IS 277:2018 is the Indian Standard (BIS) for galvanized steel sheets (plain and corrugated). IS 277 specifies galvanized (zinc-coated) steel sheets in plain and corrugated form. GI sheets are the most widely used roofing material in India. The standard defines zinc coating mass (determines corrosion life), mechanical properties, and dimensional requirements.
Specification for zinc-coated (galvanized) plain and corrugated steel sheets covering grades, coating mass, mechanical properties, dimensions, and testing.
Key reference values — verify against the current code edition / project specification.
| Reference | Value | Clause |
|---|---|---|
| Subject | Zinc-coated plain & corrugated steel sheets | Scope |
| Coating class | Total zinc-coating mass class (g/m², both faces) | Classes |
| Grades | By yield strength / forming grade | Grades |
| Tests | Coating mass, adhesion (bend), tensile, dimensions | QC |
| Use | Roofing/cladding, ducts (IS 655), flashings | Application |
| Read with | IS 2629/IS 4759 (galvanizing) / IS 655 | Cross-ref |
BIM-relevant code. See the BIM Hub for ISO 19650, IFC, and LOD/LOIN frameworks used alongside it.
IS 277:2018 is the Indian Standard for Galvanized Steel Sheets (Plain and Corrugated) — Specification. It covers hot-dip galvanized (HDG) steel sheets used for roofing, cladding, ducting, tank construction, fencing, structural cold-formed sections, automotive panels, and countless other engineering applications.
Use it when: - Specifying GI sheets for industrial / warehouse roofing (the iconic 'tin shed' is GI corrugated sheet) - Procuring HVAC duct material — galvanized sheet is standard for low-pressure rectangular and round ducts per IS 655 / SMACNA - Cold-formed structural sections (purlins, girts, cable trays, light steel framing) — IS 811 covers profiles, IS 277 covers the parent sheet - Auditing galvanized coating on procured sheet — coating mass per unit area, adhesion, uniformity - Investigating premature corrosion — most GI failures trace to coating mass below specification
This is one of the highest-volume steel codes in Indian construction — millions of tonnes of GI sheet consumed annually. Procurement quality varies enormously across manufacturers.
Two thickness categories: - Plain galvanized sheets: 0.14 to 4.0 mm nominal - Corrugated galvanized sheets: 0.40 to 1.60 mm nominal (corrugation forms specified in IS 277 Annex C — typical pitches 76 mm and 145 mm)
Coating mass designations (Clause 4.4) — total mass of zinc per square metre, both faces combined:
| Class | Min coating (g/m², both faces) | Typical thickness (μm, each face) | |---|---|---| | Z120 | 120 | ~9 | | Z180 | 180 | ~13 | | Z200 | 200 | ~14 | | Z275 | 275 | ~19 | | Z350 | 350 | ~25 | | Z450 | 450 | ~32 | | Z600 | 600 | ~43 |
Typical specifications in Indian practice: - Roof / wall cladding (industrial): Z275 to Z350 (lasts 15-25 years in inland climate, 8-15 years in coastal) - HVAC ducts (internal): Z120 to Z180 (low-corrosion environment, lasts 30+ years) - Fencing, light structures: Z200 - Marine / aggressive industrial: Z450 to Z600 (or specify pre-painted Z275 + polyester coat) - Automotive body: Z100 to Z140 (typically pre-painted)
Coating-mass test (Annex D): chemical method — strip the coating with HCl + dezincification inhibitor; weigh sheet before and after. Difference divided by sheet area gives g/m². Standard sample size 50 × 50 mm or 100 × 100 mm.
Adhesion test (Annex E): bend sheet over a mandrel of specified diameter (typically equal to sheet thickness); check that the coating does not flake or crack on the outer (tension) side.
Mechanical properties (Clause 6 + Annex G): - Tensile strength, yield, elongation depend on the steel grade (CR3, CR4, CR5 commercial; or structural HSLA grades) - For pre-cold-rolled commercial: yield ≥ 240 MPa, elongation ≥ 22% - For structural grades: yield ≥ 300-550 MPa per Annex G - Tested per IS 1608 Part 1:2005
Sheet sizes: 1000-1500 mm wide, 1500-3000+ mm long; thickness 0.14, 0.18, 0.20, 0.25, 0.30, 0.35, 0.40, 0.45, 0.50, 0.60, 0.71, 0.80, 0.90, 1.00, 1.20, 1.60, 2.00 mm (common). Thickness tolerance ± 5% per IS 1956 Part 6.
Most common procurement failure: a sheet sold as 'Z275' actually carries Z120-Z150 coating. The contractor saves ~₹15-20/kg on coating; the customer loses 50-60% of the sheet's design life.
Why this is so common: zinc is ~70% of the value-add in galvanized sheet (raw steel is ~₹50/kg, zinc coating adds ~₹15/kg, formal galvanized sheet sells at ₹75-90/kg). A dishonest supplier ships sheet with thinner coating and pockets the savings. The visual appearance (silvery sheen, spangle pattern) is identical at Z120 and Z275 to an untrained eye.
