Each month, PTE's Knowledge Hub team will explore the complexities and technical challenges British project architects face every day. First up, fire safety.

As far as British Standards go, expectations for this one were riding high ahead of its publication. That’s because the newly minted BS 9991 Fire Safety in Residential Buildings aims to resolve discrepancies between Approved Document Part B, government guidance, and expert commentary. In this regard, some progress has been made but contradictions remain, making full compliance and practical design integration challenging. These are key issues – and our view on them – that matter most.

Ground Floor Exits
The requirement for imperforate separation between exits from multiple stairs ensures a clear escape route but complicates design. When both stairs serve everyday use, residents may need to re-enter the building after exiting just to access amenities like mail collection. Although this requirement has appeared in previous guidance, it could create a peculiar arrangement when the stairs are adjacent - the most common arrangement.

Lift Lobbies
Best practice suggests users should board the first available lift, as seen in commercial buildings. However, BS 9991 mandates separate lobbies for different lift banks, limiting movement and reducing efficiency.

Corridor Services
Corridors distribute substantial services, often leading to conflict between fire safety and electrical engineering standards. While routing services through lobbies is now permitted, ensuring both fire protection and accessibility remains a challenge.

Stair Width and Dimensions
BS 9991 now references BS 5395:2010, increasing minimum tread depth from 250mm to 300mm - adding 550mm to a straight flight or 300mm to a dogleg stair. This raises concerns about whether compliance with Part K remains acceptable or would now be seen as an inferior standard.

Design & Regulatory Impact
The revised guidance significantly affects communal space planning and street-to-home movement. The lack of diagrams complicates interpretation, requiring careful architectural input. Unlike Approved Documents, BS standards take immediate effect. While Build UK initially suggested older BS-based designs would be accepted by the Building Safety Regulator (BSR), this no longer appears to be the case for projects moving into Gateway 1.

In a Nutshell
BS 9991 introduces logical updates but does not fully resolve regulatory or practical conflicts. The risk remains that buildings will be designed for compliance only, rather than functionality. Until further revisions, architects must navigate ambiguities while ensuring holistic regulatory compliance.