London’s accelerating shift toward structural reuse is reshaping how the capital builds. Office-to-residential conversions, cut-and-carve redevelopments and façade-retention schemes are now standard responses to planning pressure, sustainability targets and land scarcity. Yet while reuse is increasingly presented as the responsible choice, the industry continues to underestimate the structural uncertainty embedded within existing buildings.

At the centre of this issue lies one critical question: how well do we actually understand the structures we are reusing?

Too often, projects rely on desktop studies, historic drawings and visual inspections to justify significant structural intervention. While these methods may satisfy early-stage feasibility, they are fundamentally insufficient when existing frames are altered, loaded differently or partially removed. In a city where many buildings have undergone decades of undocumented change, intrusive surveys are no longer a precautionary extra. They are a necessity.

Existing buildings carry unknowns that new builds simply do not. Load paths may have been altered by previous refurbishments. Reinforcement detailing often differs from original drawings. Concrete strength can vary dramatically across a single floorplate. Steel members may have suffered corrosion or fire exposure that is no longer visible. Temporary works loads during cut-and-carve phases frequently exceed the original design assumptions of the structure itself.

Without intrusive investigation, these conditions remain hidden until construction is underway, when remediation becomes expensive, disruptive and high-risk. Structural failures during refurbishment projects rarely occur in the final condition. They occur during transitional states, when parts of a building are removed, propped or temporarily overloaded. This is precisely where lack of reliable structural data becomes most dangerous.

The Health and Safety Executive has long recognised demolition and alteration works as some of the highest-risk activities in construction. Partial collapse, instability and falls are disproportionately represented in incidents during refurbishment compared to new build projects. Intrusive surveys play a direct role in reducing this risk by allowing engineers to design temporary works and sequencing strategies based on evidence rather than assumption.

From a regulatory standpoint, the stakes have never been higher. The Building Safety Act has introduced long-term accountability for structural safety, particularly in higher-risk buildings. Engineers, contractors and accountable persons are now required to demonstrate that decisions are based on reliable information and competent assessment. Where intrusive surveys are omitted or limited without justification, the resulting gaps in structural knowledge become liabilities that can persist for the life of the building.

Insurance markets are responding accordingly. Professional indemnity insurers are increasingly cautious about projects involving structural reuse, particularly where material substitution or significant alteration is proposed. Lack of intrusive investigation is viewed as an unquantifiable risk, one that cannot be priced or mitigated retrospectively. In practice, this means higher premiums, reduced cover or refusal to insure altogether. The cost of intrusive surveys is small compared to the financial exposure created by proceeding without them.

There is also a growing disconnect between sustainability narratives and structural reality. Reuse is frequently promoted on the basis of embodied carbon savings alone, without sufficient attention to durability, service life and resilience. Intrusive surveys allow engineers to assess whether an existing structure can genuinely support long-term reuse without excessive strengthening, repeated intervention or premature failure. In this sense, proper investigation is not a barrier to sustainability, but a prerequisite for it.

London’s planning environment further complicates matters. Façade retention and partial reuse are often driven by heritage or visual considerations rather than structural logic. This can force design teams into complex load transfers and temporary conditions that significantly increase risk. Without intrusive surveys, these schemes are effectively engineered blind.

The industry is not lacking guidance. Structural institutions and professional bodies consistently emphasise the importance of intrusive investigation in reuse projects. What is lacking is consistent application, particularly at early stages where commercial pressure encourages optimism. Clients are understandably reluctant to invest in surveys before schemes are fully defined. However, the alternative is a false economy that shifts cost and risk downstream, where consequences are far more severe.

This broader issue is explored in greater depth in A Harder Conversation on Risk for London Structural Reuse, which examines how the drive for rapid, sustainable redevelopment is colliding with the realities of ageing structures, regulatory accountability and long-term safety. Intrusive surveys sit at the heart of that conversation, because they define the boundary between informed engineering and hopeful assumption.

As London continues to adapt its existing building stock, intrusive surveys should no longer be treated as optional upgrades to a design brief. They are fundamental to protecting workers during construction, safeguarding occupants long after completion and ensuring that reuse delivers genuine, enduring value.

Structural reuse can be safe, sustainable and successful, but only when grounded in evidence. In a city built layer upon layer over centuries, knowing what lies beneath the surface is not a luxury. It is the minimum standard of responsible construction.