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SFS studs come in a range of widths — from 70mm up to 300mm and beyond. Each width has a purpose. Picking the wrong one wastes money or fails to meet the performance the project requires. This guide explains what every common SFS stud size is actually for, what it can span, and how to choose the right one.

What is an SFS stud?

An SFS stud is a cold-rolled steel C-section (sometimes called a C stud, or an I stud when the profile is I-shaped). It forms the vertical framing in a Steel Framing System wall. Studs sit inside a base track at the floor and a head track at the ceiling, and are spaced at centres — typically 600mm for standard applications, sometimes 400mm or 300mm where the loads are higher.

The two dimensions that matter on a stud are:

• Width — the depth of the C section, measured across the flanges. This determines how tall the wall can be, how much acoustic insulation fits, and how much the frame costs.
• Gauge — the thickness of the steel (1.2mm, 1.5mm or 2.0mm typically). This determines strength and stiffness at a given width.

Width and gauge work together. A 70mm × 2.0mm stud is stronger than a 70mm × 1.2mm stud, but a 90mm × 1.2mm stud may still be stronger than the 70mm × 2.0mm in some load cases. When specifying, always check the manufacturer's span table for the exact width/gauge combination against your wall height and wind loading.

SFS stud sizes — the full table

The following are the standard SFS stud widths stocked by National Drylining and most UK suppliers. The "typical application" column is a starting point, not a rule — actual selection depends on height, loading, fire, acoustic, and other factors.

Which size for which application?

As a starting point:

Domestic partitions (inside a house)

48mm or 50mm studs are almost always sufficient. Domestic partitions rarely exceed 2.7m in height, have no wind loading, and only carry plasterboard. Choose 70mm if the partition needs to be acoustic (e.g. between bedrooms) or fire-rated (e.g. between a garage and a habitable room).

Commercial partitions (offices, schools, hospitals)

70mm or 90mm are the standard. Larger widths give better acoustic performance, allow for service voids, and are compatible with the fire ratings that commercial projects need.

SFS infill walls (external building envelopes)

70mm is the minimum. 90mm or 100mm is more common, especially on mid-rise buildings. For buildings over 10m, or in exposed wind conditions, 120mm, 150mm or larger may be required.

Loadbearing SFS walls

100mm minimum. Most loadbearing applications use 150mm, 200mm or larger. The size is determined by structural engineering — the wall carries loads from above and must be sized for those loads, not just wind and fire.

High acoustic performance

Wider studs allow thicker insulation and better acoustic separation. For a Rw 55+ wall, 90mm or 100mm is standard. For Rw 60+, 120mm or twin-frame construction with 90mm studs each side is used.

Stud size by wall height

Wall height is one of the biggest factors in stud selection. A rough guide:

Stud size for acoustic performance

Acoustic separation depends on mass (board layers), isolation (resilient bars or twin frames), and the depth of the cavity. A wider stud increases the cavity depth, which allows more insulation and better acoustic performance.

Rough acoustic performance by stud size (single-frame, standard build-up, 2 × 12.5mm board each side, insulation in cavity):

• 70mm stud — Rw 40–45 (basic acoustic)
• 90mm stud — Rw 45–50
• 100mm stud — Rw 48–52
• 120mm stud — Rw 50–55
• 150mm stud — Rw 53–58
• Twin-frame 70mm each side — Rw 58–62
• Twin-frame 90mm each side — Rw 60–65

Note: these are Rw (laboratory) figures. On-site R'w will typically be 3–8 dB lower depending on flanking transmission and workmanship.

Stud size for fire rating

Fire rating is primarily determined by the board layers, not the stud width. However:

• 30-minute — any stud size, single layer of fire-rated board each side
• 60-minute — 70mm+ stud, single or double layer depending on the tested build-up
• 90-minute — 70mm+ stud, double layer usually required
• 120-minute — 90mm+ stud, double or triple layer depending on the tested system

See our full Fire-Rated Partitions guide and Fire Tested Build-Ups register for tested constructions.

When to oversize (and when not to)

Oversize (use the next size up from the minimum) when:

• The wall will carry heavy items (TVs, radiators, shelving)
• The wall is on a high floor of a building (wind load increases with height)
• The wall is in an exposed wind location (coastal, open terrain, high rise)
• The wall needs high acoustic performance (music rooms, hotels, hospitals)
• The wall is part of a structural system where deflection matters

Don't oversize when:

• The wall is a simple internal partition in a domestic setting
• The acoustic performance is already achieved by the board and insulation
• Cost and wall thickness are a concern (larger studs = thicker walls = less floor space)
• The build-up needs to fit within a tight service void

Summary

SFS stud size is not a one-size-fits-all decision. The right size depends on wall height, load, acoustic performance, fire rating, exposure, and available space. As a starting point:

• Domestic partitions: 48mm, 50mm, or 70mm
• Commercial partitions: 70mm or 90mm
• SFS infill: 70mm minimum, 90mm or 100mm standard
• Loadbearing: 100mm minimum, engineer to specify
• High acoustic: 90mm or larger, or twin-frame
• High rise: 120mm – 300mm, structural engineering required

For any project where the wall height exceeds 4m, wind loading is significant, or the acoustic or fire performance is critical, always confirm the selection with a qualified structural engineer or by checking the manufacturer's span tables against the specific project conditions.