Kumar IronThe main types of roofing sheet
- Colour coated sheets: steel sheet with a zinc or zinc-aluminium coating, then primer and a coloured paint layer on top. The most common choice for houses, shops and sheds today.
- GI sheets (galvanised iron): steel with a zinc coating only, usually plain grey and corrugated. Cheap, strong, and the traditional choice for sheds and cattle sheds.
- GC sheets (galvanised corrugated): the same GI sheet rolled into a corrugated profile. People often say GI and GC for the same thing.
- Galvalume (bare aluminium-zinc coated) sheets: steel with a 55% aluminium zinc coating. Better rust resistance than plain GI, and the usual base under good colour coated sheets.
- Cement and fibre sheets: the familiar grey corrugated sheets made of cement with fibres. Cheap and cool but brittle.
- Polycarbonate sheets: clear or tinted plastic sheets used for skylights, verandahs, car parks and greenhouses.
Side by side comparison
| Type | Heat inside | Rain noise | Typical life | Cost tier |
|---|---|---|---|---|
| Colour coated (galvalume base) | Moderate, better with light colours | High without insulation | 20 to 30 years | Medium to high |
| Plain GI / GC | Hot | High | 10 to 15 years | Low to medium |
| Bare galvalume | Moderate, reflects well when new | High | 20 to 25 years | Medium |
| Cement / fibre | Cooler | Low | 15 to 25 years if not broken | Low |
| Polycarbonate | Hot unless tinted or UV coated | Medium | 10 to 15 years | Medium to high |
| Puff / sandwich panel | Coolest | Lowest | 20 years and more | Highest |
Life depends heavily on coating thickness, sheet thickness, slope, fixing and how close you are to smoke, chemicals or animal sheds. Treat these as typical ranges for inland north India.
Heat: the big issue in UP summers
Any thin metal sheet passes heat quickly. On a May afternoon an unprotected dark sheet roof makes a room very hot. You can manage this in three ways. Choose a light colour such as white, off white or light grey, which reflects much more sun than dark red or blue. Leave a good air gap with ventilators at the ridge. Or use an insulated option: a sheet with a foam or glass wool layer underneath, or a puff (sandwich) panel for rooms where people live or work all day.
Cement sheets stay cooler than plain metal, which is why they remain popular for godowns and cattle sheds on a tight budget.
Noise in the monsoon
Metal sheets drum loudly in heavy rain. For a shed or godown this hardly matters. For a shop, classroom or living space it does. Insulation under the sheet, a false ceiling, or a puff panel cuts noise a lot. Cement sheets are naturally quieter. Polycarbonate sits in between.
Life and rust
Rust is what ends a metal roof. The protection comes from the coating, not the steel. Zinc-aluminium (galvalume) coatings last much longer than plain zinc, which is why branded colour coated sheets on a galvalume base outlast cheap GI. When comparing sheets, ask for three things: base metal thickness (for example 0.40 or 0.50 mm), coating type and weight (for example AZ150 for galvalume), and the brand's warranty.
Cement sheets do not rust, but they crack if someone walks on them, and old asbestos cement sheets should not be cut or drilled without protection. Modern sheets are asbestos free, but check the label.
Cost tiers, without the price tags
Rates move every week with steel and zinc prices, so we compare by tier. Call us for today's rate.
- Lowest: cement and fibre sheets, then plain GI / GC of thin gauge.
- Middle: bare galvalume, and colour coated sheets of 0.35 to 0.40 mm.
- Upper: branded colour coated sheets of 0.45 to 0.50 mm with heavy coating, and good quality polycarbonate.
- Highest: puff or sandwich insulated panels.
Remember that thicker sheets need fewer purlins and survive storms better, so the cheapest sheet is not always the cheapest roof.
Which sheet should you pick?
- House top floor room or shop: light coloured colour coated sheet of 0.45 to 0.50 mm, with insulation or a false ceiling below.
- Factory or warehouse shed: colour coated or galvalume sheets, with ridge ventilators and a few polycarbonate sheets for daylight.
- Cattle shed or budget godown: cement sheets for coolness, or GI sheets if you want strength against breakage.
- Verandah, car park or terrace cover: polycarbonate for light, or colour coated if you want shade.
- Office or room on a terrace that people use all day: puff panel.
Fixing tips that make the roof last
- Keep a minimum slope as the sheet maker recommends, usually around 1 in 10 for profiled metal sheets.
- Use self drilling screws with EPDM washers, not nails, and fix at the crest of the profile.
- Give at least one corrugation side lap and a proper end lap on long roofs.
- Cut with a nibbler or shears, not a grinder, which burns the coating and starts rust at the edges.
- Sweep away metal swarf after drilling. Left on the sheet, it rusts and stains the paint.
Frequently asked questions
- Which roofing sheet is best for a house in hot weather?
- A light coloured colour coated sheet of 0.45 to 0.50 mm with insulation below, or a puff panel if the room is used all day. Plain dark sheets without insulation make rooms very hot in summer.
- Is colour coated sheet better than GI sheet?
- For most uses, yes. A good colour coated sheet on a galvalume base resists rust longer, looks better and reflects more heat. GI sheets are cheaper and fine for sheds where looks and heat matter less.
- How long does a colour coated roofing sheet last?
- A branded sheet with a proper zinc-aluminium coating usually lasts 20 to 30 years inland, if fixed correctly with good screws and cut without a grinder.
- What thickness of roofing sheet should I buy?
- 0.40 to 0.50 mm for homes, shops and sheds. Thinner sheets dent easily and need closer purlins. Always check the base metal thickness, not the total thickness with paint.