When Prescriptive Codes Are Not Enough

Approved Document B and the relevant British Standards work well for conventional building types. For buildings with unusual geometry, complex occupancy arrangements, or innovative design, the prescriptive guidance runs out — and performance-based fire engineering is required to demonstrate that the building achieves an acceptable level of fire safety.

Understanding the specific fire safety challenges of complex buildings — and how fire engineers address them — is important for architects and developers working with these building types.

Atria and Voids

Buildings with large atria or internal voids present a fundamental fire engineering challenge: the atrium creates a direct connection between multiple floor levels, enabling fire and smoke to spread vertically without the protection of floor-by-floor compartmentation. The fire strategy must address smoke control in the atrium — typically through engineered smoke extract systems designed to keep the atrium clear of smoke for sufficient time to allow evacuation — and means of escape routes that do not require occupants to pass through the potentially smoke-filled atrium.

Underground Spaces

Underground car parks, basement retail, and below-ground plant rooms present fire safety challenges driven by the difficulty of firefighting access, the absence of natural ventilation, and the length of escape routes to the surface. Approved Document B does not provide comprehensive guidance for underground spaces — performance-based fire engineering is typically required to design smoke control, suppression and means of escape systems for complex basement developments.

Tall Buildings

High-rise buildings — particularly those above 50 metres — present fire safety challenges that go well beyond the ADB guidance for buildings over 18 metres. Stack effect (the pressure differential between inside and outside caused by the height of the building) can drive smoke into stairwells and escape routes. Evacuation management for very large populations is complex. Firefighting at height requires specialised strategies. Performance-based fire engineering is typically required for the tallest buildings.

Mixed Occupancy Interfaces

Where a single building contains fundamentally different occupancy types — residential above retail, office above hotel, leisure within a residential development — the interface between occupancies creates fire engineering complexity. Different evacuation strategies, different alarm systems, different compartmentation standards, and different management arrangements all need to be addressed coherently in a single fire strategy.

Heritage and Listed Buildings

Historic buildings present unique constraints: fire safety interventions must preserve historic fabric, modern systems may be intrusive or impossible to install, and the building's existing configuration — often developed without fire safety in mind — may create significant challenges for means of escape and compartmentation. Performance-based fire engineering, typically combining enhanced detection, suppression and management measures, is almost always required for significant works to listed or heritage buildings.