Introduction: The Secondary Skeleton
Primary frames hold the building. Purlins and girts hold the roof and walls. Specify cheap secondary framing, and high winds will tear the roof panels off completely. As a specialized steel building secondary framing supplier, I see overseas buyers guessing between C and Z profiles constantly. It is not a random choice. Structural mechanics dictate the profile. Here at Propanel, I am Feng. We source and supply the absolute best. This is the engineering truth behind cold-formed steel framing.
1. Material and Galvanization Standards
Mild steel is dead weight here. You need absolute strength to bridge wide spans.
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Steel Grade: Specify high tensile structural steel exclusively. G345 (fy ≥ 345 MPa) or G450 (fy ≥ 450 MPa). It resists bending and deflection under heavy wind uplift.
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Corrosion Coating: Roof leaks destroy ungalvanized purlins. Z275 hot-dip galvanization is mandatory (275 g/m² total both sides, ≥ 20 μm zinc per face). White rust halts immediately.
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CNC Punching Modulus: Do not drill holes on-site. Field drilling destroys the zinc coating and creates rust points. Our partner OEM factories utilize this exact CNC modulus: (L – 70mm) / 75mm = Positive Integer N. Millimeter-perfect bolt hole alignment. Zero field modifications.
2. Z-Section Profiles (The Nesting Kings)
Look closely at a Z purlin. The flanges are asymmetric. Top flange (W1) is 70mm. Bottom flange (W2) is 63mm. Why? Because they must nest (overlap) over the primary rigid frame. Overlapping transforms simple spans into a continuous beam system. Bending capacity spikes massively. Deflection drops. As a professional B2B supplier, we mandate Z profiles for heavy-load multi-span roofs.
| Section Type |
Web Depth (H) |
Top Flange (W1) |
Btm Flange (W2) |
Lip (D) |
Thickness (mm) |
Weight (kg/m) |
Standard Part No. |
| Z165 | 165 mm | 70 mm | 63 mm | 20 mm | 1.5 ~ 2.5 | 4.06 ~ 6.71 | G903055 ~ G810114 |
| Z200 | 200 mm | 75 mm | 68 mm | 20 mm | 1.5 ~ 3.0 | 4.47 ~ 8.83 | G810110 ~ G810495 |
| Z240 | 240 mm | 75 mm | 68 mm | 20 mm | 1.5 ~ 3.0 | 4.94 ~ 9.77 | G810108 ~ G810124 |
| Z292 | 292 mm | 90 mm | 82 mm | 25 mm | 1.5 ~ 3.0 | 5.59 ~ 11.00 | G810850 ~ G810775 |
3. C-Section Profiles (Simple Spans)
A cold formed C section steel girt has symmetric flanges. 75mm top and 75mm bottom. They cannot overlap. They butt end-to-end. We supply them strictly for simple simply-supported spans. Wall girts. Window and door framing jambs. The geometry makes bolted bracket connections straightforward.
| Section Type |
Web Depth (H) |
Btm Flange (W2) |
Lip (D) |
Thickness (mm) |
Weight (kg/m) |
Standard Part No. |
| C165 | 165 mm | 65 mm | 20 mm | 1.5 ~ 3.0 | 3.71 ~ 7.15 | G100082 ~ G810326 |
| C200 | 200 mm | 75 mm | 20 mm | 1.5 ~ 3.0 | 4.58 ~ 8.94 | G810798 ~ G810801 |
| C240 | 240 mm | 75 mm | 20 mm | 1.5 ~ 3.0 | 5.07 ~ 9.89 | G810402 ~ G810406 |
| C250 | 250 mm | 75 mm | 20 mm | 1.5 ~ 3.0 | 5.07 ~ 9.89 | G100092 ~ G810409 |
| C292 | 292 mm | 90 mm | 25 mm | 1.5 ~ 3.0 | 6.15 ~ 12.16 | G100086 ~ G100084 |