The structure is the part that has to last 25 years

Every rooftop proposal in India quotes a twenty five year module warranty. Very few say anything about the structure, which is the component most likely to fail first and the only one whose failure can injure somebody.

Wind is the load that decides it

Dead weight is easy. Wind is not, because a tilted module is a wing.

Air moving across an inclined array generates uplift, and on a rooftop the effect concentrates in specific places:

• Edges and corners. The zones along a roof's perimeter, and especially at corners, see significantly higher local pressures than the middle of the roof. An array laid uniformly to the parapet is most vulnerable exactly where installers most often push it.
• The first row. Wind hitting the leading edge of an array gets under it. Rows behind are partly sheltered.
• Higher tilt, higher uplift. The tilt that maximises annual yield is not always the tilt the structure and the site should carry.

Indian wind design follows IS 875 Part 3, which maps basic wind speeds across the country, ranging from the mid thirties of metres per second inland to the fifties along the cyclone exposed eastern and western coasts. That map is why a structure specification that works in Bengaluru is not automatically adequate in Bhubaneswar.

Ballast or anchor

Two ways to keep an array on a flat roof, and the choice has consequences beyond the structure.

Ballasted systems resist uplift with weight, usually concrete blocks. No penetrations, so no new leak paths, and it is quick. The cost is dead load: on an older RCC roof, several kilograms per square metre extra is a structural question, not a detail. It is also only as good as the ballast calculation, and ballast blocks have a habit of being "adjusted" on site.

Anchored systems bolt into the structure. Stronger and lighter, and it creates penetrations that must be sealed properly and stay sealed for twenty five years. On a sheet roof, anchoring into the purlin rather than the sheet is the difference between a fixing and a hole.

The wrong answer is a ballasted design that was quietly under-ballasted because the blocks were heavy to carry up.

Corrosion is the slow failure

A structure does not usually fail in a storm on day one. It fails because it corroded for eight years first.

Three things decide how long it lasts:

• Galvanising. Thickness matters, and the specification should state it rather than saying "GI".
• Fasteners. Stainless where the environment demands it, and never mixed metals in contact without isolation.
• Cut edges. Every field cut exposes bare steel. Either avoid site cutting or treat the cut.

Within thirty kilometres of the coast, this stops being a maintenance question and becomes a design one, in the same way module selection does. The CEA's 2026 technical standards, effective April 2027, add salt mist testing for modules in highly corrosive environments and a twenty five year design life for solar plants, which is in new CEA standards land in April 2027.

The roof underneath

Before any of this, someone has to answer whether the roof can carry the system at all.

For residential RCC, an experienced installer's judgement plus a look at the age, span and condition is usually accepted practice. For anything commercial, and for any older or unusual building, a structural engineer's opinion is worth its small cost, and increasingly tenders require it in writing.

Specific things to look at: the age and condition of the slab or sheet, existing water tanks and equipment already loading it, whether the roof has been waterproofed and how recently, and whether any future floor is planned. That last question has cancelled more commercial installations at the last minute than any technical issue.

What belongs in the proposal

Four lines, which almost no residential quotation carries and every commercial one should:

• Structure material and galvanising specification, stated.
• Design wind speed used, and the standard it follows.
• Fixing method: ballasted or anchored, and how penetrations are sealed.
• Height above the roof surface, because it determines shading clearance and cleaning access.

Those four lines are also your defence when a customer compares your price to someone using thinner sections and fewer fixings. Without them, both quotations look like "mounting structure" on a line item, and the cheaper one wins.

The short version

• Wind uplift, not dead weight, sets the structural design. Edges, corners and the first row see the highest local pressures.
• Indian practice follows IS 875 Part 3, with basic wind speeds varying widely between inland and cyclone exposed coasts.
• Ballasted means no penetrations but added dead load, and depends on the ballast actually being placed. Anchored is stronger but creates penetrations that must stay sealed.
• Corrosion is the slow failure: state galvanising thickness, use appropriate fasteners, treat every field cut.
• Get a structural opinion for commercial roofs and older buildings, and ask whether another floor is planned.
• Put material, design wind speed, fixing method and structure height in the proposal.