How the two differ in kind
Two numbers describe the same house and they are not interchangeable. Insuring against the wrong one is one of the most common and most consequential errors a property owner makes, and it goes wrong in both directions.
MARKET VALUE is what a buyer would pay. It is dominated by location, by the state of the market, and by the LAND the building stands on — and land is not something an insurer replaces, because it does not burn down, blow away or flood beyond recovery in the sense a building does.
REBUILD COST, also called reinstatement cost, is what it would take to construct the same building again on the same plot after a total loss. It is a construction estimate rather than a valuation, and it includes several things people leave out: demolition and clearing the site of what is left, the building work itself at current prices, professional and local authority fees, and compliance with the regulations in force NOW — which for an older building can be a substantially different and more expensive building than the one that stood there.
The two diverge in both directions and the consequences differ. In an expensive area with ordinary construction, market value is far the larger figure, and insuring for it means paying premium on a sum that could never be claimed. In a cheaper area, or for a building that is large, elaborate, listed, or built with materials and craftsmanship that are expensive to reproduce, rebuild cost can exceed market value comfortably — and a policy set to market value is then UNDERINSURED.
Underinsurance is the expensive direction, because of how most policies settle it. Where the sum insured is materially below the true rebuild cost, many policies apply proportional settlement — sometimes called average — reducing every claim by the proportion of the shortfall. A partial claim, not just a total loss, is paid at that reduced proportion. So the penalty for a sum insured set at half the correct figure is not felt only in a catastrophe; it applies to the kitchen fire as well.
The factors that actually differ
Show
| Rebuild (reinstatement) cost | Market value | |
|---|---|---|
| What it measures | The cost of constructing the building again after a total loss. | What somebody would pay for the property as it stands. |
| Does it include land | No. Land is not replaced and does not belong in a sum insured. | Yes, and in many locations the land dominates the figure. |
| What drives it | Floor area, construction type, complexity, finishes, site access, and current building costs. | Location, market conditions, condition, and comparable sales. |
| Regulations | Today's, which for an older building can mean a materially different and dearer rebuild. | Irrelevant to the figure. |
| Extras that belong in it | Demolition and site clearance, professional fees, local authority fees, and often outbuildings, boundary walls, drives and landscaping. | None — it is a single valuation. |
| Where it is the larger number | Cheaper areas, and for large, elaborate, listed or unusually constructed buildings. | Expensive areas with ordinary construction, where land dominates. |
| Consequence of insuring to it wrongly | Not applicable — this is the correct basis. | Either wasted premium, or underinsurance and proportional settlement on every claim. |
| Who produces it | A surveyor's reinstatement cost assessment, or an indexed rebuilding-cost calculator for a standard property. | An estate agent or a valuer, for a different purpose entirely. |
| How often it should be revisited | Regularly — construction costs move, and they have moved sharply in recent years. Index-linking helps and is not a substitute. | Whenever you are selling, which is not the same schedule. |
| Effect of an extension | Rises immediately, and this is the most common reason a sum insured falls behind. | Also rises, but nobody tells the insurer because it is not a sale. |
Which one, and when
Choose rebuild (reinstatement) cost when…
- Setting or reviewing the sum insured on a buildings policy — this is the only correct basis.
- After any extension, loft conversion, garage or outbuilding, which changes it and is the classic cause of drift.
- For an older, listed or unusually constructed building, where the figure needs a surveyor rather than a calculator.
- At a regular interval, because construction costs move independently of house prices.
Choose market value when…
- Selling, buying, or borrowing against the property.
- Assessing whether an improvement is worth making, which is a return-on-investment question.
- Anything to do with equity, mortgage or tax.
- As a cross-check only — a large divergence in either direction is worth understanding rather than acting on.
Now run your own numbers
This page holds no prices on purpose — a national average is wrong for almost every real project. Quantify both options with your dimensions and your local quotes.
Frequently asked questions
- Why is the land excluded?
- Because insurance replaces what is lost, and a fire, storm or flood does not remove the land. After a total loss the plot is still there, and what has to be paid for is clearing it and building again on it. That is why a sum insured based on market value is usually far too high in an expensive location: a large share of what a buyer pays is for the ground and the address, neither of which any claim would replace. The corollary catches people out in the other direction — in a location where land is cheap, the market value may be mostly the building, and if that building is large or elaborate the rebuild cost can exceed the market figure comfortably. Neither situation is unusual, which is why the correct basis is a construction estimate rather than a proportion of a valuation.