How to catch this on site: 1. Coating-mass test at independent lab per Annex D — costs ₹500-1500 per sample, takes 1-2 days. Mandatory for any supply > 5 tonnes. 2. Magnetic coating thickness gauge (Elcometer 456 or equivalent) — non-destructive, measures one face at a time. ₹15,000-40,000 for the gauge. Reads in μm; multiply by 7.13 g/m²·μm to get coating mass per face. Total mass = sum of both faces. 3. Visual check — heavier coating tends to have larger zinc 'spangles' (snowflake patterns from molten zinc cooling). Z275+ shows clear spangles; Z120 often appears uniformly dull/grey. Not foolproof but a quick screen.
Brand reality: BIS-licensed major manufacturers (Tata Steel, JSW, Essar, Bhushan, Jindal, JSW Vallabh) deliver IS 277 conformance consistently. Tier-2 / unbranded GI sheets are a quality lottery — 30-40% of random samples typically fall below stated coating mass. For projects > ₹20 lakh of GI sheet value, mandate BIS-licensed branded supply with batch-level Coating Mass Test Certificates.
1. Specifying thickness without coating mass — 'I want 0.5 mm GI sheet' tells the supplier nothing about the coating. Always specify both: '0.50 mm thick, Z275 coating per IS 277:2018'. Without coating spec, supplier defaults to cheapest available.
2. Using Z120 in coastal locations — coastal Mumbai, Chennai, Vizag, Kochi require Z350 minimum to survive 15+ years. Z120 in coastal exposure rusts within 3-5 years. Match coating mass to environment.
3. Cut edges and drill holes left bare — when sheet is cut or drilled, the steel edge is exposed (no zinc coating on the cut face). For exterior applications, brush a zinc-rich paint (cold galvanizing) on all cut edges and around holes. Skipping this causes rust streaks within 1-2 years.
4. Galvanic coupling with aluminium/copper fasteners — galvanized sheet + non-Zn fastener in damp environment = galvanic cell; the zinc coating sacrifices first, exposing steel. Use galvanized steel screws with GI sheet, or stainless A2/A4 if dissimilar metals are unavoidable.
5. Skipping the adhesion check — over-aged or poorly-processed coatings can be 'brittle' and flake off on bending. The mandrel bend test (Annex E) catches this. Useful when sheet is to be roll-formed into corrugations or purlins after delivery — failure happens at the cold-forming roller, not in storage.
6. Using IS 277 sheet for sheltered indoor partition systems where pre-painted GI (PPGI) is cheaper-and-better — for visible interior surfaces (raised access floors, modular partitions, HVAC casings), pre-painted galvanized sheet per IS 14246 has factory-baked coating that is more uniform, more durable, and ready for paint without site primer. Don't over-specify.
IS 277:2018 is the current revision (replacing IS 277:2003) and is well-aligned with international practice (ASTM A653 / EN 10346). The 2018 revision: - Standardized coating-mass designations as Z120, Z180, Z200, Z275, Z350, Z450, Z600 (replacing older designations) - Added higher-strength structural grades (yield 500-550 MPa) for HSLA cold-formed applications - Clarified adhesion test geometry and acceptance - Improved chemistry tolerances for HSLA grades
Indian market reality: - Major brands (Tata Steel BSL, JSW Steel, Jindal) supply IS 277:2018 with consistent quality. CTCs are reliable. - Tier-2 manufacturers (smaller pickling-galvanizing units in Punjab, Gujarat, TN) often supply 'IS 277'-stamped sheet with actual coating 50-70% of stated value. Mandate batch testing. - Imported sheet (China, Korea) — generally good quality if from recognized mills (Baosteel, POSCO, JFE) but may carry ASTM/EN designations instead of IS. Translate using equivalence tables.
Coating choice by application — practical defaults: - Industrial roofing, inland: Z275 + occasional washing - Industrial roofing, coastal: Z450 minimum, or PPGI (IS 14246) with PVDF topcoat - HVAC ducts, indoor: Z120 is fine - Cable trays, indoor: Z200 - Cable trays, outdoor: Z350 or hot-dip galvanized after fabrication (IS 4759, separate code) - Light-gauge wall framing (LGSF): Z275 minimum; Z350 for permanent wall systems
Cost trade-off: doubling coating mass (Z180 → Z350) typically doubles service life (8 years → 16 years) for a ~12-18% sheet cost premium. The cost-of-replacement (sheet + labour + downtime) usually justifies the premium. Specify generously.
| Parameter | IS Value | International | Source |
|---|---|---|---|
| Standard roof coating | Z275 = 275 g/m² | Z275 = 275 g/m² | EN 10346 |
| ASTM equivalent | Z275 = 275 g/m² | G90 = 275 g/m² (0.90 oz/ft²) | ASTM A653 |