Sums insured

Buildings Underinsurance and Reinstatement Cost, Explained

In short: Buildings must be insured for their full reinstatement cost — the cost of clearing the site and rebuilding, plus professional fees — not their market value, and the two figures are often very different. If the sum insured falls short, the average clause lets insurers reduce every claim in proportion, so even small claims are underpaid. Apex Insurance Brokers is an independent, FCA-authorised UK broker (FRN 724952) that helps property owners get the sum insured right and keep it right.

Reinstatement cost, not market value

The single most important number on a buildings policy is the sum insured, and the single most common mistake is basing it on the wrong thing. Buildings should be insured for their full reinstatement cost: what it would actually cost to put the building back after a total loss. Market value — what the property would sell for — is a different number driven by location, land value, rental yield and demand, and it bears no reliable relationship to the cost of rebuilding. A modest building in an expensive area can have a market value far above its rebuild cost; a listed or period building in a cheap area can cost far more to reinstate than it would ever sell for. Neither direction is safe to guess.

What full reinstatement actually includes

Reinstatement is more than bricklaying. A properly constructed sum insured allows for:

Demolition and debris removal — a badly damaged building must be made safe, taken down and cleared before rebuilding can start, and the cost sits with the owner.
The rebuild itself — materials and labour to current standards, including compliance with building regulations that may not have applied when the building was first constructed.
Professional fees — architects, structural engineers, quantity surveyors and project managers are all needed to design and deliver a reconstruction, and their fees form a meaningful part of the total.

Features that make a building distinctive make it more expensive to reinstate: listed status, stone or period brickwork, non-standard construction, and restricted site access all push the figure up. A sum insured lifted from an old policy schedule, a mortgage valuation or a guess rarely captures any of this.

How average punishes underinsurance

Underinsurance does not just bite on a total loss. Most commercial property policies contain an average clause (also called proportionate reduction): if the sum insured is less than the full value at risk, the insurer reduces the claim payment in the same proportion — on every claim, however small. A building insured for half its true reinstatement cost does not merely risk a shortfall if it burns to the ground; a routine escape-of-water claim on that same building can be cut back too, because the insurer has only ever received a premium for part of the risk. We explain the mechanism in detail in our guide to how the average clause works. The practical consequence is that underinsurance is not a quiet economy; it is a discount on your own claim, discovered at the worst possible moment.

Day-one uplift: how policies handle inflation

Rebuilding costs move over time, and a claim can take years to settle from the date the sum insured was last set. Many commercial policies address this with a day-one uplift (or day-one reinstatement) basis: the policyholder declares the reinstatement cost as at the start of the policy — the declared value — and the policy provides an agreed margin of inflation protection above that figure for cost increases between setting the value and completing the rebuild. The crucial point is that the uplift protects against inflation after the declared value was set; it does not rescue a declared value that was wrong on day one. If the starting figure is understated, average can still apply to it, uplift or no uplift.

The fix: periodic reinstatement cost assessments

The dependable cure for underinsurance is a professional reinstatement cost assessment: a survey by a qualified assessor — typically a chartered surveyor — who measures the building and calculates the full reinstatement cost, including demolition, fees and modern compliance requirements. From that baseline, the figure should be reviewed periodically and refreshed after anything that changes the building: extensions, refurbishment, change of use, or significant movements in construction costs. For a portfolio, assessments can be cycled across the properties so each is professionally revisited in turn. An assessment also gives you strong evidence, if a claim is ever questioned, that the sum insured was set diligently.

Where a broker comes in

A broker cannot set your rebuild cost for you — that is the assessor’s job — but a good one will check the basis of cover is right, make sure fees and debris removal are allowed for, arrange day-one uplift terms where appropriate, flag schedules that look light against the property description, and connect you with assessors. As an illustrative scenario rather than a real claim: an owner who insured a converted Victorian warehouse at the figure in a dated mortgage valuation, then suffered a serious fire, could face both a shortfall against the true rebuild cost and a proportionate reduction on the settlement — a double penalty that a single professional assessment would have prevented.

Frequently asked questions

My market value is higher than my rebuild cost — am I safe?

Not automatically. You may be over-insured, paying premium on a figure higher than the insurer would ever need to pay out, which is wasteful. And the relationship can be deceptive: the sale price includes the land, which does not burn. The only reliable route is to have the reinstatement cost assessed in its own right rather than inferred from what the property is worth.

Does the average clause apply to small claims too?

Yes. That is what makes it so painful. Average applies proportionate reduction to any claim where the sum insured is found to be inadequate, not just to total losses. An underinsured building is underpaid on every claim it ever makes.

How often should the reinstatement cost be reassessed?

There is no single rule, and we deliberately avoid quoting one: the right rhythm depends on the building, how construction costs are moving and whether the property has been altered. The principle is that a professional assessment should be obtained as a baseline, reviewed regularly, and refreshed promptly after extensions, refurbishment or changes of use. Your broker can help you set a sensible review cycle for your property or portfolio.

Apex Insurance Brokers Limited is authorised and regulated by the Financial Conduct Authority (FRN 724952).