Kumar IronUpdated
In this guide
The four materials in one line each
- GI (galvanised iron): zinc coated steel, plain silver look. Budget friendly and widely used.
- Colour coated (PPGI or PPGL): steel with zinc or zinc aluminium plus a paint system. Better looks and longer life.
- Polycarbonate: a clear or tinted plastic sheet, flat, corrugated or multiwall. Lets light in.
- Translucent FRP: fibreglass reinforced plastic sheets in the same profile as metal sheets, used as skylights within a metal roof.
Side by side
| Property | GI | Colour coated | Polycarbonate | FRP skylight |
|---|---|---|---|---|
| Cost direction | Lowest of metals | Higher than GI | Higher than metal sheets | Moderate, used in small areas |
| Life (typical) | Medium, depends on zinc | Longer, depends on coating | Long if UV protected | Medium, can yellow over time |
| Heat | Gets very hot | Cooler in light colours | Traps heat unless tinted or multiwall | Lets in heat with light |
| Rain noise | Loud | Loud | Loud on thin sheet, quieter multiwall | Moderate |
| Light | None | None | High | High |
| Strength | Good | Good | Good impact, can scratch | Brittle with age |
Cost direction is only a comparison, not a price. Rates change, so call or WhatsApp the store for the day's rate.
Polycarbonate: what to check
Not all polycarbonate is equal. Cheap sheets without a UV protective layer turn yellow and brittle in a couple of years under Indian sun. Ask that the UV protected side is marked and fitted facing the sky. Thickness matters: thin 1 mm solid sheets flex and rattle, while multiwall sheets (with hollow channels) insulate better and are quieter.
Polycarbonate also expands more than steel with heat. Use the right profile accessories and leave room for movement rather than driving screws tight. Do not use harsh solvent cleaners, and wash with water and mild soap.
Translucent FRP and skylights in a metal roof
A common smart approach is to roof mostly in metal and replace a few sheets with translucent FRP or polycarbonate of the same profile. This cuts daytime lighting costs in godowns, workshops and factories without turning the whole roof into a greenhouse. Keep the skylight area modest. A small share of the roof, spread along the length, usually gives enough light. Too much glazing makes the building hot.
Fix skylight sheets with the same pattern as metal sheets, and seal laps carefully, since these are the first spots to leak.
Which one for which place
| Place | Good choice | Why |
|---|---|---|
| Cattle or dairy shed | Colour coated or GI with high zinc coating, light colour | Handles ammonia better, cooler in light shades |
| Factory or godown | Colour coated plus a few FRP skylight sheets | Durable, daylight where needed |
| Terrace shed or parking | Polycarbonate or colour coated | Polycarbonate gives light, colour coated gives longer life |
| Temporary or low budget cover | GI | Lowest cost direction |
| Courtyard or passage with light | Multiwall polycarbonate | Light with less heat and noise |
For heat and noise problems under any metal roof, see our separate guide on cooling a tin roof.
Frequently asked questions
- Is polycarbonate better than a tin sheet?
- It depends on the need. Polycarbonate gives light but can trap heat. Metal sheets last long and cost less per area but give no light. Many roofs use both.
- Does polycarbonate turn yellow?
- Cheap, non-UV-protected sheets do. Buy sheets with a UV protective layer and fit that side facing up.
- How much skylight should a factory roof have?
- A small share of the roof area, spread out along the length, is usually enough. Too much glazing causes heat. Your designer can fix the exact share.
- Which is better for a cattle shed, GI or colour coated?
- Colour coated in a light shade with good coating usually lasts longer and runs cooler. A high zinc GI sheet is a budget option. Ask the store which coating classes are available.