In the first part of this two-part article, I discussed the various types of roof membranes and roofing systems commonly used in commercial and industrial (C&I) buildings. Identifying the roof type is a critical first step in planning for a roof-mounted solar installation, as it influences many subsequent design and engineering decisions. While these follow-up considerations may not be the primary focus, they are essential to ensuring the long-term performance and safety of the system. After all, proper structural support, waterproofing, and balance of system (BOS) planning prevent potential issues such as roof collapse, water leaks, or even solar panels being blown away.
Structural Considerations
When it comes to C&I roof-mounted solar projects, the structural assessment is arguably the most crucial phase. A thorough evaluation ensures that the building can safely support the added weight and environmental stresses of the solar array. Here are some key areas to consider during the structural analysis.
Reserve Capacity Evaluation. The structural components of existing C&I buildings are typically designed to meet minimum code requirements. Adding a solar array can push those limits, so it's essential to have a qualified structural engineer assess whether the building has enough reserve capacity to handle the additional loads. This process involves reviewing as-built drawings or conducting a site inspection to understand the current conditions and how they differ from the original design. Any changes made over time—such as new rooftop equipment or extra layers of roofing—must also be considered.
Mechanical Attachments. While ballast is a common method for securing solar arrays on low-slope roofs, some projects or local regulations require mechanical fastening. These attachments must be carefully planned to avoid unnecessary stress on the roof structure. For example, in some cases, insulation layers may need to be removed and replaced with wood blocking to reduce torsional deflection. Different attachment methods, like U-bolts, OMG Power Grips, or S-5! clamps, are used depending on the roofing system. When using S-5! clamps on standing seam metal roofs, it's important to identify and inspect the existing connections between the roof panels and the structure.
Roof Loading Plan. Once installed, the solar system distributes its weight evenly across the roof. However, during the installation phase, the concentrated load from PV modules, inverters, and ballast can place significant stress on specific areas. A detailed roof loading plan helps ensure that materials are staged over structural elements like beams or columns, which can temporarily support heavy loads without risking damage.
Waterproofing Considerations
While structural integrity is vital, waterproofing should never be overlooked. Each penetration created for mounting hardware represents a potential entry point for water. Proper flashing, drainage, and protection are essential to maintain the roof’s integrity and extend its lifespan.
Courtesy OMG Roofing Products
Roof Flashing and Drainage. Effective flashing is crucial to prevent water infiltration at roof penetrations, joints, and transitions. It requires close coordination between the solar installer and a qualified roofing contractor to ensure compatibility and proper installation. This collaboration also helps preserve any existing roof warranties. Low-slope roofs, often mistakenly called "flat," rely on features like slopes, crickets, and scuppers to manage water runoff. Solar installations must not interfere with these systems, as blocked drainage can lead to water ponding, increased load, and premature roof failure.
Preventing Roof Damage. Single-ply membranes are vulnerable to damage during and after installation. Tools dropped during setup, repeated foot traffic, or long-term exposure to wind and temperature fluctuations can all cause wear. To mitigate this, temporary protective measures like walkway reinforcements or cushioned zones can be used during installation. Permanent solutions, such as slip sheets or separator pads, act as a barrier between the mounting system and the roof membrane. In some cases, new walkways may need to be permanently installed to accommodate ongoing maintenance access.
If you're looking for practical advice on reducing risks and maximizing performance in C&I roof-mounted solar projects, contact Pure Power Engineering to learn more about our value-engineered design and construction drawing services.
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