SFS Technical Data
Section sizes, material properties, structural design standards, and fire performance guidance for Steel Framing Systems (SFS). This page provides the technical basis for specifying SFS infill, loadbearing, and floor systems.
1. Material Specification & Standards
SFS sections are cold-formed from galvanised steel strip. The base material and coating must comply with the following European Standards:
| Property | Standard / Specification | Typical Value / Note |
|---|---|---|
| Base Material | BS EN 10346 | Continuously hot-dip zinc-coated steel strip [citation:1][citation:7] |
| Tolerances | BS EN 10143 | Special tolerances for cold-formed sections [citation:7] |
| Steel Grade | S350GD or S450GD | 350 MPa or 450 MPa yield strength [citation:13] |
| Zinc Coating (Internal) | G275 | 275 g/m² total zinc (both sides). Standard for internal partitions [citation:13] |
| Zinc Coating (External/Coastal) | G350 or C5 | 350 g/m² or C5 coating for corrosive environments [citation:13] |
2. Standard Section Sizes & Gauges
UK standard stud depths are 70mm, 92mm, 100mm, and 150mm at 600mm centres, with bespoke depths available up to 300mm [citation:13]. The gauge (steel thickness) determines structural capacity and fire performance.
| Stud Depth | Common Gauge Range | Typical Application |
|---|---|---|
| 70mm | 0.7mm – 1.2mm | Internal partitions (residential/commercial). Most common UK partition stud [citation:13] |
| 92mm / 90mm | 1.2mm – 1.6mm | Thicker internal partitions (hotel/commercial grade) [citation:13] |
| 100mm | 1.2mm – 2.0mm | External infill walls (low/mid-rise). Standard UK infill depth [citation:13] |
| 150mm | 1.6mm – 2.0mm | External infill (higher thermal targets) or higher-rise buildings [citation:13] |
| 200mm+ | 2.0mm – 3.0mm | Bespoke deep walls for Future Homes thermal targets or specialist loads [citation:13] |
3. Structural Design Considerations
Loads & Deflection
SFS infill walls are designed to support external cladding, insulation, and internal linings against wind load. Design considers dead loads, live loads (loadbearing systems), and wind pressures [citation:2].
Typical Deflection Limits: Vary by cladding type. Blocking and strapping at mid-height is required for studs higher than 3.0m, and third-span blocking for studs over 6.0m [citation:2].
Installation Tolerances
Industry-accepted tolerances for SFS through-wall systems [citation:8]:
- Wall straightness: ±5mm in 3m
- Out of verticality: ±5mm in 3m (H/600 for walls over 3m)
- Structural openings: 10mm wider/deeper than actual window/door to allow for tolerances
4. Fire Performance
SFS fire test data is typically to BS EN 1364-1:2015 (non-loadbearing) or BS EN 1365-1:2012 (loadbearing), tested at UKAS-accredited facilities [citation:3][citation:9].
| System Type | Typical Fire Ratings | Key Note |
|---|---|---|
| SFS Infill (Non-Boundary) | 60, 90, 120 minutes (E) | Integrity only (E) for non-boundary walls [citation:9] |
| SFS Infill (Boundary) | 60, 90, 120 minutes (EI) | Integrity and Insulation (EI) for boundary walls [citation:9] |
| SFS Loadbearing | 60, 90, 120 minutes | Loadbearing test to BS EN 1365-1. Load at test must not be exceeded [citation:2] |
5. Acoustic & Deflection Heads
Acoustic Performance
Approved Document E requires internal walls to achieve 40 dB Rw minimum airborne sound insulation [citation:4]. SFS systems can achieve Rw 45-60+ dB with appropriate board layers, insulation, and twin-frame configurations.
Reducing stud centres can have a detrimental effect on acoustic performance in some systems—always verify the specific build-up [citation:10].
Deflection Heads
Deflection heads accommodate structural movement. Typical allowance is 20mm downward movement [citation:6][citation:12].
Head channels (slotted or deep-leg tracks) must be fixed to the soffit at 600mm centres, with fixings appropriate to the substrate [citation:6].
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