Choosing the right index for reinstatement cost management: BCIS’s six golden rules 

BCIS indices sit behind many decisions made across the built environment. They are used to track how costs are moving, benchmark projects and adjust prices over time, providing a consistent view of change in a complex market.

In insurance, they play a specific role, with index-linking often relied on to keep the sum insured up to date between formal valuations. But if the wrong index is used, it does not maintain accuracy, it gradually pulls values away from reality, and that is where problems start to emerge.

In most cases, the issue is not a lack of data, but using the wrong measure for the job. So what does ‘getting it right’ actually look like in practice?

Start with what you are trying to measure

Everything else depends on this. For reinstatement costs, the objective is not general inflation or even construction inflation in a broad sense, but the movement in the cost of reinstating a completed building at current market rates. That means capturing the full cost of rebuilding, including labour, materials, preliminaries, overheads and profit, all reflecting current conditions.

It is therefore not CPI (Consumer Prices Index), not just input costs and not the price of a single material that happens to be volatile. For a house, it is the cost to rebuild that house, while for a commercial building it is what it would actually cost to deliver a comparable asset in today’s market. If that definition is not clear from the outset, everything that follows risks being built on the wrong foundation.

Then match the index to that objective

Once the objective is clear, the next step is to choose an index that reflects it. For residential property, the ABI/BCIS House Rebuilding Cost Index (HRCI) is designed for exactly this purpose, capturing whole-building movement and aligning directly with how reinstatement cost is assessed in practice. The HRCI is also used to update the BCIS rebuilding cost models between publications, and so it is widely used across the UK insurance market.

Looking at what does not work helps make the point. CPI  measures household spending rather than construction, while a materials index shows what is happening to inputs but not what it costs to actually rebuild. Even broader construction indices can miss housing-specific dynamics.

For non-residential property, the picture shifts slightly, as larger and more complex buildings are more influenced by procurement routes and market conditions. In these cases, indices such as the BCIS All-in Tender Price Index (TPI) are often more appropriate, as they reflect what contractors are actually pricing in the market, including labour, materials, overheads, profit and the wider commercial environment. The TPI is used to update BCIS Average Prices, which can be used where a more building-type-specific view is needed. The key question to keep coming back to is whether the index reflects the cost you are trying to track.

Make sure the index works in practice

Index-linking is not just a theoretical exercise, it needs to stand up in real-world use.

That means the index should be published regularly, supported by a clear and transparent approach to revisions, and consistent over time. Users should understand whether figures are provisional, when they are updated and how changes are handled, particularly where values are being automatically uplifted.

This matters more now than ever. Under Consumer Duty, it is not enough for an index to exist, it has to be appropriate, explainable and defensible. If you cannot clearly explain how the index works and why it is being used, that is usually a sign that something is not quite right.

Understand what sits behind the numbers

You do not need to be an indices specialist, but you do need to understand what is driving the figures you are using. Different indices are constructed in different ways. Some track merchant prices, such as the HRCI, others reflect factory gate costs, such as the BCIS General Building Cost Index (GBCI), while tender price indices (TPI) capture the prices agreed between client and contractor.

Reinstatement cost brings all of these elements together, as it is influenced not only by input costs but also by preliminaries, contractor margins and market capacity. Indices such as the HRCI and BCIS All-in TPI capture that broader picture, whereas others only reflect part of it. If you are using an index that represents just one slice of the cost, you are potentially only seeing part of the movement.

Read the notes, they matter more than you think

It sounds simple, but it is often overlooked. BCIS indices are clearly labelled, with notes explaining what they measure and how they should be used, and this context is essential rather than optional. Using an index outside its intended scope is one of the easiest ways to introduce error, even if it is not immediately obvious.

Over time, the gap between indexed values and real costs will grow, and a small misalignment can become a significant issue. Spending a few minutes checking definitions at the outset can prevent that drift from developing.

Do not be guided by what feels comfortable

This is where decisions can start to drift away from the underlying objective.

When markets are volatile, there can be a temptation to favour indices that appear more stable or produce smaller increases, particularly where there is sensitivity around cost or premium. However, that is not the right test.

The real question is whether the index is reliably measuring reinstatement cost. If it is, then short-term volatility is simply part of the reality it is capturing. Avoiding that volatility does not remove the risk, it just masks it.

Why this matters

Used properly, BCIS indices provide a clear and consistent view of how costs are moving, allowing professionals to spend less time interpreting data and more time applying judgement. In the context of reinstatement cost, that means supporting a sum insured that reflects real-world rebuilding costs, rather than an approximation that drifts over time.

The principles are straightforward, but they matter. Be clear about what you are measuring, choose an index from a reputable provider that aligns with it, understand how it works and apply it consistently. Get those right, and indexation does what it is meant to do, keeping values grounded in reality as the market moves.

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