All new residential buildings over 18m must now have two staircases. This requirement will reshape UK high-rise architecture, increase costs, and — critically — save lives.. The Single Staircase Problem For decades, the UK permitted residential buildings of unlimited height with a single staircase. This was an outlier internationally — most developed countries have required two staircases in high rise buildings for years. How We Got Here The single staircase approach was predicated on the Stay Put strategy: Only occupants of the affected flat need to evacuate The staircase only needs capacity for one flat's worth of occupants Firefighters use the same staircase for access and rescue Why It Failed at Grenfell When the Stay Put strategy was abandoned at Grenfell Tower, the single staircase was immediately overwhelmed: Residents descending while firefighters were ascending Smoke entering the staircase from compromised lobbies No alternative escape route when the staircase became untenable Wheelchair users with no means of evacuation via stairs "The provision of a single staircase in a residential building of any significant height is an inherent vulnerability that no amount of other fire safety measures can fully compensate for." — Grenfell Tower Inquiry Phase 2 Report The New Requirements Approved Document B — 2025 Amendment From 30 September 2026, all new residential buildings over 18m (approximately 7 storeys) must have: Two protected staircases — both capable of supporting full building evacuation Independent access — each staircase accessible from every floor without passing through the other Fire separation — staircases separated from each other by a full compartment wall Independent ventilation — each staircase must have its own smoke ventilation system Firefighting access — at least one staircase designed as a firefighting shaft Transitional Arrangements Buildings with full plans application submitted before 30 September 2026 — existing rules apply Buildings with initial notice before 30 September 2026 — existing rules apply All other applications after that date — new rules apply Design Implications Floor Plate Efficiency The second staircase has significant implications for building design: Floor plate size Single stair efficiency Dual stair efficiency Loss 400m² 78% 68% 10% 600m² 82% 74% 8% 800m² 85% 78% 7% 1,000m² 87% 81% 6% Smaller floor plates lose proportionally more space, making narrow tower designs less viable. Architectural Approaches Architects are developing creative solutions to accommodate two staircases: Scissor stairs — two interlocking staircases within a single core (used extensively in Asia) Split core — two separate cores at opposite ends of the building Perimeter stairs — external staircases on the building façade Wider buildings — increasing floor plate to absorb the efficiency loss Cost Impact The second staircase adds approximately: 8 12% to construction costs for buildings 18 30m 6 8% for buildings 30 50m 4 6% for buildings over 50m Plus ongoing maintenance costs for additional staircase pressurisation, lighting, and cleaning Fire Engineering Considerations Evacuation Strategy Two staircases enable several improved evacuation approaches: Phased evacuation — fire floor and floor above evacuate first, then floor below, then sequential Simultaneous evacuation — all residents evacuate immediately (practical with two stairs) Defended in place — improved Stay Put with evacuation option always available Smoke Control Each staircase requires independent smoke control: Mechanical pressurisation — maintaining positive pressure to prevent smoke ingress Natural ventilation — openable vents at top and bottom of staircase Hybrid systems — pressurisation with natural relief Firefighting Operations Two staircases transform firefighting operations: Dedicated firefighting staircase — one staircase for fire service access only Resident evacuation staircase — one staircase dedicated to evacuation Separate access points — firefighters and residents don't compete for the same route Existing Single Staircase Buildings The second staircase requirement applies only to new buildings. Existing buildings must rely on: Enhanced compartmentation to support Stay Put Sprinkler retrofit to suppress fires at source Improved fire doors and self closers Enhanced smoke ventilation in the single staircase Evacuation alert systems for when Stay Put is abandoned PEEPs for residents who cannot use stairs Magnus Opifex Second Staircase Services Fire strategy development for dual staircase buildings Evacuation modelling for phased and simultaneous strategies Smoke control design — CFD analysis for staircase pressurisation Code compliance review — ensuring designs meet ADB 2025 requirements Existing building assessments — compensatory measures for single staircase buildings Planning a high rise project? Contact us for expert fire engineering design support.