Doubling Up: Tall buildings and two stairs


Written by Tom Kimber

Tom is an Associate Architectural Technician with BoonBrown offering expertise within the company on building regulations and technical standards.

Email Tom Kimber Find Tom Kimber on LinkedIn

Treading carefully – is the mandating of second staircases in new tall buildings on the horizon?

As part of an ongoing update to elements of Approved Document B, the Department for Levelling Up, Housing and Communities has completed a period of consultation, with the expected conclusions to recommend mandating second staircases in new residential buildings over 30 metres tall.

Such a ‘step change’ in the approach to designing tall buildings will have a significant impact on the plan and layouts, with the stair footprint and interactions requiring accommodating and variation from the established approach; with a single, central stair.

It will affect the internal Net to Gross ratio’s that determine a projects’ viability, including accounting for the area at ground floor, along with the additional emergency egress points to engage with the site and its context. There will likely be implications for the façade treatment and loss of high value perimeter, with potential further effect on other functions within the building, such as services runs, ancillary areas, etc.

Depending on the design, there are times when a second stair can be introduced within the existing stair volume, as an interlocking, or scissor stair. Unfortunately, while this increases escape capacity when appropriate, it is ruled out as a residential solution due to the open void and the need to ensure that the building is easily navigable by both the fire service and residents i.e. at least one staircase must be kept clear of smoke, if the other is overwhelmed.

The implications of the new regulations will require design teams to seek guidance from fire consultants earlier in the project programme, during the initial project work stages, to ensure that layouts are compliant.

Artwork created by Part II Architectural Assistant Daniel Hoang and Office Manager Nadine Richards

Whilst not yet confirmed, it is highly anticipated that any transition period within the building regulations will be very short. Therefore, factoring in a second staircase at the very earliest stages of a project is important to limit the potential impacts on viability, site constraints, specifications and aesthetics.

In fact, since February, the Greater London Authority (GLA) is no longer accepting planning applications for residential towers over 30m, which rely on a single staircase means of escape, irrespective of Building Regulations requirements. The inference is that all new residential towers over 30m should be designed to accommodate two independent stair cores. However, without clear regulatory guidance, compliance is left to interpretation.

Unsurprisingly, we are seeing this hold up developments in London where sites are tight and two stairs are not spatially possible (without compromising viability at least). In anticipation of these changes, some clients with recently approved schemes with a single stair core, are looking to redesign layouts to incorporate a second –concerned that it may not be able to deliver the current scheme.

This move by the GLA reflects the general heightened awareness and concern for safety, for obvious reasons and by acting now, lives may be saved in future, so who can blame them? However, the GLA in acting unilaterally and in advance of the expected revisions to Building Regulations, has also left designers and developers in a quandary. They have also not taken the London Fire Brigade’s advice to implement the two-stair strategy in buildings over 18m – instead making the distinction at 30m.

Space planning and rationalisation of layouts is a key element of design development and at BoonBrown we already adopt a policy of reviewing layouts for optimisation, from the concept design stage, as part of our internal technical audit procedures.

In addition, as required by the ‘Gateways’ for high rise residential developments, introduced in 2021, the inclusion and interaction with specialist fire consultants during the feasibility, concept and planning stages of tall building is ever more important.

As a practice, with studios in London & the South West, we are already taking action in line with the above requirements, regardless of the likely formal rule changes. We will be reviewing all of our tall projects to ensure a robust and viable future.