Index Linking vs Professional Valuation: What Managing Agents Need to Know.

What Is Index Linking?

Index linking is a mechanism used by insurers to automatically adjust the sum insured each year in line with a construction cost index, typically a variant of the BCIS All-in Tender Price Index or a proprietary equivalent. The intention is to prevent a building from drifting into underinsurance due to general cost inflation.

In practice, the insurer applies a percentage uplift, say 5%, to the existing declared value. No surveyor visits the property. No detailed assessment is carried out. The insured figure simply grows by a fixed multiplier based on a broad market index.

Why Index Linking Alone Isn’t Sufficient.

Index linking has one fundamental limitation: it adjusts an existing figure. If that figure was wrong to begin with, index linking makes it slightly less wrong each year, but never correct.

• It doesn’t account for building changes. Extensions, refurbishments, cladding replacement, new plant. None of these are captured by an index.
• It uses broad national data. Regional labour costs can diverge significantly from a national index, particularly in London and the South East.
• It ignores specialist construction. Listed buildings, non-standard construction, complex M&E. All carry rebuild cost profiles that generic indices cannot model.
• It compounds errors. A figure that was 15% too low in 2018 is still roughly 15% too low in 2024, regardless of how many times it has been uplifted.

BCIS vs Generic CPI.

It is worth noting that not all indices are equal. Some insurers use general CPI as their index-linking basis, which tracks consumer price inflation, not construction cost inflation. These two measures can diverge significantly. Between 2020 and 2023, construction cost inflation substantially outpaced CPI in the UK, meaning that any policy index-linked to CPI over this period is likely to have fallen materially behind actual rebuild cost increases.

The RICS Position.

RICS is unambiguous: index linking is a maintenance tool, not an assessment. Their guidance recommends a full professional reinstatement cost assessment every three years as a minimum, with index linking used only as an interim adjustment between assessments. This position is shared by the ABI and most major brokers.

The Practical Recommendation for Managing Agents.

• Commission a RICS-regulated reinstatement cost assessment at least every three years per block.
• Use index linking only as a bridge between assessments, never as a permanent substitute.
• Document the date and source of the last professional assessment in your management records.
• Treat any insurer query about the sum insured as an immediate trigger for professional reassessment.
• Where the last assessment used a generic online calculator rather than a RICS surveyor, treat the figure as unverified and arrange a proper assessment at the next opportunity.