What you need to know about reinforced concrete transfer slabs

In December 2025, the Building Safety Regulator (BSR) issued a pointed reminder to the UK construction and property sectors: reinforced concrete buildings containing transfer slabs may present greater structural risk than previously understood.

The reminder followed concerns expressed by Collaborating for Safety Structures UK (CROSS-UK) who had issued a commentary on concerns around punching shear in December 2024.

The Institution of Structural Engineers (IStructE) also released guidance in November 2024, which was free to download.

The regulator's notice highlighted uncertainties in historical design practices and the possibility of brittle failure modes – most notably punching shear. Its notice, published on 19 December 2025, urged building owners to 'understand whether they have a transfer slab and seek professional advice where there are visible signs of distress or specific concerns regarding the building's condition.'

The announcement ignited industry-wide attention, and RICS responded in early 2026 with a Practice Alert, advice and FAQs, and a webinar.

Together, these warnings represent a turning point, an acknowledgement that transfer slabs – popular from around 2000 – merit more scrutiny than they have historically received.

The tribunal found that cracking patterns around key support columns and the first‑floor slab indicated a likely punching shear mechanism, severe enough to warrant emergency evacuation and a remediation order under Building Safety Act 2022 (BSA 2022).

This case is significant because it underscores how BSA 2022 is being used to compel landlords to investigate and remedy structural risks, marking an important precedent for managing latent defects in buildings constructed during periods of variable regulatory oversight.

A second case occurred at an East London development, Stratford Halo, where residents of one of the blocks were instructed to leave their homes at four hours' notice after structural investigations raised immediate concerns about the building's stability.

Earlier in the year, ground‑floor tenants in an adjoining part of the development had already been moved to facilitate intrusive checks amid BSA 2022 doubts about the adequacy of key supporting elements.

The situation later escalated when residents of two additional blocks were also evacuated at short notice for structural safety reasons, indicating significant and unresolved concerns about the overall integrity of the estate.

As is to be expected, details of the investigation are currently confidential, and it has not been confirmed that punching shear is the actual mechanism of failure although there is speculation that it is.

Comprehensive national data is limited, but typical buildings include residential developments, student living, hotels – perhaps to a lesser extent – and mixed use.

Many transfer slabs are designed as flat slabs, removing the need for downstand beams and reducing the cost and complexity of temporary works – and it is flat slabs rather than those with downstand beams that harbour concern. But this simplicity masks underlying challenges: to compensate for the absence of beams, these slabs must be significantly thicker.

Greater depth influences thermal behaviour during curing and increases shrinkage, factors that alter their real-world performance. Of course, a slab that is of insufficient thickness or strength could suffer from excessive deflection and this could create its own set of fabric and user problems.

Because punching shear failures offer little warning, even small inaccuracies in structural reinforcement modelling or construction can have significant consequences.

There have been some notable examples of this form of failure – the Pipers Row car park case in 1997 being regularly cited – although the circumstances here did not relate to transfer slabs but to a form of construction known as lift slab where floors are cast at ground level and then jacked up into position.

In this case poor repairs, a lack of efficient connections between floor slabs and general neglect were major triggers – punching shear was the end result of a number of contributory factors.

Similarly, the central issue in the 2021 collapse of the Champlain Towers residential block in Florida was the insufficient punching‑shear capacity of the pool‑deck slab, whose design did not adequately account for the applied loads.

Additional landscaping features significantly increased these stresses, and it remains uncertain whether the original design considered the topping slab or the added planters.

Recent analysis by IStructE suggests that some earlier structural modelling codes and guidance practices did not adequately account for:

• the complex interaction between offset columns above and below a slab
• the structural effects of temporary works during construction
• the long-term shrinkage behaviour of thick slabs.

These factors can result in higher in‑service shear forces and axial loads than originally anticipated. Signs of distress can be difficult to interpret; early warning may take the form of excessive deflection of floor slabs or unusual cracking to floor slabs and columns, but in many cases completed finishes may conceal the evidence.

Cracking that a surveyor may previously have dismissed as the effects of normal shrinkage may be more significant, particularly if it exists in the vicinity of column heads.

Before November 2024, when IStructE published its Design of transfer slabs guidance, there was no universally accepted methodology. The transition from prescriptive British Standards to the more principles‑based Eurocodes BS EN 1990–1999 in 2005 gave engineers more discretion, but also introduced notable variations in approach.

With increasingly sophisticated 3D modelling software and finite element analysis being adopted across the industry, the absence of standardised assumptions meant that actual in-service loads and stresses could be materially underestimated.

The IStructE guidance on punching shear and transfer slabs, published in December 2025, aimed to rectify this, establishing clearer methodologies for both new design and assessment of existing structures.

Note that a failure to comply with the latest guidance does not necessarily mean that a transfer slab is defective, but it does trigger a need for reassurance.

A reasonable initial review typically begins with a drawing-based desktop study. Differences in column grids or unusually thick floor slabs can indicate a transfer structure. Where possible, physical inspection of exposed soffits may help confirm slab depth and configuration. However, architectural finishes, insulation, raised floors and mechanical installations often obscure structural elements, limiting visibility.

Surveyors may also encounter cracks, localised deflection, or out‑of‑plumb columns, but these require cautious interpretation.

Non‑destructive testing can help estimate depth and sometimes reinforcement layout, but verifying the presence and spacing of 'as-built' shear reinforcement remains difficult.

Furthermore, temporary works used during the original construction can significantly influence early-age behaviour and load distribution, yet records of these systems are often unavailable. In some cases, the outcome may remain inconclusive, and periodic monitoring – ranging from visual inspections to sensor-based deflection tracking – may offer the most pragmatic mitigation strategy.

Initial measures could include:

• identifying whether a transfer slab exists
• gathering available design and construction documentation
• being aware that crack patterns could be significant; look out for signs of deflection – this may be hard to identify but effects on floor levels, furniture, window and door fit, partitions and the like could be indicators
• escalating to a chartered structural engineer who is familiar with and fully competent in the issues whenever uncertainty arises
• for HRBs, ensuring that any findings inform the building safety case.

As further guidance emerges, the industry's task is to approach the issue with balance: acknowledging the genuine concerns while avoiding unnecessary alarm. Transfer slabs have performed successfully in many buildings, but they demand respect, and in some cases, renewed scrutiny.