Galvanised steel profiles and purlins: C, Z and U sections
Galvanised steel profiles and purlins are the corrosion-protected structural sections behind roofs, walls, frames and light steel structures, supplied as cold-formed C, Z and U sections, angles and flat bars. ULAMEX supplies galvanised profiles in pre-galvanised structural grades and, where fabrication follows, hot-dip galvanised after making up, to EN 10346, EN 1993-1-3 and EN ISO 1461. This guide covers the section types, the two galvanising routes, grades, standards, purlin systems and use. For the coating detail see our guide to galvanised steel and DX51D.
What galvanised profiles are
A galvanised profile is a structural section carrying a zinc coating for corrosion protection, used wherever steel framing is exposed to weather, damp or condensation. Most are cold-formed: a coil of galvanised strip is roll-formed into a C, Z, U or angle section, so the zinc is already on the steel before the section is made. Heavier or welded sections are galvanised the other way, hot-dip galvanised after fabrication, which dips the finished part in molten zinc. The section shape carries the load and the zinc keeps it from rusting, so the same profile serves outdoors for decades without paint.
Section types
| Section | Use |
|---|---|
| Z purlin | Roof purlins, spanning continuously over rafters with sleeved or overlapped joints |
| C section | Side rails, purlins, studs, floor joists and framing |
| U section | Tracks, channels, edge and framing members |
| Angle | Frames, brackets, supports and bracing |
| Flat bar | Straps, ties, cleats and edge members |
Z and C sections are the workhorse purlins and rails of steel-framed buildings, U sections form tracks and channels, and galvanised angle and flat bar handle framing, bracing and supports.
Pre-galvanised and hot-dip galvanised
The two galvanising routes suit different sections, and the choice affects the coating and the fabrication.
| Route | Character |
|---|---|
| Pre-galvanised (mill coil) | Zinc applied to the strip before roll-forming; even, thin coating; ideal for cold-formed purlins and studs |
| Hot-dip after fabrication | Finished part dipped in molten zinc to EN ISO 1461; thick 45 to 85 micron coating; covers welds and cut ends |
Cold-formed purlins and studs use pre-galvanised strip, which gives a clean, consistent coating and an economical section. Where sections are welded up or need the heaviest protection, hot-dip galvanising after fabrication coats the whole part, welds and all, at 45 to 85 microns to EN ISO 1461.
Grades and coating
Cold-formed profiles are rolled from structural galvanised strip, and the grade sets the strength.
| Grade or coating | Detail |
|---|---|
| S250GD to S450GD | Structural galvanised strip grades to EN 10346; the number is the minimum yield in MPa |
| S235JR / S355J2 | Carbon base for sections hot-dip galvanised after fabrication |
| Z275 (pre-galvanised) | The general coating weight for cold-formed sections, in grams per square metre |
| 45 to 85 microns (hot-dip) | Coating thickness after galvanising to EN ISO 1461 |
Purlins are typically rolled from S350GD or higher for the strength to span, while framing and studs use lighter grades. State the section, size, grade and galvanising route with an enquiry so the profile matches the load and the exposure.
Standards
| Standard | Scope |
|---|---|
| EN 10346 | Continuously hot-dip coated strip, the feedstock for cold-formed sections |
| EN 1993-1-3 | Eurocode 3 design of cold-formed steel members and sheeting |
| EN ISO 1461 | Hot-dip galvanised coatings on fabricated steel, coating thickness |
| EN 1090-1 EXC2 | Execution of steel structures, held by ULAMEX with welding to ISO 3834-2 |
A galvanising certificate stating the coating and a 3.1 inspection certificate are supplied on request, so the section is documented against the structural design and the CE marking route.
Purlin systems
Purlins carry the roof and wall sheeting between the main frames, and the section is chosen for the span and the layout. Z sections nest and overlap, so they run continuously across several supports with sleeved or overlapped joints that carry the bending over the rafters efficiently. C sections butt at each support and suit single spans, side rails and framing. Both are fixed with bolts or self-drilling screws and tied with anti-sag rods and cleats, and the galvanised finish means the roof structure needs no maintenance painting over its life.
Sizes and how to specify
A purlin is specified by its section type, depth, gauge (the material thickness) and grade, with the depth and gauge set by the span and the roof load. A deeper section or a thicker gauge carries a longer span or a heavier load, so the roof geometry drives the choice. C and U sections are specified the same way, by depth, flange and gauge. Give the section type, depth, gauge, grade and length with an enquiry, along with the span and load where the desk is to advise, and state the galvanising route and coating class, so the profile matches the structural design.
