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What are transfer slabs, and what should be done about them?
Andrew Lawrence, a fellow at engineering consultancy Arup, a structural engineer and expert in building safety, has been involved in the assessment of a large number of structures with transfer slabs. As the sector attempts to quantify the risk posed by this latest frontier in the building safety crisis, Peter Apps catches up with him to ask what should be done
What are transfer slabs, and what should be done about them? #UKhousingPeter Apps catches up with Andrew Lawrence, a structural engineer and expert in building safety, to find out what should be done about transfer slabs #UKhousingWhat should building owners be doing to mitigate the risk of transfer slabs? Are there particular building types or eras that are particularly at risk?
Modern, larger concrete buildings are typically supported by ‘columns’ running continuously from the top of the structure down to the ground. In some cases, column positions need to change between floors – for example, to accommodate open retail space or a basement car park. We’ve all seen old car parks and supermarkets with columns in awkward places. In modern buildings, we try to avoid this to make the buildings easier to use.
A ‘transfer structure’ is used to redistribute loads from the columns above to those below. This transfer can be achieved using beams or slabs. Reinforced concrete transfer slabs are often preferred as they avoid the deep beams that can reduce headroom.
However, transfer slabs must be very carefully designed to ensure they are strong enough to resist ‘punching shear’, a critical failure mode where the concentrated load being carried down the column will try to ‘punch’ through the slab or beam transferring this load.
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Transfer slabs have become increasingly common in the past 25 years, particularly in mixed-use developments, buildings with podium levels and schemes incorporating retail or parking at lower levels. Recent findings indicate that transfer slabs in some buildings may not achieve the strength originally intended.
In most cases, this does not necessarily represent an immediate safety issue due to the inherent safety margins (factors of safety) in design codes. However, in some cases the ‘factor of safety’ will be significantly lower than intended and intervention will be needed.
This issue was highlighted by the Building Safety Regulator in its December 2025 advisory, which stated that it is currently investigating the risks and will provide further advice in due course. In the interim, the regulator has called on building owners to identify whether transfer slabs are present and seek expert assessment by a competent structural engineer where necessary.
I completely support this and would add that owners should also seek to obtain as much structural design and construction information about their buildings as they reasonably can. This is consistent with the wider existing requirement to maintain a robust ‘golden thread of information’, particularly for higher-risk buildings (HRBs).
What warning signs could be early indications of a bigger problem with transfer slabs – or a serious structural issue?
Transfer slab deficiencies are typically not visible and are most reliably identified through a detailed assessment of the building’s design by a specialist structural engineer.
In some cases, warning signs may appear in the form of unusual crack patterns in the concrete slabs. While periodic structural inspections are good practice – particularly as part of HRB safety case preparation – visual checks alone are unlikely to identify transfer slab risks.
Cracking in concrete slabs is common and is usually not problematic, and so distinguishing between benign cracks and cracks that would indicate a concern requires specialist expertise from a competent structural engineer to determine whether further investigation is necessary.
What are the options for remediation if a transfer slab issue is found, and how long can it typically take?
If a concrete transfer slab is found to be significantly understrength, there are a number of potential solutions available. One is to provide local strengthening around the top of the column – a so-called ‘drop head’. Another is to install new columns immediately below the affected areas and thereby reduce the load carried by the slab.
However, remediation strategies are highly building-specific and depend on factors such as the degree of understrength, structural layout and accessibility, as well as occupancy or operational constraints.
As a result, the strengthening needed (if any) and the time to undertake those works can vary significantly – from relatively localised works to complex structural modifications requiring careful phasing – and will be completely different in different buildings.
How widespread are problems with transfer slabs?
There is currently no industry-wide data on the prevalence of transfer slab deficiencies. The issue is under active review by the Building Safety Regulator, and further guidance is expected in due course.
What changes need to be made to processes to mitigate against similar issues in the future?
Reducing the risk of structural safety issues of this nature requires a combination of stronger oversight, clearer accountability and more robust checking processes.
Based on Arup’s internal research, the most effective measure would be the introduction of rigorous and independent checking of structural designs by a separate firm of engineers. This approach is already standard practice in the UK for infrastructure projects and in several international markets for larger buildings.
While this might be perceived as expensive, it would add less than 1% to the cost of a new building. Given the potential cost and disruption associated with remediation, this represents a proportionate and effective risk reduction measure.
Transfer slabs are not inherently unsafe, but they are a critical structural element that requires rigorous design, checking and oversight. The priority for building owners is understanding whether these slabs are present and ensuring they have been properly designed.
Read about the risk transfer slabs pose to resident safety
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