SFS Framing in the City of London: What It Is and When to Use It

What SFS framing actually is

SFS stands for steel framing system. It is a wall structure made from cold-rolled galvanised steel studs and tracks, fixed together on site to form the external walls of a building. Once the frame is up, it is covered with a sheathing board on the outside, filled with insulation and lined with plasterboard on the inside. The cladding, brick slips or render then fix to the outer face.

It looks like the metal stud partitions used inside offices and flats, but it is a much heavier product. Internal partition studs are typically 0.5 to 0.9 mm thick. SFS sections are usually 1.2 to 2.0 mm thick and 100 to 300 mm deep, because they have to resist wind load and carry the cladding. Every SFS wall should be designed by a structural engineer, not sized by eye.

The three types you will come across

Which type you need depends on the building's main structure.

• Infill: studs sit between the floor slabs of a concrete or steel frame. This is the most common arrangement on City office and residential blocks.
• Oversail: studs run past the slab edge on brackets, leaving room for continuous insulation and suiting taller floor heights.
• Load-bearing: the steel frame carries the floors and roof itself. It is used on low to medium rise buildings and rooftop extensions.

When it suits a City of London project

Sites in the Square Mile are tight, with little storage and restricted deliveries. SFS arrives in bundles, often pre-cut to length, and can be carried by hand or lifted on a hoist. There is no mortar, no mixing and far less mess than blockwork. A finished SFS wall also weighs a fraction of a masonry one, which matters when the existing structure has limited spare capacity.

It is not always the right answer. For a short stretch of wall at ground level, or a very small job, blockwork can be simpler and the cost of engineering design may outweigh the benefit.

• Rooftop extensions and extra storeys on existing buildings
• Replacing an outdated facade on a retained frame
• New build infill walls on concrete or steel frames
• Sites where handling blocks and wet materials is impractical

Fire safety, approvals and site rules

On residential buildings over 18 m, the materials in the external wall must be non-combustible, meaning class A1 or A2-s1,d0. Steel passes easily, but the sheathing board, insulation and cavity barriers have to comply too. Buildings of 18 m or seven storeys with at least two homes are classed as higher-risk, and need Building Safety Regulator approval before work starts. That can add several months, so raise it early.

The City of London Corporation is the planning authority, and much of the area sits in conservation areas or involves listed buildings, so changes to the outside usually need consent. The Corporation's code of practice for construction sites also restricts noisy work, typically with quiet periods mid-morning and mid-afternoon on weekdays. Cutting steel counts as noisy, which is another reason pre-cut sections help. Check the current code for your site, and expect deliveries to need booked slots.

What it costs and how long it takes

As a rough guide, expect £70 to £130 per square metre of wall for the framing and sheathing board on a City job, before insulation, cladding and internal linings. The figure depends on stud depth and gauge, floor heights, the number of window openings, hoisting and access, and the working hours allowed. City projects tend to sit towards the upper end because of logistics.

Allow two to four weeks for engineering design and drawings, plus two to three weeks for manufacture if the sections are pre-cut. On site, a typical floor of infill framing goes up in days, not weeks. A reliable quote needs drawings and a site visit, not a rate per metre over the phone.