Cleats, sleeves and sag rods
A purlin run is more than the sections. It is completed with cleats that bolt the purlin to the rafter, sleeves that join Z sections over a support to make the run continuous, and anti-sag rods or bars that tie the purlins at mid-span to stop them twisting under load. Side rails add similar accessories for the walls. Sourcing the sections, cleats and sag system together keeps the galvanised coating consistent across the whole roof and wall structure and simplifies the delivery.
Applications
Galvanised profiles frame and support across light construction. Z and C purlins carry roof and wall cladding on industrial, agricultural and commercial buildings. C sections and U tracks build steel-framed walls, floors, mezzanines and partitions. Galvanised angle and flat bar form brackets, bracing, supports and cleats. Solar and canopy structures use galvanised sections for the outdoor frame. Fencing, gates and gratings use galvanised sections and bar. In each case the zinc lets the structure stand in damp, exposed or condensation-prone spaces without rusting.
Fabrication and connections
Galvanised sections are bolted, screwed and welded into frames. Cold-formed purlins and studs are joined with bolts and self-drilling screws that need no drilling of pilot holes, which keeps the coating intact. Where a pre-galvanised section is drilled or welded, the exposed steel is re-protected with a zinc-rich paint, since the small bare area is otherwise not covered; hot-dip galvanising after fabrication avoids this by coating the finished part. Welding to EN 1090 uses a qualified procedure, and ULAMEX holds EN 1090-1 EXC2 with welding to ISO 3834-2 for certified structural fabrication.
Galvanised profiles versus alternatives
Galvanised profiles are the economical corrosion-protected choice for light structural framing. Against uncoated carbon sections they need no paint outdoors; against stainless sections they are far cheaper where the zinc coating gives enough corrosion resistance; against aluminium sections they are stronger and cheaper but heavier. For the heaviest structures, hot-rolled carbon sections galvanised after fabrication are used, and for severe corrosion or appearance, stainless is specified. ULAMEX supplies galvanised profiles alongside carbon, stainless and aluminium sections, so a project sources the full frame from a single supplier.
Galvanised steel profiles from ULAMEX
ULAMEX has supplied steel since 1988, and galvanised profiles are a core part of the range.
| What you get | Detail |
|---|---|
| Sections | Cold-formed C, Z and U sections, angles and flat bars |
| Grades | Structural galvanised strip S250GD to S450GD; S235JR and S355J2 base for hot-dip |
| Galvanising | Pre-galvanised Z275, or hot-dip after fabrication 45 to 85 microns to EN ISO 1461 |
| Standards | EN 10346, EN 1993-1-3, EN ISO 1461; EN 1090-1 EXC2 with welding to ISO 3834-2 |
| Terms | 3.1 and galvanising certificate on request, no minimum order on stocked SKUs, dispatch 2 to 7 working days |
Need galvanised profiles or purlins for a project? Send the section, size, grade and galvanising route, and ULAMEX will return a non-binding quotation. See our guides to galvanised steel sheet and structural steel grades, and our supply capabilities, or contact the export desk at [email protected] or +48 504 424 761.
Frequently asked questions
What is the difference between C and Z purlins?
Z sections nest and overlap, so they run continuously over several supports with sleeved joints, which is efficient for multi-span roofs. C sections butt at each support and suit single spans, side rails and framing.
What is the difference between pre-galvanised and hot-dip galvanised sections?
Pre-galvanised sections are roll-formed from strip that was zinc coated at the mill, giving an even, thin coating ideal for cold-formed purlins. Hot-dip galvanising dips the finished part in molten zinc to EN ISO 1461, giving a thick 45 to 85 micron coating that covers welds and cut ends.
What grades are galvanised profiles rolled from?
Structural galvanised strip grades S250GD to S450GD to EN 10346, where the number is the minimum yield in MPa. Purlins are typically S350GD or higher for the strength to span, while framing and studs use lighter grades.
What standard is used to design cold-formed purlins?
EN 1993-1-3, the Eurocode 3 part for cold-formed steel members and sheeting, which covers local and distortional buckling of the thin section. The strip follows EN 10346 and hot-dip galvanising follows EN ISO 1461.
Do drilled or welded points on a galvanised section need protecting?
Yes. Where a pre-galvanised section is drilled or welded, the small area of exposed steel is re-protected with a zinc-rich paint. Sections hot-dip galvanised after fabrication avoid this because the whole finished part is coated.
How is a purlin size chosen?
By the span and the roof load: a deeper section or a thicker gauge carries a longer span or a heavier load. Give the span and load with the section type and the desk will advise on the depth and gauge, or supply to your structural engineer’s schedule.
Are the sections certified for structural steelwork?
Yes. A galvanising certificate and a 3.1 inspection certificate are supplied on request, and ULAMEX holds EN 1090-1 EXC2 with welding to ISO 3834-2, so sections are ready for certified structural fabrication.