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transfer slabs – recent concerns and what you need to know
Trevor Rushton,
On 19 December 2025, the Building Safety Regulator issued a letter to principal accountable persons and building owners to draw attention to certain risks that have been identified with reinforced concrete multi-storey buildings that include elements of structure known as transfer slabs. The concerns centre upon a lack of clear design methodology for the design of transfer slabs and the propensity for collapse due to punching shear. Whilst no actual collapses are known
to have occurred, the risks have triggered alarm bells in the construction industry, with recent coverage in the CROSS Newsletter (i), guidance from the Institution of Structural Engineers and RICS who have issued a practice alert to surveyors. Building Owners have been advised 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 and/or design (ii).” This information is intended to explain the background to the problem, the role of transfer slabs and the actions that might be required. What is a transfer slab and where might one be found? A transfer slab is simply a thick reinforced concrete floor slab where a column sits on top of a slab but does not have a column immediately below. In other words, it bridges between supporting columns and provides support to columns from the upper parts of a building. Transfer slabs are common in residential and mixed-use commercial buildings, purpose-built student developments and many high-rise structures. Typical uses would include where the column spacing on the ground floor of a building (possibly commercial space) is greater than the spacing on the first floor and above, or where successive
floor plates step back from one another to form terraces. What is the concern? Columns transfer vertical loads to the foundations or other loadbearing elements of a building. The actual load paths can be complex and, in many cases, depend upon the methods used in the design and execution of temporary works when the building is constructed. Furthermore, concrete buildings tend to shrink over time, and this can lead to potentially significant changes in the way that the loads are transferred. Because a transfer slab is taking point loads it must be designed to accommodate the risk of punching shear – the potential for the column to “punch” through the slab in much the same way that a pencil could be pushed through the lid of a cardboard box. Doubts have been expressed over the design methodology
applied to the design of slabs in this scenario. What are the symptoms of punching shear?
One of the difficulties with punching shear is that it is what is termed a brittle failure mode. This means that failures can be sudden, with little or no plastic (permanent) deformation. An early precursor can be the discovery of cracking in the structure, but this cannot be expected to occur in all cases or evidence might be misleading. Indeed, transfer slabs (being thicker than normal) can suffer from significant internal stresses as a result of heat created during curing and longer- term shrinkage – this can also result in the onset of tension cracking particularly where floors and core walls abut. Clearly, evidence of deflection in a flat slab beneath a column might trigger concern, but in an occupied building, particularly
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