Transfer Slabs – Recent Concerns and what you need to know
Trevor Rushton
On 19th 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.
The risks were first mooted in November 2024 with the publication of IStructE Guidance on transfer slabs and in the CROSS Newsletter(i) published in December of that year. RICS have subsequently issued a practice alert to surveyors. To our knowledge, at least two cases of emergency evacuation of buildings have occurred and 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 brief information paper 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?
Figure 1 Sketch showing potential transfer slab locations.
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 developments, student accommodation, hotels and mixed-use commercial buildings of between 5 and 20 storeys. 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.
Transfer slabs have become popular since around 2000, but at present there is no data to confirm how many buildings contain them.
Typically, transfer slabs are flat slabs; they do not have downstand beams which makes the construction of temporary formwork easier and cheaper to build. However, slabs are much thicker than normal floors (as a rule of thumb 75mm thickness per storey height) and this can have repercussions in terms of temporary support, the need for large volume continuous pours and the effects of heat and drying shrinkage following placement.
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 was 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. Engineers have found that the shear (slicing) forces (and live loads) encountered can be much higher than originally envisaged, particularly where there are short distances between offset columns.
Figure 2 Drawing showing cracking patterns in a floor slab arising from punching shear. Such cracking would occur at failure and may not be apparent prior to this.
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 with suspended ceiling finishes, it might be very difficult to identify such movement without very detailed measurement.
Are there any reports of failures in Transfer slabs?
So far as is known there have not been any physical collapses due to the failure of transfer slabs, but there are several potentially high-profile cases involving the rapid evacuation of buildings.
A recent First-tier Tribunal decision has ordered remediation works in a case concerning structural risks linked to punching shear at Wotton Court, a 12‑storey residential building. Investigations identified cracking around key load‑bearing columns and the first‑floor slab that was consistent with a punching‑shear type failure. The tribunal judged the risk sufficiently serious to justify the emergency evacuation of residents and the issuing of a remediation order under the Building Safety Act 2022 (BSA 2022).
This ruling is important because it demonstrates how the BSA 2022 is now being used to require landlords to thoroughly investigate and rectify structural safety issues, particularly where buildings may contain latent defects arising from periods of inconsistent regulatory oversight.
A similar situation is reported to have unfolded at the Stratford Halo development in East London. Residents in one of the blocks were instructed to vacate their homes at only four hours’ notice after structural investigations raised urgent concerns about the building’s stability. Earlier in the year, ground‑floor commercial tenants in an adjacent building had already been relocated to allow intrusive checks after questions were raised—again under the BSA 2022 framework—about the adequacy of critical supporting elements.
The situation subsequently escalated when two further blocks on the estate were also evacuated at short notice due to unresolved structural safety issues. While the detailed findings of the ongoing investigations remain confidential, there is widespread speculation that punching‑shear‑related weaknesses may be implicated, although this has not been formally confirmed.
Are transfer slabs designed using established principles?
Not until recently; until IStructE published its recommendations in November 2024 various design and modelling methods were used with no universally accepted methodology. Whereas at one time British Standards were issued as codes of practice, their replacements, in 2005, by the Structural Eurocodes (BS EN1990-1999) are more performance based (setting verification limits) and less informative. Whilst BS 8110 has been withdrawn, compliance with Building Regulations is not dependent upon a specific code as long as the functional requirements are met (iii). Thus, there is scope for various design methodologies including software-based techniques such as finite element analysis and 3d modelling; this is all well and good, but the uncertainty lies in the lack of consistency, the complexity of the different forces at play and the risk that a “one size fits all” approach to design can fail to provide adequate capacity.
So, what has been done to address the problem?
The Institution of Structural Engineers has published guidance on this issue, see Design of Transfer Slabs in November 2024 (iv). The guidance can be downloaded freely from the Institution’s website. Although primarily intended for engineers to establish standard methodologies in design, the guide also provides advice in the verification of existing structures; something that ultimately will require engineering input.
What has RICS recommended?
