Structural engineering comparison between 27/200 and 38/151 trapezoidal sheet profiles regarding rib depth, moment of inertia, purlin spans, and sheet thicknesses.
For uninsulated single-skin envelopes, canopy roofs, and site-assembled double-skin wall systems, specifying the correct profile geometry (27/200 vs. 38/151) and steel substrate thickness (0.50 mm to 1.00 mm) dictates structural span capability. Because bending stiffness is proportional to the cube of profile depth, millimeters of rib height translate into significant purlin span extensions.
1. Rib Depth, Moment of Inertia, and Bending Stiffness
Profiled sheet structural performance is governed by rib height and cross-sectional geometry. With its 38 mm rib depth, profile 38/151 delivers an approximately 80% increase in moment of inertia (Ix) compared to standard 27 mm profiles, resisting deflection under heavy snow and wind pressure loads.
2. Profile 27/200: Maximum Cover Width (1000 mm) and Economy
Roll-formed from standard 1250 mm coils, 27/200 yields exactly 1,000 mm effective cover width across 5 trapezoidal ribs. This 1-meter module simplifies site take-offs, reduces side-lap joint wastage, and represents the most cost-effective cladding profile for purlin spans up to 1.50 meters.
3. Profile 38/151: Deep Ribs, Extended Purlin Spans, and Snow Loads
Profile 38/151 provides a net cover width of 910 mm with deep 38 mm trapezoids spaced at 151 mm pitch. Designed for heavy structural duties, it spans 1.80 to 2.50 meters between purlins, making it mandatory for high snow load regions and pre-engineered metal buildings with wide bay spacing.
4. Substrate Thickness (0.50 mm to 1.00 mm) & Deflection Limits (L/200)
In compliance with EN 14782, maximum allowable live load deflection is limited to L/200. While 0.50 mm serves as the minimum safe walkability gauge for roofs, industrial facilities with 2.0 m+ purlin spans should specify 0.60 mm or 0.70 mm structural steel.
Comprehensive Engineering Comparison Matrix
| Technical Parameter | 27/200 Profiled Sheet | 38/151 Profiled Sheet |
|---|---|---|
| Rib Depth (Height) | 27 mm | 38 mm (+40% deeper section) |
| Effective Cover Width | 1,000 mm (1.00 m module) | 910 mm (0.91 m module) |
| Max Recommended Purlin Span | 1.20 – 1.50 meters | 1.80 – 2.50 meters |
| Moment of Inertia (Ix) | Standard stiffness | High stiffness (~80% higher capacity) |
| Snow Load Suitability | Low to moderate snow zones | Heavy snow zones (Alpine / Continental) |
| Primary Applications | Wall cladding, standard canopies, sheds | Heavy industrial roofs, wide purlin bays |
| Available Gauges | 0.50 mm – 0.70 mm | 0.50 mm – 1.00 mm |
Specify 27/200 for wall cladding and standard 1.20 m purlin roofs for maximum economic cover; specify 38/151 for roofs requiring purlin spans up to 2.50 m under heavy snow loads.
Calculate Live with Your Project Dimensions
Apply the engineering criteria from this guide to your specific building; estimate take-offs, load capacities, and logistics instantly.
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
What is the minimum recommended gauge for roof sheets? ▼
For walkable roofs under maintenance loads, 0.50 mm is the absolute minimum standard; 0.40 mm sheets are restricted to temporary site hoarding and vertical fencing.
Why is cover width narrower on 38/151 than 27/200? ▼
Because forming deeper 38 mm ribs draws more strip metal from the initial 1250 mm master coil, yielding 910 mm net cover vs 1000 mm on shallower 27 mm profiles.