The most frequent dimensional error — and the one most commonly identified by Building Control on initial inspection — is specifying the overall structural width of the staircase rather than the clear width between the inner faces of the handrails or balustrades. A staircase with a structural width of 1200mm may have a clear width of only 900mm once handrails are accounted for — which is non-compliant under BS 9991.

BS 9991 and Approved Document B require a minimum clear width of 1000mm for fire escape staircases serving residential buildings. For commercial applications, Building Control may specify greater widths depending on occupancy load. Always confirm clear width — not structural width — at the design stage.

This is the most common compliance failure on HMO conversions, apartment projects and commercial refurbishments. Approved Document K distinguishes between three staircase categories — private, common and utility — with significantly different dimensional requirements. Applying private stair dimensions (220mm minimum going, 220mm maximum rise) to a common staircase results in a non-compliant installation.

Common staircases — serving more than one dwelling or used as a means of escape in commercial buildings — require a minimum going of 250mm and a maximum rise of 190mm. Fire escapes under BS 9991 follow the common stair profile. The difference in rise alone (220mm vs 190mm) significantly affects the pitch and structural design of the staircase.

Spiral staircases are frequently specified for fire escape applications because of their compact footprint — but this is a significant design error in most cases. Under BS 9991, spiral staircases are only acceptable as a means of escape where they serve as a secondary escape route and a primary compliant staircase already exists. They are not acceptable as the sole means of escape from upper floors in residential or commercial buildings.

The reason is practical: spiral staircases require users to navigate a continuously changing tread geometry under emergency conditions, significantly slowing evacuation. The tapered treads also make it difficult to achieve the BS 9991 minimum clear width of 1000mm at the walking line while maintaining a structurally practical column diameter.

Landing platforms at each floor level are not optional — they are a structural and regulatory requirement. Common design failures include: platforms that are too shallow (less than 1200mm in depth), platforms that are too narrow (less than the staircase clear width), and platforms where the door swing from the access door reduces the effective clear width below 1000mm when open.

Under Approved Document B and BS 9991, landing platforms must be at least as wide as the staircase and have a minimum clear depth of 1200mm. Where a door opens onto a landing, the door swing must not obstruct the minimum clear width of the escape route — which frequently requires the landing to be larger than the absolute minimum or the door to be recessed.

These are two different requirements and they are regularly confused — with the result that landing balustrades are under-specified. Handrails on the stair pitch must be at 900–1000mm above the pitch line. Balustrades at landing platforms must be a minimum of 1100mm high. Applying the 900mm handrail height to a landing balustrade is a non-compliance failure.

For commercial applications, the balustrade must also resist a horizontal load of 3.0 kN/m under BS 6180 — compared to 0.74 kN/m for residential. A balustrade designed and certified to the residential structural specification cannot be installed in a commercial application. This is frequently overlooked when residential fire escape suppliers quote on commercial projects.

Structural steel is the only appropriate material for external fire escape staircases in the UK. Despite this being well-established in both BS 9991 and Approved Document B, wrong material specifications remain surprisingly common — particularly on residential projects where suppliers with a general construction background rather than fire escape specialism are involved.

Timber is not acceptable for external fire escape staircases under any circumstances. It is combustible, loses structural integrity at temperatures well below those generated by structural fires, and cannot provide the residual load-bearing capacity required by BS 9991 under fire conditions. Aluminium — while corrosion-resistant — loses structural strength rapidly at elevated temperatures and requires specific engineering justification for fire escape applications, which is rarely provided.

All Continox fire escape staircases are fabricated from structural grade S275 or S355 steel to BS EN 10025, hot-dip galvanised to BS EN ISO 1461 or powder-coated over galvanising for external applications. This is the correct specification — full stop.

Since January 2021, all structural steel components placed on the UK market must carry UKCA marking and be accompanied by a Declaration of Performance under the UK Construction Products Regulations. This is a legal requirement — not a quality mark or optional certification. Building Control sign-off on new builds and major refurbishments requires this documentation, and its absence is grounds for rejection of a Building Regulations completion application.

Despite this, a significant number of fire escape staircase suppliers — particularly those operating at the lower end of the market — cannot provide UKCA marking for their structural steel components. This creates a significant compliance gap that frequently only comes to light when a building is being sold, remortgaged or subject to a fire safety inspection.

A fire escape staircase is a structural component that transfers significant loads — dead load, imposed load and dynamic load under emergency evacuation — into the substrate it is fixed to. The fixing substrate (masonry, concrete, steel frame or timber) significantly affects the fixing design, bolt specification and edge distances required. Ignoring the substrate and applying generic fixing details is a structural design failure.

Common substrate-related failures include: anchor bolts specified for concrete being used in aging brickwork without pull-out testing, fixings installed too close to mortar joints or block edges, and base plates welded to fascia rather than fixed into structural elements. Any of these can result in partial or total collapse of the staircase under the dynamic loads generated during an emergency evacuation.

All fire escape staircase installations should include full structural calculations to BS EN 1090 covering both the staircase structure and the fixing design for the specific substrate, produced by a competent structural engineer. See our UK Staircase Building Regulations guide for the full regulatory context.