Z & C Purlin Buying Guide: Galvanized Cold-Formed Steel Purlins for Roof and Wall Structures
In a steel-frame building, the members you rarely see do the quiet work: purlins carry the roof and wall cladding loads across to the main beams. The two profiles buyers specify are Z purlins and C purlins — cold-formed from galvanized steel strip. Pick the wrong section, thickness, or zinc coating and the roof sags, the cladding rattles, or the purlin rusts before the building is paid off.
This guide compares Z vs C, the dimensions that matter, coatings, and a complete RFQ checklist.
What Are Z and C Purlins?
Both are cold-rolled from galvanized steel coil into a channel-like section with a small inward lip on each flange for stiffness. A C purlin is a single C (or U) section; a Z purlin has a Z (or haunch) shape so that two sections can overlap at a splice and lie flush. That overlap is why Z purlins are preferred for continuous spanning roofs.
Z vs C: Which to Choose
| Aspect | C Purlin | Z Purlin |
|---|---|---|
| Splice | Butt joint, needs plates | Overlap splice, flush |
| Continuous span | Less efficient | Efficient (roofs) |
| Walls | Common | Common |
| Redundancy / handling | Simple | Slightly more care |
Rule of thumb: use Z for roof (continuous, overlapping runs) and C for walls and shorter spans, though both are used interchangeably on many projects.
Key Dimensions
- Depth (web height): 100–300 mm typical; deeper carries longer spans.
- Flange width: 40–80 mm; wider gives better cladding screw purchase.
- Lip height: 15–25 mm for torsional stiffness.
- Thickness: 1.5, 1.8, 2.0, 2.5, 3.0 mm (galvanized).
- Length: cut to project requirement, often 6–12 m.
Material and Coating
Purlins are formed from continuously hot-dip galvanized coil. Specify:
- Base steel: structural grade such as S350 / S450 GD (EN 10346) or equivalent.
- Zinc coating: Z150–Z275 g/m²; Z275 for aggressive or coastal sites.
- Yield strength: higher grades (S450) allow thinner sections.
| Coating | Protection | Use |
|---|---|---|
| Z150 | Moderate | Dry inland buildings |
| Z225 | Good | General industrial |
| Z275 | High | Coastal, humid, corrosive |
Standards and References
- EN 10346: continuous hot-dip coated steel for cold forming.
- EN 1090: execution of steel structures (CE marking).
- ASTM A653 / A1003: US coating and structural sheet specs.
- EN 1993: design of steel structures (section checks).
Holes, Cuts, and Connections
Most buyers receive pre-punched purlins: bolt holes for cleats, web holes for services, and mitre or swage cuts at apex for a clean overlap. Confirm:
- Hole pattern and diameter (usually M12 / 14 mm).
- End cuts (square, mitred, sleeved).
- Cleat / bracket supply if needed.
Common Applications
- Industrial sheds, warehouses, workshops.
- Roof and wall secondary framing.
- Solar panel mounting sub-structure.
- Canopies, mezzanines, agricultural buildings.
RFQ Checklist: What to Send Your Supplier
- Profile: Z or C, with section drawing
- Depth × flange × lip × thickness (mm)
- Yield grade and zinc coating (e.g., S350GD Z275)
- Lengths and quantities (per size)
- Hole pattern / end cuts required
- Single length or sleeved spans
- Packing and destination port / Incoterm
FAQ
Z or C for my roof? Z for long continuous roof runs (overlap splice); C for walls and simple spans.
How thick for a 6 m span? Typically 1.8–2.5 mm depending on load; send the span and load and we size it.
Z275 or Z150? Z275 for coastal/humid; Z150 for dry inland only.
Why Source Purlins from Yihang Metal
Yihang Metal roll-forms galvanized Z and C purlins to your section drawing in S350/S450 GD steel with Z150–Z275 coating, pre-punched and cut to length, supplied with cleats on request. We work to EN 10346 / EN 1090, provide MTCs, and support third-party inspection. Standard purlins typically ship in 20–30 days for full containers.
Ready to specify your purlins? Send us your section drawing (or depth/flange/lip/thickness), coating, and length schedule, and we will confirm formability, coating, and lead time with a fixed-price quote and MTC. Email [email protected] or use the quote form on this page — our team replies within one business day.