In the first part of this two-part article, I discussed the common types of roof membranes and roofing systems used in commercial and industrial (C&I) buildings. Accurate roof identification is crucial because it directly influences other design and engineering decisions for roof-mounted solar installations. While these follow-up considerations may not be the primary focus, they are essential to ensuring the long-term success and safety of the project. After all, proper structural, waterproofing, and balance-of-system (BOS) planning ensures that the solar system remains secure and doesn’t cause damage or leaks.
Structural Considerations
When it comes to C&I roof-mounted solar projects, the structural assessment is often the most critical step. A thorough evaluation helps determine if the existing building can safely support the added weight and stresses from the solar array. Here’s a closer look at some key factors involved in this process.
Reserve Capacity Evaluation. Most C&I buildings are designed to meet minimum load requirements set by local codes. Adding a solar system could exceed those limits, which poses serious risks. A qualified structural engineer should review the building’s original plans or conduct an on-site inspection to assess whether the structure has enough reserve capacity to handle the additional loads. This includes evaluating both gravity and lateral forces from the solar equipment, as well as any changes made to the building over time, such as new rooftop units or extra layers of roofing.
Mechanical Attachments. While ballast is commonly used for low-slope roofs, some jurisdictions require mechanical fastening. In such cases, attaching the system directly to the roof structure can help reduce dead loads, especially when the building’s load capacity is limited. The engineer will specify the number, location, and type of attachments needed. For example, U-bolts, OMG Power Grips, or S-5! clamps may be used depending on the roof type. On standing seam metal roofs, identifying and assessing the existing attachment points is especially important, as they can be difficult to access and inspect.
Roof Loading Plan. During installation, the weight of PV modules, inverters, mounting systems, and ballast is concentrated in specific areas. A detailed roof loading plan ensures that materials are staged strategically over strong structural elements like beams and columns. It also outlines safe weight limits for each staging area, helping prevent overloading and potential structural issues during the installation phase.
Waterproofing Considerations
Even with strong structural support, roof-mounted solar systems must be installed in a way that maintains the integrity of the roof membrane and drainage system. Any penetration or disruption can create a pathway for water to enter, leading to costly damage and leaks.
Courtesy OMG Roofing Products
Roof Flashing and Drainage. Proper flashing is essential to prevent water infiltration around penetrations and joints. Coordination between the solar contractor and a professional roofer is key to ensuring compatibility and proper installation. Additionally, it’s important to preserve the existing roof’s drainage features—such as slopes, crickets, and scuppers—to avoid water ponding, which can lead to premature roof failure and even PV system issues.
Preventing Roof Damage. Single-ply membranes are vulnerable to damage during and after installation. Foot traffic, dropped tools, and environmental stressors like wind and temperature fluctuations can all harm the roof. To mitigate this, temporary protection like walkways and cushioned zones can be used during installation. Permanent solutions, such as slip sheets or separator pads, act as a protective barrier between the mounting system and the roof membrane. In some cases, additional permanent walkways may be necessary to accommodate ongoing maintenance and access.
If you're looking to minimize risks and maximize performance in your C&I roof-mounted solar project, contact Pure Power Engineering to learn more about our value-engineered design and construction drawing services. We’re here to help ensure your solar installation is both safe and efficient.
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