Cold-formed galvanized Sigma and Omega profiles for wall cladding girts and ground-mount solar arrays: sectional inertia, wind suction design, and comparison with C/Z purlins.
While roof purlins carry vertical gravity and snow loads, vertical wall cladding is supported by horizontal wall girts resisting intense positive and negative wind pressures. Standard plain C-sections frequently suffer from torsional instability under severe suction. Cold-formed <strong>galvanized Sigma (Σ) profiles</strong>, engineered with distinctive web stiffening channels, deliver 20% to 30% greater sectional inertia and torsional rigidity compared to equal-weight C-sections. For secondary framing and ground-mount solar arrays, symmetrical <strong>Omega (Ω / Top Hat) profiles</strong> provide optimal stability.
1. Wall Girt Mechanics & Wind Action
On 6m to 8m portal column spacing, wall girts bend in the horizontal plane under cyclic aerodynamic wind pressures. To prevent unsightly cladding ripples, deflection must be restricted to L/200. The internal web fold of Sigma profiles provides exceptional resistance against web crippling.
2. Sigma vs. C-Section Performance
At equivalent 2.00mm gauge and depth, a Sigma 200 section withstands 25% higher horizontal wind loads than an unreinforced C-section, enabling broader girt centers and delivering up to 15% net steelwork savings across large facades.
Comprehensive Engineering Comparison Matrix
| Section Geometry | Depth Range | Gauge Range | Torsional Rigidity | Primary Application |
|---|---|---|---|---|
| C-Section | 150 to 250 mm | 1.50 – 2.50 mm | Standard | Simple spans, internal partitions |
| Sigma (Σ) Profile | 150 to 300 mm | 1.50 – 3.00 mm | Superior (Web stiffened) | Heavy wind wall girts, wide spans |
| Omega (Ω) Top Hat | 50 to 120 mm | 1.00 – 2.00 mm | Symmetrical twin flange | Solar racking, cladding sub-frames |
Verdict: Specify overlapped Z-purlins for continuous roof spans, and specify cold-formed Sigma (Σ) girts for wall envelopes to maximize wind resistance and reduce steel tonnage.
Calculate Live with Your Project Dimensions
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Galvanized C / Z / Sigma Purlin Span & Deflection Calculator
Specify your purlin span between trusses, purlin spacing and profile section to calculate deflection limits (L/200, L/300), safe capacity, and required steel tonnage per EN 1993-1-3.
Z200 / 2.00 mm (L = 6.00 m)
Frequently Asked Questions
Should cold-formed galvanized profiles be welded on site? ▼
No. Welding burns the sacrificial zinc barrier, creating immediate rust points. All connections must be pre-punched bolted joints using 8.8 structural bolts.