Reinforced concrete transfer slabs have become a growing focus for regulators, structural engineers, and insurers following concerns about the adequacy of some historic designs. While no widespread issues have been identified in residential buildings, the increased scrutiny has raised questions as to whether certain developments could require further assessment and potential remediation.
This article examines the potential liability implications for design and construction professionals, and considers how they should prepare for regulatory and insurer enquiries.
What are transfer slabs?
Reinforced concrete transfer slab are used to redistribute vertical loads within a building. Acting as a critical structural interface, they enable loads from upper floors and columns to be transferred safely to alternative supports beneath.
Transfer slabs have been a common feature of UK construction since the early 2000s. They are typically found in high-rise residential and mixed-use developments where the structural arrangement above does not directly align with the supporting structure below.
Why are transfer slabs under scrutiny?
In November 2024, the Institute of Structural Engineers (IStructE) published new guidance (opens a new window) on the design of reinforced concrete transfer slabs, highlighting what it described as a significant industry-wide knowledge gap. The publication of this guidance has prompted questions about the adequacy of some designs completed before its release, and whether the underlying calculations fully reflected the behaviour of these complex structural elements. Subsequently, both CROSS-UK (opens a new window) and the Building Safety Regulator (BSR) (opens a new window) have raised concerns about potential design issues.
Particular attention has focused on the risk of ‘punching shear’ failure, where a concentrated load can cause a supporting column to punch through a slab – likened a pencil being pushed through a sheet of paper. In such cases, relatively small errors in structural modelling, load assumptions, or detailing can have disproportionately severe consequences.
Historically, many reported punching shear incidents have involved car parks and other non-residential structures. While there is currently no evidence of widespread failures in residential buildings, the BSR and industry bodies are concerned that similar design vulnerabilities may exist in some residential developments.
Implications for design and construction professionals
Residential buildings may fall within the scope of the Defective Premises Act 1972, which now benefits from extended limitation periods of up to 30 years under the Building Safety Act (BSA) 2022. This contrasts with many RAAC-related claims, which typically involved non-residential buildings and therefore often fell outside the Defective Premises Act regime.
For design and construction professionals, this creates a materially different and potentially wider liability exposure. Concerns regarding the adequacy of historic designs could lead to requests for further assessment, intrusive investigations, or remedial measures, even where no structural failure has occurred. In particular, challenges to historic design assumptions, modelling approaches, and detailing decisions may increase the potential for professional negligence allegations.
Where remedial works are required, the costs involved may be significant, particularly in occupied residential buildings where investigations and structural interventions can be complex and disruptive. The scale of these potential costs may increase the financial exposure associated with any claims arising from affected developments.
Managing insurance and liability exposures
Further assessment guidance is anticipated in 2027, making this an evolving area that insurers, developers and construction professionals should continue to monitor closely.
Nevertheless, as scrutiny of transfer slab design continues to increase, organisations involved in residential and mixed-use developments may be asked by insurers to demonstrate how potential risks were identified and managed. Firms should therefore consider taking the following steps to improve their understanding of any potential exposure and ensure they are prepared to respond to future enquiries:
Preserve design calculations, drawings and supporting records
Consider reviewing historic projects where transfer slabs were used, particularly in residential or mixed-use developments
Assess whether adequate documentation is available to support future investigations or regulatory enquiries
For more information, reach out to a member of our team.
