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 not exceed that of any other structural element when properly designed. 

However, in recent years, several examples of design issues have emerged, influencing how engineers assess the likelihood of failure. The December 2025 decision by the First tier Tribunal in the Wotton Court, London, is one example in which 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 a gap in existing standards and guidance for engineers on this issue.

This technical guidance is therefore thorough, insightful, and focused on filling the 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?

At Cundall, we have delivered over 100 structural risk assessments of higher-risk buildings (HRBs) 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, and 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 expectancy
• 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 a 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 designs that have required prompt mitigation measures. However, if a competent structural engineer has assessed the situation and undertaken a proportionate evidence-led 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 will need to put slightly stronger but still reasonable monitoring in place. This is in line with good practice anyway, because high‑rise buildings must keep their Building Assessment Certificate up to date and renew it every five years.

¹ What is a transfer slab – When the structural columns in a building are not continuous from the roof to the foundation level, a transfer element is required to transfer the applied vertical loads from the upper section of the column into the lower section. A common scenario in buildings is where the structural column spacing on residential floors differs from that in an area of lower-level car parking. When a slab element is used to transfer these vertical forces horizontally (as opposed to a beam) is it referred to as a “transfer slab”.

²A Building Remediation Order is a legal order that instructs a building owner that they must fix specific safety defects by a deadline determined by a tribunal. It’s an instrument created under the Building Safety Act to make sure important fire‑safety or structural-safety problems are addressed.

³ Proportionality should be maintained throughout the exercise, and intrusive investigation is not a default, but it should be evidence-based on the above points and draw upon the wider knowledge of a competent structural engineer.