Solar on a PEB Sheet Roof: Purlin Loads, Clamp Systems, Leaks and Warranties

A PEB sheet roof can usually host solar, but only after four things are checked: the purlin and rafter capacity against the original design loads, the fixing method on your sheet profile, the roof sheet warranty, and wind uplift. Rail-mounted arrays on metal sheet add a modest dead load, but the fixings are where leaks and failures start. Ask for the PEB design report before anyone quotes.

What must the PEB design report show?

A pre-engineered building is designed to a stated set of loads: the dead weight of the sheets and purlins, live load, a collateral load allowance for services hung from the roof, and wind loads for the location. The manufacturer's design report and drawings record these values. They are the starting point for any solar check, because the array adds dead load, concentrates point loads at the fixings and changes how wind pressure acts on the roof.

Our roof load calculator uses a working band of about 12–15 kg per square metre of array for rail-mounted modules on metal sheet. That is a screening figure for dead load only. It does not say whether your purlins can carry it, which depends on their section, spacing, corrosion and the loads already using the capacity. Request the following before the structural check:

• The PEB manufacturer's design report and drawings, with the design code, wind speed and load values.
• The purlin and rafter schedule, and any later additions such as ducts, sprinkler pipes or lighting hung from the roof.
• The sheet profile, thickness, coating and fastener type, and the date of installation.
• The roof sheet supplier's warranty terms and conditions.
• A condition survey: corrosion at laps and fasteners, sagging purlins, ponding, leaks and past repairs.

Where drawings are missing, the engineer needs a measured survey, and sometimes material tests. Our note on putting solar on an existing factory roof sets out the full four-check sequence.

Clamp or through-fix: which system suits which sheet?

The rails should be fixed to the purlins, not to the sheet alone, so the load goes to the steel that was designed to carry it. If your sheet is old, thin or corroded, replace it before the array goes on, because removing and reinstalling modules later costs more than doing it in the right order. For a wider view of how penetrations leak, read roof penetrations and waterproofing.

How do you protect the roof warranty and avoid leaks?

There are two warranties on a PEB roof, and the solar contractor cannot honour either without the other. The sheet supplier's warranty covers the sheet, the coating and sometimes the sealed system, and its terms usually restrict unapproved penetrations, accessories and fixings. The contractor's workmanship warranty covers its own work. Get both in writing, and ask:

• Which fixings, brackets, sealants and rail systems does the sheet supplier accept?
• Does the supplier need to inspect or approve the layout, and is there a fee?
• Who is liable for a leak at a fixing in years one to five, and in the following years?
• Is galvanic contact between aluminium rails or clamps and the sheet's coating addressed?
• Is there an annual inspection of seals in the O&M scope?

An EPC that cannot answer these before the order is likely to discover the answers on the roof.

Wind uplift, expansion and walkways

Wind is often the governing load, not weight. The rooftop specification published on the national rooftop solar portal asks that mounting structures be designed for the wind zone of the location under IS 875 (Part 3), with a factor of safety, and that steel and galvanising meet the relevant Indian Standards. On a roof, edges, corners and ridges see higher pressures than the middle, so the layout, the clamp spacing and the fixing density should vary across the roof, and the design should be shown to you as calculations, not a promise.

Metal roofs also move. Long sheets and long rails expand and contract with temperature, and PEB buildings carry expansion joints that rails should not bridge. Look for slotted holes, sliding clamps where the design calls for them, and breaks in the rail runs at expansion joints.

Finally, safety on the roof. Translucent roof lights are fragile, so the layout must keep modules and walkways clear of them or protect them. Provide a walkway and anchor line for cleaning, keep ridge ventilators and smoke vents free, and route DC cables so they do not rub on sheet edges. See rooftop solar DC fire safety for isolation and firefighter access.

What does it do to the price?

The C&I band we publish is ₹24,000–32,000 per kW excluding GST, and roof type and structure are among the items that move a quote inside it. A sheet roof that passes its check without strengthening is typically a simpler structure than a ballasted RCC system; one that needs purlin reinforcement or re-sheeting carries that cost as a separate line. Ask each bidder to price the roof work, the structure and the leak warranty separately, so you can compare like with like. Our mounting structures and BOS page explains what is in the structure scope.

How Secured Engineers helps

We design the mounting structure in-house and work from your PEB design report with a structural engineer, so that purlin loads, wind uplift and the fixing method are settled before the quote. We file the DISCOM net-metering application and the CEIG approval ourselves, and solar and MEPF can sit under one contract, which helps when roof services, sprinklers and solar share the same purlins. We work from offices in Noida (Delhi NCR) and Ludhiana, with 535+ projects across 18+ states and 89.77% repeat clients.

To start, send us the PEB drawings, a few roof photographs and your bill. Read the mounting structure scope, then message us on WhatsApp, call +91 70099 85817, or ask for a free proposal with the roof check included.