Before you put solar on a factory roof: structural checks

Rooftop solar is often the fastest route to lower power costs for a factory or warehouse — no land to acquire, no long transmission line. But the roof becomes a structural and operational dependency for the life of the system. A few checks before design starts prevent expensive problems later.

1. Load capacity

A solar system adds dead load (modules, mounting structures, cables) and affects wind load on the roof. Maintenance access adds live load. A structural engineer should confirm:

• The roof structure's design load and current utilisation
• Whether purlins, trusses and connections can carry the added load
• Wind uplift and how the mounting system transfers loads to the structure

If the structure is marginal, the options are strengthening, a lighter mounting design, or using only the strongest roof sections.

2. Roof type

3. Roof condition and remaining life

A solar system is a long-term asset. If the roof will need replacing within a few years, removing and reinstalling the system later adds cost and lost generation. It is usually better to repair or replace the roof first. Look for corrosion, leaks, damaged sheets and weak fixings.

4. Waterproofing

Every penetration through the roof is a potential leak. Good practice:

• Prefer non-penetrating mounting where structurally possible
• Where penetrations are needed, use detailing approved for the roof type
• Agree responsibility for leaks in the EPC contract
• Inspect waterproofing after installation and after the first monsoon

5. Orientation and shading

Roof orientation and pitch affect yield. Check for shading from parapets, water tanks, chimneys, ventilators and neighbouring buildings. Equipment that will be added to the roof later (HVAC, exhausts) should be accounted for in the layout.

6. Access, walkways and safety

Maintenance staff need safe access for cleaning and inspection. Plan:

• Safe access points and fall protection
• Walkways that do not require stepping on modules
• Clear paths around rooftop equipment

7. Fire safety

Electrical systems on roofs must be designed with fire safety in mind: appropriate cable management, isolation points, clearances for firefighting access, and compliance with applicable codes. Discuss requirements with the facility's fire safety advisers and insurer.

8. Electrical integration

The system connects to the facility's electrical network, so check the capacity of the existing switchgear and transformers, the location of the connection point, and the metering arrangement. Metering rules — net or gross — affect how the system should be sized; see net metering vs gross metering.

9. Ownership of the building

If the facility is leased, the landlord's consent is needed, and the remaining lease term matters. A third-party solar provider will also want certainty of roof access for the full contract term.

A pre-design checklist

Before an EPC partner starts detailed design, the facility should be able to provide:

• Structural drawings of the building, if available
• Roof age, material and maintenance history
• Records of any leaks or repairs
• A list of current and planned rooftop equipment
• Single-line diagram of the facility's electrical system
• Recent electricity bills and sanctioned load details
• Building ownership or lease documents

Where drawings are not available, the structural engineer will need to survey the roof and may recommend testing.

Common mistakes

• Installing on a roof due for replacement, then paying to remove and reinstall the system
• Designing the layout without allowing for maintenance walkways
• Ignoring planned future equipment that will later shade the array
• Underestimating wind uplift on roof edges and corners
• Not agreeing responsibility for leaks in the EPC contract
• Assuming a leased building can host a system without the landlord's written consent

During and after installation

Supervise installation closely: walking on fragile roof sheets, over-tightening fixings and poorly sealed penetrations cause problems that only show up later. After installation, inspect the roof and the system together, and again after the first monsoon. Make roof inspection part of the ongoing O&M scope.

When ground-mount or off-site is better

If the roof is weak, fragile, too small or near the end of its life, other options may suit better: ground-mounted solar on spare land within the premises, or off-site supply through open access or group captive arrangements.

How we help

When we assess sites for commercial & industrial solar, structural and roof-condition checks are part of the first screen. We then coordinate qualified EPC partners to carry out the detailed structural assessment, design and installation.