Commercial rooftop solar can offer attractive project economics, but successful installation depends on more than available roof space. Roof condition, structural capacity, mounting design, logistics and installation quality can all determine whether a project performs as intended.
Jason McCabe, Technical Director for the UK and Ireland at Clenergy, argues that the assessment should begin with the building itself, particularly the condition of the roof and its supporting structure.
Assess the structure first
Most commercial buildings were not originally designed to accommodate hundreds or thousands of PV modules. Although roofs may have allowances for wind and snow loads, adding solar introduces further weight and loading considerations.
McCabe recommends assessing both structural capacity and condition. A calculation may indicate that the original roof design can support additional weight, but deterioration of the roof covering or substructure can change the situation.
For metal roofs, identifying the exact profile and selecting the correct fixing is also important, particularly with standing seam systems. McCabe believes a manufacturer site visit is often necessary to confirm suitability.
Avoiding installation shortcuts
Once construction begins, experience and workmanship become critical.
McCabe warns against substituting a specified mounting product for a cheaper alternative without confirming its suitability. Products that appear similar may be intended for different roof coverings or structural conditions, potentially undermining the original project design.
Key considerations include:
Roof and substructure condition
Structural loading
Correct roof profile identification
Appropriate fixings
Wind and snow loads
Manufacturer specifications
Commercial rooftop projects can introduce large numbers of modules and mounting points across a single building.
Managing ballast and concentrated loads
Flat roofs introduce another challenge. Ballasted systems often require greater weight around exposed edges and corners because of increased wind loads.
Those same areas can also experience greater snow accumulation. Combining high ballast with snow loads could therefore create excessive concentrated loading.
McCabe recommends considering suitable setbacks and avoiding high point loads. Distribution trays can help spread ballast weight across a wider area.
Attachment design varies according to roof construction, reinforcing the importance of matching the system to the individual building.
Design principles remain consistent
McCabe says the underlying design process should remain consistent whether the installation is a 4 kWp residential array, a 50 kWp flat roof system or a 500 kWp commercial pitched roof.
What changes significantly is logistics.
Smaller commercial systems may be supplied through distributors from existing stock, while an 800 kWp project could require direct deliveries from a UK warehouse, potentially divided across several days to suit site requirements and avoid disrupting distributor stock.
Onsite technical support can also help installers address questions about system layout and installation.
Local design and long-term value
McCabe sees country-specific mounting design as increasingly important. Construction practices differ between the UK, Ireland and other European markets, so products designed around local building methods can simplify installation and support compliance.
Warranty expectations are changing too. McCabe says 25-year warranties covering both products and design are now expected, rather than the 10 or 12-year terms previously considered sufficient.
Looking ahead, his main concern is installation quality. He would like to see closer regulation of structural assessments and installation standards, with less emphasis on selecting projects and components primarily on price.
For commercial rooftop solar, the lesson is simple: project quality starts before the first module is installed. Thorough roof assessment, appropriate mounting design and qualified installation can reduce the risk of structural and maintenance problems later in the asset’s life.
Read the full interview with Clenergy on commercial rooftop solar, structural assessment, mounting systems and installation standards in PES Solar: https://pes.eu.com/exclusive-articles/why-commercial-rooftop-solar-starts-with-the-roof