My building has a transfer slab should I be worried……?

In December 2025, correspondence from the Building Safety Regulator (BSR) to building owners and those responsible for the safe operation of buildings, raised the profile of the humble transfer slab ¹ across England. From an engineering perspective, the BSR content strikes a reasoned balance between awareness and concern. While transfer slabs have a higher consequence of failure, their likelihood of failure should be no greater than any other structural element when properly designed. 

However, in recent years several examples of design issues have emerged, influencing how engineers assess their likelihood of failure. The December 2025 decision by the First tier Tribunal in the Wooton Court, London, is one example where transfer slab issues resulted in a Building Remediation Order².

In late 2024, the Institution of Structural Engineers and the Concrete Centre issued guidance clarifying design best practice. This included an early‑stage conceptual design sizing guide and outlined common errors in design approaches. They noted that there was a gap in existing standards and guidance for engineers on this issue.

This technical guidance is therefore thorough, insightful, and focused on filling a clear gap in industry‑wide content on the topic. However, it is written primarily for structural engineers and is consequently less useful as an educational tool for a broader audience. 

How does this apply to practice?

Cundall has delivered over 100 structural risk assessments of higher-risk buildings (HRB’s) in the period since the Building Assessment Certification (BAC) regime was created and the need for professional structural input into the process was then clarified by the BSR. These buildings are securing BAC approvals with reassuring regularity, consequently building occupants are being served well by the wider process.

During the course of this work, Cundall has assessed the risk of many transfer slabs of different ages and in various configurations. Elements of this type are a key interest to the BSR and form a specific hazard to building occupants that requires consideration. This structural assessment of the risk needs to consider: 

• Slab depth
• Column spacing and general configuration
• Applied loads present (design and actual)
• Exposure to external elements that have the potential to reduce life
• Wider provision for disproportionate collapse in the as-constructed structural frame³

To feed into this, the sources of evidence are similar to general BAC focused structural risk assessments:

• Evidence of original design details / approach
• Visual evidence from the as-constructed elements which have been subject to applied loading over a long period of time  

Reassuringly, the vast majority we have assessed and then communicated to the BSR have not merited anything over and above a defined life-cycle risk management regime that aligns with similarly significant structural elements.

In summary, the presence of transfer slab should not be unduly concerning for building operators or the occupants. It does require assessment by a competent engineer and there are examples of historic erroneous design that have required prompt mitigation measures. However, if a competent structural engineer has assessed the situation and undertaken a proportionate evidence lead risk assessment (and for an HRB engaged with the BSR through the BAC process), there is no inherent reason why occupants will be exposed to any excessive ongoing risk. It is likely that the building operator may need an enhanced yet proportionate monitoring regime but this aligns with good practice that, for HRB’s, the ongoing BAC approval and 5 year cycle of renewal demands anyway.