#### Roof Loading Plan
After installation, the weight of a rooftop solar system is evenly distributed across the roof. However, during the staging phase, the concentrated dead loads of PV modules, inverters, mounting systems, and ballasts pose significant risks.
A roof loading plan ensures that pallets of construction materials are positioned over structural supports like columns, beams, or walls that can temporarily bear these concentrated loads. Besides identifying optimal staging spots, the plan also offers guidance on how many pallets or the total weight each location can handle.
### Waterproofing Considerations
While structural attachments safeguard against wind uplift and other external forces, every penetration through the roof presents a potential entry point for moisture. Furthermore, solar installations must be planned in ways that avoid damaging the roof membrane or obstructing drainage.
*Courtesy: OMG Roofing Products*
#### Roof Flashing and Drainage
Flashing involves using compatible, waterproof materials to seal off roof penetrations and prevent water infiltration at joints and intersections. Effective flashing requires collaboration between the solar EPC and a qualified roofing expert. Engaging a roofer ensures compatibility of materials and proper installation, which could preserve the existing roof warranty.
Despite common misconceptions, low-slope roofs aren’t truly flat—they rely on shallow inclines, crickets, drains, and scuppers to direct water away from the building. Retrofitting solar systems should not interfere with these drainage mechanisms. Pooled water not only adds unnecessary weight but also accelerates roof deterioration and can cause certain PV systems to fail in the field.
#### Preventing Roof Damage
Single-ply membranes are vulnerable to physical harm during and post-installation. Foot traffic and dropped tools during construction, along with long-term exposure to environmental factors like wind forces and thermal expansion, can all contribute to membrane damage.
Installers can mitigate these risks during installation by using temporary protective measures for walkways and loading zones. Permanent solutions often involve using roof-friendly slip sheets or separator pads to serve as sacrificial barriers between the mounting system and the membrane. It’s worth noting that additional permanent walkways may be needed to accommodate increased foot traffic over the life of the PV system.
For further insights into minimizing risks and enhancing performance in C&I rooftop PV projects, contact Pure Power Engineering to explore their value-engineered design and construction drawing services.