Transfer Slabs and Building Safety: Assessing Risk Following IStructE’s 2026 Update Introduction

In November 2024, the Institution of Structural Engineers (IStructE) published guidance on the design of reinforced concrete transfer slabs, following  concerns around punching shear and prompting increased scrutiny from industry bodies, the Building Safety Regulator (BSR) and building owners. We discussed those developments previously here.

In July 2026, IStructE published a new Q&A and ‘Design and Assessment of Reinforced Concrete Transfer Slabs’ document, providing guidance of how existing buildings may be assessed pending dedicated assessment guidance expected in 2027.

From Design to Assessment

The most significant aspect of the July 2026 guidance is its focus on existing buildings which contain transfer slabs. Whilst IStructE’s November 2024 guidance was primarily concerned with the design of new transfer slabs, the latest publication recognises the industry’s immediate challenge is how to assess and manage transfer slabs in existing buildings.

Given the widespread use of transfer slabs in residential and mixed-use developments constructed in the UK from around 2000 onwards, attention has increasingly turned to the assessment of these structures and the potential management of any associated risks. This is particularly true in the context of higher-risk buildings, where transfer slabs are now receiving increased scrutiny as part of compliance with the Building Safety Act 2022 (BSA).

Punching shear remains the principal concern and continues to highlight the limitations of applying conventional slab design approaches to certain transfer slab arrangements, particularly where supporting and supported columns are closely spaced. However, the guidance makes clear that transfer slab assessment is not limited to punching shear considerations. The IStructE guidance also highlights a range of wider factors, including load redistribution, structural modelling assumptions, long-term structural behaviour and construction-related considerations, reinforcing the need for a holistic approach to assessment.

The IStructE also confirm the development of dedicated assessment guidance, expected in Spring/Summer 2027, which will provide a more comprehensive framework for the assessment, monitoring and remediation of existing transfer slab structures. Importantly, IStructE continues to emphasise that it does not know how many buildings may ultimately be affected and that not all buildings containing transfer slabs will present concerns requiring intervention.

A Risk-Based Approach to Existing Buildings

A central theme to the IStructE’s guidance is that the presence of a transfer slab does not, in itself, indicate a safety issue. Instead, the guidance advocates a risk-based and proportionate approach to assessment. Building-specific factors, the availability of design and construction information and the potential consequences of failure should all be considered when determining whether further investigation is required.

Importantly, a range of potential outcomes are envisaged. Depending on the circumstances, these may range from no further action being required, monitoring and detailed assessment, to remediation or immediate intervention where evidence of distress or elevated risk is identified.

This approach aligns closely with the BSR’s broader emphasis on risk management and taking ‘reasonable steps’, rather than automatically requiring existing buildings to be upgraded to current design standards.

Information Will Be Critical

One of the most significant practical challenges may be the availability of information. The IStructE guidance emphasises that assessment should begin by establishing whether a transfer slab exists, where it is located and how it interacts with the wider structure. Design calculations, reinforcement drawings, construction records and previous inspections may be essential. Where records are missing, investigations may become more intrusive, expensive and uncertain.

 Implications for Building Owners

Building owners are encouraged to establish whether transfer slabs are present within their buildings and to gather relevant design, construction and assessment records. Where transfer slabs are identified, specialist structural advice is likely to be required, particularly in higher-risk residential buildings subject to Building Safety Act obligations.

Even where transfer slabs are ultimately found to be adequate, assessment programmes could generate substantial costs. Disputes may therefore arise long before remediation, including disputes concerning responsibility for investigation costs themselves. The practical challenges of investigating and, where necessary, remediating transfer slabs are often amplified in occupied residential buildings where access is restricted. Residential developments are likely to be of particular significance given the prevalence of transfer slabs from around 2000 onwards and the extended limitation periods introduced by the BSA. Where significant defects are identified, claims may involve structural engineers, design-and-build contractors, main contractors and other consultants or sub-contractors involved in the project.

The IStructE publication also serves as a reminder for those involved in new developments to ensure they remain aligned with current guidance and industry practice relating to transfer slabs. Particular care may also be required when reviewing appointment and contractual obligations, especially where compliance is required with wider standards, guidance or best practice in addition to the applicable design codes.

 Looking Ahead

The July 2026 IStructE publication should be viewed as an interim position rather than a definitive assessment standard. Dedicated assessment guidance is expected in 2027 and may significantly influence future industry practice. Until then, the emphasis remains on proportionality, risk-based assessment and obtaining reliable building information. IStructE continues to stress that transfer slabs are not inherently unsafe and that not all buildings containing them will require intervention.

Transfer slab structures are likely to remain subject to significant scrutiny as further guidance emerges.

If you are assessing a building containing transfer slabs, responding to Building Safety Act obligations, or considering potential recovery of investigation, monitoring or remediation costs, please contact the authors.