In its Practice Alert of 14th January 2026 (v), RICS draws mainly upon the Building Safey Regulators advice of 19th December: “The government is currently recommending that where there are visible signs of distress or specific concerns regarding a building’s condition or design, building owners should seek immediate professional advice. RICS members who are chartered building surveyors may be instructed to carry out condition surveys of such tall buildings to identify buildings with transfer slabs. If a building is identified, then a suitable expert structural engineer will be required to carry out more in-depth analysis. RICS recommends that IStructE are contacted for suitable competent engineers.”
Is there reason to be concerned?
Yes and no. Clearly the risks are such that a warning should be issued, but the mere existence of a transfer slab does not mean that failure is inevitable or that immediate steps need be taken to evacuate the building or to provide additional precautions against collapse. The BSR is currently working with the Building Advisory Committee in co-operation with MHCLG and so further guidance is likely to be issued in due course.
However, a prudent first step would be to review any potential cases to see if a transfer slab is likely to exist and thus start to narrow the issue down to more manageable proportions. Such an exercise ought to be within the remit of suitably experienced Chartered Building Surveyors in the first instance but detailed analysis is something that will demand structural engineering advice. A desktop study of construction drawings ought to indicate whether there is potential for a transfer slab, but this will probably need to be followed up by site inspection. Examination of the structural philosophy (if it is within the health and safety file) may also show whether transfer slabs have been employed.
On current projects, the engineering aspects of the design can be reviewed against the latest IStuctE guidance but for existing buildings, the trail may be less certain. Even though the requirements for Health and Safety Files have been well established for several years prior to the wider adoption of transfer slabs, the information contained in them (even if they can be found) is often lacking.
The difficulty arises in ascertaining whether there are visible signs of distress or specific concerns regarding a building’s condition or design – simply because in a completed building most of the affected areas will be concealed from view either by finishes and furnishings or by suspended ceilings, insulation and so on. Clearly, there will be an onus on surveyors to i) identify whether a transfer slab exists and ii) pay very careful attention to visible areas to see if there is any evidence of cracking, deflection in floors, lack of verticality in columns or other defects that simply raise a tail of suspicion.
Deflection is probably the most common indicator of a problem; with the structure concealed from view, indicators might include ill fitting partitions, windows, doors or furniture elements such as cupboards or desks no longer level or distorted. Deflection can also induce significant bending moments in columns or shear walls hence the need to be vigilant for signs of unusual cracking.
How does the matter affect surveyors?
Given the RICS Practice Alert, regulated firms need to have regard to the nature of the concerns and would be expected to have regard to the guidance available at the time of any survey. This would probably include the identification of a transfer slab (as opposed to a slab designed with downstand beams) and, usually, a recommendation for further enquiry. As RICS warns “RICS members who believe that a building may have a transfer slab, should advise the building owner to instruct a suitably qualified and competent CEng member of the Institution of Structural Engineers or Institution of Civil Engineers, satisfying themselves that such professionals have expertise in this area.”
In addition to the above, and specifically in relation to High Rise Buildings, it is possible that Building Safety Case Reports may need to be re-visited and amended. (vi)
A detailed analysis of a transfer slab is something that is outside the remit of the average Chartered Building Surveyor, but recognition of the form of structure is not and there will now be a reasonable expectation that a surveyor will have flagged the existence or possible existence of this form of construction and made appropriate recommendations for further advice.
More detailed analysis is certainly the remit of a suitably qualified engineer, but they may also be faced with similar difficulties – lack of access, concealed surfaces and so on. There are various measures that should be possible to check - for example strength of concrete and thickness of slab, top and bottom reinforcement etc. Non destructive techniques may help up to a point, but its more difficult and potentially unreliable to determine the nature of the critical shear reinforcement near column bearing and head positions.
Intrusive investigations are unlikely to be helpful, primarily due to the risk that cutting into the slab near to a critical location could cause further weakening; something that would clearly be unsatisfactory. Engineers will probably need to undertake a degree of back calculation to validate the design. However, the answers may still remain inconclusive in which case a period of measurement and monitoring and occasional re-checking may be an appropriate way forward. In the case of HRB’s, the Building Safety Case will need to contain details of the analysis, its conclusions and measures taken (if appropriate) to mitigate any risks.
