The meaning of subsidence (at least in the insurance and legal context) owes far more to post-war lending practices and reputational risk than to geotechnical science.
Understanding how we got here explains much of the confusion, disagreement, and litigation that still surrounds subsidence claims today.
POST-WAR LENDING AND THE BIRTH OF “SUBSIDENCE” COVER
During the vast house-building programmes of the 1950s and 1960s, mortgage lenders advanced extraordinary volumes of lending. In the overwhelming majority of cases, this caused no difficulty at all.
However, lenders imposed one crucial condition: borrowers were required to insure their homes with a reputable insurer. In practice, this often meant an insurer tied to, or approved by, the lender. Homeowners had little genuine freedom of choice, and policies had to meet lender-mandated terms.
These household policies covered familiar risks — fire, flood, storm, vehicle impact — but they did not initially address serious structural instability or foundation failure. When such failures did occur, the consequences were stark.
Media coverage frequently showed families standing in front of collapsed or condemned homes, still burdened by substantial mortgage debt. The reputational damage to lenders and insurers alike was severe.
The solution was pragmatic rather than technical: lenders insisted that insurers include an additional peril —“subsidence” — later supplemented by “heave” and “landslip.”
A TERM WITHOUT A TECHNICAL DEFINITION
Crucially, these new risks were never properly defined in engineering terms.
Subsidence was introduced as a label, not a diagnosis. Heave followed, again without technical clarity. Landslip was included in only the vaguest sense.
At the same time, the term “settlement” began to appear in insurance discourse. For policy purposes, it was often treated as a form of subsidence — despite the fact that, in geotechnical terms, settlement is a fundamentally different phenomenon.
This early lack of precision embedded ambiguity into policies that persists to this day.
THE 1975–76 DROUGHTS: FROM MARGINAL RISK TO SYSTEMIC PROBLEM
The situation was then dramatically compounded by the exceptionally dry summers of 1975 and 1976.
During this period, tens of thousands of properties suffered damage, particularly those founded on shrinkable clay soils. Claim volumes rose rapidly, and insurers were forced to confront subsidence not as a rare anomaly but as a widespread, climate-driven risk.
Contemporary industry guides from that period include striking graphs showing the rapid accumulation of claims — a clear demonstration of how suddenly subsidence became a dominant issue in domestic property insurance.
PROFESSIONAL GUIDANCE AND THE ROLE OF THE EXPERT WITNESS
In 2016, I was asked to prepare a paper for the Institution of Civil Engineers on the role of the expert witness, written from the expert’s perspective.
Pages 2 and 3 of that paper are particularly relevant here, as they set out the historical background to the subsidence guidance that followed. The paper was later reproduced in at least one other professional publication.
THE ISTRUCTE SUBSIDENCE GUIDES (1994 AND 2000)
Any serious discussion of subsidence must also acknowledge the two seminal publications issued by the Institution of Structural Engineers:
Subsidence of Low-Rise Buildings (March 1994)
Subsidence of Low-Rise Buildings – Second Edition (August 2000)
The first edition proved highly influential. The second followed relatively quickly, responding to how the original guidance had been received and applied in practice.
WHY THIS HISTORY STILL MATTERS
This is not merely academic background. The way subsidence entered insurance policies explains:
- why definitions remain blurred,
- why experts and insurers sometimes speak past one another, and
- why courts are so often asked to resolve disputes rooted in terminology rather than engineering reality.
Subsidence, as we encounter it today in claims and litigation, is as much a product of post-war finance and insurance pragmatism as it is of soil mechanics.
Understanding that origin story is essential if we are to deal with subsidence disputes clearly, fairly, and intelligently.