- What is proportional settlement and why does it matter?
- A clause in many policies — often called average — under which, if the sum insured is materially below the true rebuild cost, every claim is reduced by the proportion of the shortfall. The critical point is that it applies to PARTIAL claims, not only to total losses. So a property insured for half its correct rebuild cost may see a modest claim for fire or water damage settled at around half, even though the sum insured comfortably exceeds the amount being claimed. That is the mechanism by which underinsurance hurts in the ordinary case rather than only in a catastrophe, and it is why the sum insured has to be right rather than merely large enough to cover what you imagine going wrong. Terms vary between policies and jurisdictions, so the wording is what governs.
- What does a rebuild cost include beyond the building work?
- Several things that are routinely omitted and that together are a significant proportion. Demolition and site clearance, since what is left after a loss has to be removed and disposed of. Professional fees — architect, engineer, surveyor, and local authority charges for the approvals a rebuild requires. Compliance with the regulations in force at the time of rebuilding, which for an older building can mean insulation, means of escape, and structural standards that materially change the cost. Site access, which on a constrained or awkward site raises costs considerably. And everything outside the walls that a policy covers: outbuildings, garages, boundary walls, drives, paths, patios and sometimes landscaping. A figure that covers only the house's floor area at an average build rate is likely to be well short.
- How often should the figure be reviewed?
- More often than most people do, and specifically after anything that changes the building. Construction costs move independently of house prices and have moved sharply in recent years, so a sum insured set some years ago and left alone can be substantially behind even with nothing built. Most policies apply index-linking automatically, which helps and does not solve it: an index tracks general cost movement but knows nothing about the extension, the loft conversion, the new outbuilding or the expensive kitchen. Those are the changes that cause real drift, because they are exactly the moments when nobody thinks to tell the insurer — there is no sale, no mortgage event and no prompt. A review after any significant work, and a periodic reassessment otherwise, is the practice that avoids the problem.
- When do I need a surveyor rather than a calculator?
- Whenever the building is not typical, which is a wider category than it sounds. An indexed rebuilding-cost calculator works from floor area, construction type, region and age, and it is calibrated on standard modern housing — so it is reasonable for a standard modern house and progressively less reliable as the building departs from that. The cases that need an assessment are listed and historic buildings, where reinstatement may require matching materials and traditional craftsmanship at a cost unrelated to modern construction; unusual construction, including timber frame, steel frame, non-standard materials or thatch; large or architecturally complex properties; anything with significant outbuildings, walls or landscaping; and constrained sites where access alone changes the cost. A reinstatement cost assessment is a modest one-off expense against the exposure it quantifies.
- What if the rebuild cost is higher than the market value?
- Insure for the rebuild cost, and do not be talked out of it by the apparent illogic of insuring a building for more than it would sell for. The two numbers answer different questions, and the insurance one is what it would cost to put the building back — which for a large, elaborate or traditionally built property in a low-value area can genuinely exceed what a buyer would pay for it. Setting the sum insured at market value in that situation is straightforward underinsurance and exposes every claim to proportional settlement. The situation is common enough to have a name in the trade, and it is a routine finding of reinstatement assessments on period property. If an insurer questions the figure, an assessment is the document that settles it.
- Does this apply to contents as well?
- The same principle applies with a different basis, and it is worth separating because the two sums are insured independently. Buildings cover is on reinstatement cost as described; contents is on the cost of replacing possessions, usually as new for new where the policy provides it. The recurring error mirrors the buildings one: people estimate what their possessions are worth second-hand rather than what replacing them would cost, and under-declare accordingly — with the same proportional settlement consequence. The practical method is the same too: go room by room rather than guessing a total, note high-value items separately since most policies cap individual items unless specified, and revisit it after any significant purchase. Neither exercise is interesting, and both are cheap relative to discovering the gap at claim time.
- What about the cost of alternative accommodation?
- It is normally a separate benefit in the policy rather than part of the sum insured, and it is worth checking what limit applies because a rebuild takes longer than people expect. After a total loss the sequence is insurer assessment, demolition and clearance, design and approvals, procurement and then construction — a period measured in many months and often longer than a year for anything substantial, and longer still for a listed building or a constrained site. Cover for alternative accommodation is usually expressed as a percentage of the buildings sum insured or as a fixed amount, and a limit that looked generous can be consumed by a lengthy rebuild in an expensive rental market. It is one of the few policy details worth reading before a claim rather than during one.