In the first part of this two-part article, I explored the types of roof membranes and roofing systems commonly found in commercial and industrial (C&I) buildings. Identifying the type of roof is a crucial first step when planning for roof-mounted solar installations. This information directly influences other design and engineering decisions, such as structural support, waterproofing, and balance of system (BOS) requirements. While these factors come after initial roof identification, they are just as vital—ensuring that the solar system remains secure, doesn’t compromise the integrity of the building, and doesn’t lead to leaks or structural failures.
Structural Considerations
The most critical aspect of any C&I roof-mounted solar project is the structural assessment and engineering. A thorough evaluation ensures that the building can safely support the additional loads from the solar array. Here’s a closer look at some key considerations:
Reserve Capacity Evaluation. Most C&I buildings are designed to meet minimum code requirements, not necessarily to handle extra loads. Adding a solar system can increase both gravity and lateral loads, which must be carefully assessed. A qualified structural engineer should review the building's original plans or conduct an on-site inspection to determine if the structure has enough reserve capacity. They’ll also consider any modifications made over time, like new rooftop equipment or added roofing layers, which could affect load distribution.
If the existing structure isn't up to the task, reinforcement may be necessary. The engineer must choose the most cost-effective and practical solution, ensuring long-term safety and performance.
Mechanical Attachments. While ballasted systems are common for low-slope roofs, some projects or local regulations require mechanical attachments. These can help reduce dead loads by distributing weight more efficiently. Mechanical attachment details must align with the specific roof construction. For example, thick insulation layers might need to be replaced with wood blocking to prevent torsional deflection.
Different attachment methods, like U-bolts, OMG Power Grips, or S-5! clamps, are used depending on the roofing system. When working with standing seam metal roofs, it's essential to identify and assess the existing connections between panels and the structure—often a hidden but critical detail.
Roof Loading Plan. Once installed, solar systems distribute weight evenly across the roof. But during installation, materials like modules, inverters, and ballast are concentrated in certain areas. A proper roof loading plan ensures that heavy items are placed over strong structural elements, like beams or columns. It also specifies how much weight each area can hold, helping to avoid damage during the installation phase.
Waterproofing Considerations
Even with strong structural support, a roof-mounted solar system must not compromise the building’s waterproofing. Every penetration into the roof presents a potential leak point, so careful planning is essential.
Courtesy OMG Roofing Products
Roof Flashing and Drainage. Proper flashing is essential to prevent water infiltration around penetrations. It involves using compatible materials to seal joints, seams, and intersections. Coordination between the solar contractor and a professional roofer is key to maintaining the integrity of the roof system and preserving any existing warranties.
Low-slope roofs aren’t flat—they’re designed with slight slopes to allow water to drain. Solar installations must not interfere with drains, scuppers, or crickets. If water pools on the roof, it can cause structural stress and accelerate roof degradation, potentially leading to PV system failures.
Preventing Roof Damage. Single-ply membranes are vulnerable to physical damage during and after installation. Foot traffic, dropped tools, and environmental forces like wind and temperature changes can all contribute to wear. Installers can use temporary walkways, protective pads, or slip sheets to minimize contact between the mounting system and the membrane.
Additional walkways may be needed permanently to accommodate ongoing maintenance and access. Planning for these early helps protect the roof and extend the life of the entire system.
If you're looking for more tips to de-risk your C&I roof-mounted PV project while maximizing performance, contact Pure Power Engineering to learn about our value-engineered design and construction drawing services. We specialize in helping clients achieve safe, efficient, and long-lasting solar solutions.
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