Solar on a sheet or tile roof? Check the roof before the panels.

Most solar advice assumes a flat concrete roof.

Plenty of Bengaluru homes do not have one. Older independent houses, sheds and some commercial buildings sit under metal sheets, asbestos-cement sheets or clay tiles. Rooftop solar can still work on these, but the questions are different from a flat terrace. Here is what to check before you sign.

First question: can the roof carry it?

A solar array adds dead weight, and it adds wind load. Panels act like a sail in a strong gust, so the force pulls upward as well as pressing down. On a flat RCC slab the structure is bolted into a strong base. On a sheet roof, the sheet itself is rarely the strong part. The load has to reach the purlins or rafters underneath.

• Ask who inspects the roof structure, and ask for the finding in writing. A site visit that only measures the area is not a structural check.
• Old or corroded sheets, rusted purlins and cracked tiles are a reason to repair or replace the roof first, not to bolt panels on top.
• If the roof will need replacing soon, do it first. Removing and refitting an array later is an extra cost.

For anything beyond a simple shed, a qualified structural engineer's opinion is cheap compared with a damaged roof. This is a list of questions, not engineering advice.

How panels are usually fixed to each roof type.

• Metal sheet roofs: mounting rails are commonly clamped or fastened to the sheet ribs or to the purlins. Clamp-on fittings avoid drilling through the sheet, and each drilled hole is a place for water to enter. Ask which method is proposed and what seals each fastener.
• Asbestos-cement sheets: these are brittle and should not be walked on or drilled casually. Disturbing them raises a health concern as well as a leak concern. Ask the installer how they plan to work on them, and consider a proper roof replacement first. Check current official guidance on handling these sheets.
• Clay or Mangalore tiles: tiles crack under foot. The usual approach is special hooks that sit under the tile and attach to the rafter. Ask who replaces a tile that breaks, and make that part of the agreement.
• Sloped roofs generally: panels fixed parallel to the slope are simpler than tilted frames. A steep slope facing away from the sun costs you output. Our note on shading helps you judge a site.

Leaks: the part owners worry about, rightly.

The risk on a sheet or tile roof is the fixing, not the panel. Insist that the work order names the fixing method, the sealing method and who is responsible for any leak that appears after installation. A rooftop that never leaked before should not start leaking because of a solar contract. The same principle applies to a flat roof, covered in our note on waterproofing and mounting structures.

Access, cleaning and cable routing.

• Maintenance access: sheet roofs can be slippery, especially after rain, and fragile in places. Ask how panels will be cleaned safely and whether a walkway or anchor point is part of the design. See cleaning and maintenance.
• Cable routing: cables should be clipped and protected from sharp sheet edges and sun, and should not rest in pooling water. Entry points into the building need sealing.
• Earthing: a metal roof that carries panel frames needs proper earthing. Read our note on earthing and surge protection.

A simple cost check, with illustrative numbers.

Say a 3 kW system on a flat terrace is quoted at an illustrative Rs 1,80,000. A sloped sheet roof may add costs for special fixings, a structural check, walkways or roof repairs. Suppose those add Rs 20,000. That is not a rule. Ask for any extra items to be listed line by line so you can compare quotes. Our note on comparing quotes explains how.

If your roof is not suitable.

There are alternatives. A ground-mounted array in an open compound, or a new light steel structure built specifically for the panels over a courtyard or parking area, can work where the roof cannot. Both need space and BESCOM approval, so confirm with your installer first.

Quick FAQ.

Does a tiled or sheet roof affect BESCOM net metering? The roof type does not change the process, which still depends on your sanctioned load and meter. See our sanctioned load note.

Will the warranty cover roof leaks? Panel and inverter warranties normally do not cover your roof. That is why the workmanship terms in the work order matter.