July 2026
What is a transfer slab, where are they found and why are they important?
A transfer slab is a flat, thick, concrete plate that is used to transfer column loads in buildings when the columns above and below don’t align. They are important because they tend to support large areas of building.
Why have concerns emerged over transfer slab design? What information should the public be made aware of?
Research by the IStructE and recent investigations into UK residential developments have exposed weaknesses in the design of transfer slabs, a widely used but complex structural solution. In 2024 IStructE published guidance on the design and construction of new build transfer slabs. This guidance addressed the historically lack of code coverage and a consistent industry-wide design approach, particularly for behaviours such as load redistribution and punching shear.
Is this just a UK problem or an international issue?
Our November 2024 guidance has been downloaded thousands of times across the globe, showing that transfer slabs are used internationally. The lack of code coverage and general guidance indicates that this issue is not confined to the UK.
Do we know how many buildings are affected?
The IStructE does not collect building data. However, we believe that transfer slabs have tended to be found in concrete, mixed use residential buildings, hotels and some commercial buildings from around 2000 onwards. Not all transfer slabs will be an issue.
What is punching shear and why is it critical?
In design of plates and beams are generally we are concerned with two types of failure; bending when an element curves and flexes and shear, when it snaps. Punching shear is a special case of shear when a column or point load punches through a plate. Unlike bending failure, punching failure can be sudden and with little warning.
Punching shear risk and under-reinforcement have been Identified as critical transfer slab failure modes. What does this mean?
Punching shear at column–slab connections is recognised as one of the most significant risks in transfer slab design. The November 2024 IStructE guidance stresses that punching shear behaviour in transfer slabs differs markedly from typical slab systems, requiring advanced analytical approaches and a high level of engineering judgement. Defects in this area — such as insufficient reinforcement at column loactions — can lead to localised failure with limited warning.
Have any buildings collapsed due to punching shear failure in transfer slabs?
Failure requires a trigger event, such as overloading, degradation or damage. A punching shear failure would not necessarily lead to a building collapse if the load can redistribute around the structure. For example, The US Surfside (Champlain Towers) collapse was understood to have been instigated by a punching shear failure due to overloading and corrosion, but signs were evident leading up to the event.
Would there be signs of failure beforehand?
Punching shear is a brittle failure, which can occur without warning, but often is indicated in cracking around columns, or at columns. If a structure is redistributing load then deflection and cracking in finishes and walls around the transfer slab may occur. Where these are seen, immediate action should be taken.
Why was a block in East London Estate recently evacuated?
The evacuation of residents from buildings at the Stratford Halo development was understood to have been undertaken as a precautionary measure following inspections which revealed evidence of overstress.
What advice do you give to building owners and managers?
The BSR has issued advice to building owners and Principal Accountable Persons (PAPs). For those responsible for a building of the type and age affected, we would first advise that it should be confirmed if a transfer slab is present or not. If a transfer slab is present, we would recommend that it is assessed. IStructE is currently preparing guidance specifically for assessment of existing transfer slabs. In the meantime, there are several IStructE guides that can be used to gauge the safety of transfer slabs, alongside the application of engineering judgement:
What does the November 2024 IStructE guidance recommend on transfer slab design?
In 2024 IStructE published the first technical guidance addressing a major knowledge gap in transfer slab design. At the time of publishing, it highlighted the absence of unified standards — especially for punching shear in transfer slabs— calling for improved understanding of the topic across the industry. Engineers are required to understand complex behaviours, construction sequencing, and disproportionate collapse mechanisms. The IStructE guidance sets out a robust design approach for new build transfer slabs and gives recommendations for dealing with construction and sustainability issues.
The November 2024 guide is for new build only. Is further guidance for existing slabs planned?
The November 2024 guide sets out a robust approach for the design of new build structures. It is not intended to cover existing structures, which need to be assessed on a case by case basis. IStructE has assembled a task force from academia and industry to produce guidance on the assessment of existing transfer slab structures.This involves carrying out research into the issues identified and advice on analysis, assessing risk and remediation. Given the complexity and sensitivity of the task, this guidance is due for publication in spring/ summer 2027.
In the meantime, IStructE have provided a new PDF on the Design and Assessment of Reinforced Concrete Transfer Slabs, published in June 2026. This outlines the approach that our guidance will take and we will provide updates to assist those already carrying out assessments:
- Design and assessment of reinforced concrete Transfer Slabs: Provides a summary of the issues around transfer slabs, describes the design and assessment approach
- Assessing higher-risk buildings under the Building Safety Act: a compendium of structural typologies: Summarises common structure types and potential; issues, including those with transfer slabs
- Preparing safety case reports for higher-risk buildings under the Building Safety Act: guidance for structural engineers: Sets out the process for assessing the safety of existing building structures, including those with transfer slabs.
- Design of transfer slabs: Describes the issues with transfer slabs are and sets out the design approach for new structures.
- Appraising factors of safety in existing engineered structures: Provides guidance on checking the safety of existing structures.
Further information from the BSR building safety toolkit can be found here: Building safety toolkit - Making Buildings Safer),
IStructE’s June 2026 Design and Assessment of Reinforced Concrete Transfer Slabs, can be accessed here: