Published 6 October 2026
What each system actually is
SFS is a lightweight wall made from cold rolled galvanised steel studs and tracks, usually 100mm to 150mm deep for infill work and set at 600mm centres or closer. It is fixed between the floors of a steel or concrete frame, then faced with a sheathing board on the outside and plasterboard on the inside, with insulation in and over the studs.
Blockwork is the familiar option: dense or lightweight concrete blocks laid in mortar, normally as the inner leaf of a cavity wall or as infill to a frame. Bricklayers build it course by course, and it needs time to cure before it can take load or finishes.
Speed, weight and weather
Speed is where SFS usually wins. A team of fixers can often close in a floor of a mid sized building in days rather than weeks, and once the sheathing board is on and taped, the internal trades can start while the outside cladding follows. That matters on a Sheffield programme running through autumn and winter, because mortar should not be laid when the temperature drops to around 3°C and falling, and exposed sites up towards Crookes, Stannington or the Peak fringe lose more days to frost and rain than sites in the valley bottoms.
Weight is the other big difference. An SFS wall with boards and insulation typically comes in at roughly 40 to 60kg per square metre, while a blockwork inner leaf is often 150 to 250kg per square metre depending on the block. That lighter load can mean smaller foundations and a lighter frame, which is especially useful for rooftop extensions on older buildings and on sloping or made ground, both common around the city.
- SFS: fast, dry, light, less affected by cold weather, needs accurate design and setting out
- Blockwork: slower and wet, heavy, robust, materials and skills easy to source locally
- SFS suits framed buildings of several storeys; blockwork suits houses and low rise load bearing work
Fire, sound and thermal performance
Blockwork is non combustible and gives good fire resistance and sound insulation through sheer mass, with very little to go wrong. A 100mm dense block wall will comfortably achieve 60 minutes or more in most arrangements.
SFS can match it, commonly 60, 90 or 120 minutes, but only as a tested system. The performance comes from the exact combination of stud, board type, number of board layers, insulation and fixings that the manufacturer has tested. Swap one board for a cheaper one, or miss the fire stopping at the slab edge and around openings, and the rating on paper no longer applies. This is the detail that most often gets missed, and it is worth asking who is responsible for it and how it will be recorded.
On thermal performance, SFS walls can reach low U values in a slimmer build up, but steel conducts heat, so most of the insulation needs to sit outside the studs to avoid cold bridging and condensation.
What it costs and which to choose
On materials and labour alone, blockwork is often the cheaper wall per square metre, and for a single house extension in Sheffield it is usually the sensible choice. The supply chain is local, builders know it, and the scaffold is going up anyway.
SFS tends to cost more per square metre for the wall itself, but the comparison shifts on larger jobs once you count a shorter programme, reduced site running costs, lighter foundations and earlier access for internal trades. As a rough guide, the bigger and taller the building and the tighter the site, the stronger the case for SFS. City centre plots with little storage space and restricted deliveries also favour it, since steel sections arrive bundled and take up far less room than pallets of blocks.
The decision depends on the height of the building, the structural frame, ground conditions, the time of year and what the engineer and Building Control will accept. Get the structural engineer and the installer talking early, because changing system after the frame is designed is expensive.