As noted earlier, transfer slabs have found favour with design and build projects with mixed use developments or developments with say car parking at lower levels. They hold certain advantages in terms of the ease of creating formwork although they are not particularly sustainable forms of construction and consideration needs to be given as to whether the form of construction is appropriate in the first place and whether more conventional arrangements are to be preferred. When involved in project management roles, a surveyor is well placed to advise and inform, possibly influence the construction away from potentially troublesome methods.
The project monitor may not be involved with quality monitoring (making a distinction between bank monitoring roles and monitoring for a purchaser or tenant) but the adoption of a transfer slab is probably something that could have consequences later in the life of a building; the monitor may not have the ability to influence design in the same way as a project manager, but it would be appropriate to flag at least that this form of construction is being used along with an explanation of the potential risks that might be involved.
What about the potential for legal claims?
The question is a difficult one because there are several aspects to consider. First, in terms of negligence claims for failing to identify a transfer slab say during a TDD exercise it may be that a reasonable defence is that until January 2026 (or arguably late 2024) the issue was not well known or understood; a reasonably qualified and experienced surveyor would not necessarily have been aware of the problem and so would not routinely report on it. Post January 2026, and given the RICS Practice Alert, the position may be less clear cut. Of course, if there were reasonable grounds to identify cracking, deflection or even visible signs of punching shear then the position might be different.
Similarly, for designers, non-compliance with the current guide does not necessarily mean that the earlier design was negligent, building standards and practices change all of the time and it is unreasonable to judge performance by comparison with documents that did not exist at the time of construction. The IStructE guide notes that “there will be transfer slabs that were designed before the publication of this guidance which may not comply with all the recommendations in this guide. Non-compliance with this guidance does not necessarily lead to the conclusion that the design of an existing slab is structurally inadequate or statutorily non-compliant.”
Ultimately, each case will be different and will depend upon its own facts.
What are the implications for High Rise Residential Buildings?
The Building Safety case will need to consider the existence of and the design of the transfer slab so that risks can be identified and dealt with. Such an exercise may dictate the need for a certain amount of back calculation by an engineer as well as physical inspection and potentially monitoring. If a problem is identified there may be mitigation measures such as the introduction of strengthening, propping or load reduction. The Building Safety course ought to be reviewed every five years unless there are indications of deterioration in the meantime. Remember that the mere existence of a transfer slab does not mean that a defect will exist.
Conclusion
In summary, while the recent alerts from the Building Safety Regulator, IStructE and RICS highlight legitimate concerns around the design and performance of transfer slabs, it does not necessarily follow that the construction is defective. The alerts serve as a prompt for building owners, surveyors, and engineers to review existing structures and to see that appropriate professional expertise is engaged where uncertainties arise.
By adopting a proportionate, evidence‑based approach—beginning with the identification of potential transfer slabs and escalating to specialist engineering appraisal where justified—the industry can manage risk sensibly while awaiting further clarity from the regulator. Understanding, careful documentation and early engagement with competent structural engineers will be key to ensuring building safety, regulatory compliance, and continued confidence in the built environment.
- https://www.cross-safety.org/uk/safety-information/cross-safety-report/punching-shear-assessments-flat-slabs-supporting-out-1301
- https://www.gov.uk/government/publications/potential-risks-from-transfer-slabs-in-buildings/potential-risks-from-transfer-slabs-in-buildings?deliveryName=DM247793
- https://www.ice.org.uk/areas-of-interest/buildings-and-structures/ice-update-structural-engineering-codes
- https://www.istructe.org/resources/news/istructe-statement-punching-shear-transfer-slabs/
- https://m.servicemail.rics.org/rest/head/mirrorPage/@UzEoPJEU1w60a03AS3z1SUmzGyKvsD9DXbPQ4EriXh8osLjeXGaKnCeyHH5tTgBqTDUn3Swix83YusZsFQvFX5nyK_lLFUhMBjZKuYlYLRCXX7ez.html?deliveryName=DM247793
- https://www.gov.uk/guidance/criteria-for-being-a-higher-risk-building-during-the-occupation-phase-of-the-new-higher-risk-regime