RCC, metal sheet and asbestos are three different jobs
The roof decides the structure, the fixing, the safety plan and the price. What to check on each type before you quote, and when to walk away from one.
Quote the same 50 kW system on a concrete terrace, a trapezoidal sheet shed and an asbestos roof and you have quoted three different projects. The modules are identical. Almost nothing else is.
RCC terrace
The familiar one, and the most forgiving.
What to check: the age and condition of the slab, whether it has been waterproofed and when, existing loads already on it such as water tanks and machinery, and whether the owner intends to build another floor.
How it gets fixed: either ballasted with concrete weights or anchored into the slab with chemical or mechanical fasteners. Anchoring is stronger and lighter but creates penetrations, and each one is a leak path for twenty five years unless it is sealed properly and the sealing is maintained.
The trap: drilling through an existing waterproofing membrane and sealing it casually. The leak shows up in the next monsoon, and it will be attributed to the solar, correctly.
Metal sheet
Most commercial and industrial roofs, and the type where the fixing method matters most.
Trapezoidal sheets are usually clamped or bolted through the crest, never the valley, with a sealing washer, and the fixing must reach the purlin rather than relying on the sheet.
Standing seam is the better case. Non-penetrating clamps grip the seam, so there are no new holes at all. More expensive per clamp, cheaper in risk.
What to check before quoting: sheet gauge and material, age, rust particularly around existing fasteners, purlin spacing and direction, and whether the sheet is still under any roofing warranty. Fixing into somebody's warranted roof can void it, and they will find out later.
Safety: a corroded sheet does not reliably carry a person. Walkways, crawl boards and fall arrest are not optional on an older industrial roof, and the cost of doing that properly belongs in your quotation rather than in your hope that nothing happens.
Asbestos
Be direct about this one: an asbestos cement sheet roof is the type most likely to hurt somebody on your crew.
It is fragile, and it becomes more fragile with age. People fall through asbestos roofs regularly in exactly the circumstance solar installation creates: someone stepping between purlins while carrying something heavy.
It cannot carry point loads. Fixing solar directly to asbestos sheeting is not an acceptable design. Any load has to reach the purlins or a new structure spanning above the sheet.
Cutting, drilling or breaking it releases fibres, which is a health matter with regulatory consequences, not an inconvenience.
Three workable approaches: build an independent structure that transfers load to the purlins or the building frame without stressing the sheet, replace the affected roof area with metal sheeting as part of the project, or decline.
Declining is a legitimate commercial decision. If you proceed, price the safety properly: crawl boards over every working path, fall protection anchored to the structure rather than to the sheet, and a crew that has been told, explicitly, that they may not walk on the sheet.
Tile and sloped domestic roofs
Less common for grid-tied residential in India than a flat terrace, but they appear.
Fixing uses roof hooks that reach the rafter under the tile, with the tile cut or a replacement flashing fitted. The failure mode is the same as everywhere else: a fixing that grips the covering rather than the structure.
The advantage is that tilt and orientation are fixed by the roof, so the design question narrows to which faces are worth using. The disadvantage is that access for cleaning and maintenance is worse, which should shape what you promise in the maintenance plan.
What this means for quoting
Roof type should be a field you capture at the site visit, with a photograph, before anyone prices the job. It determines the structure, the fixing hardware, the safety plan, the labour hours and the risk. It is the single largest source of variation between two apparently identical systems.
That is also why the bill of materials for a sheet roof job looks nothing like one for a terrace, as in bill of materials mistakes that eat a signed job's margin, and why the structural design has to follow the roof rather than a standard drawing, as in the structure is the part that has to last 25 years.
The short version
- RCC: check slab age, existing loads, waterproofing and plans for another floor. Ballast avoids penetrations; anchoring is stronger but must be sealed for the life of the system.
- Metal sheet: fix through the crest into the purlin, never the valley or the sheet alone. Standing seam clamps avoid holes entirely. Check gauge, age, rust and any roofing warranty.
- Asbestos: fragile, cannot carry point loads, and cutting it releases fibres. Span above it, replace it, or decline. Never let the safety plan be the cheap part.
- Tile roofs: hook into the rafter, not the tile, and plan for harder maintenance access.
- Capture roof type with a photograph at the site visit. It drives structure, fixings, safety, labour and risk.
Keep reading
The structure is the part that has to last 25 years
Modules are warranted for decades and the structure holding them often is not. Wind uplift, edge zones, ballast against anchoring, and corrosion near the coast.
One ohm, and the fire that starts in a connector
Earthing is the one thing every DISCOM inspector physically checks, and loose DC connectors are how rooftop systems catch fire. The practice that prevents both.
TOPCon, bifacial, and what actually belongs on a rooftop
TOPCon has taken over Indian rooftop supply and bifacial is sold with it. One of those choices is usually right and the other usually is not, on a house roof.