Key facts: Rebuild cost is the price of reconstructing your home from scratch — demolition, materials, labour, professional fees. It's often lower than market value (which includes the land) but can be higher for period, listed or non-standard homes. Underinsurance triggers the average clause: insure for half the true figure and insurers can halve every claim, not just a total loss.
Two numbers doing different jobs
Market value answers "what would this sell for?" — land, location and demand included. Rebuild cost answers "what would it cost to put this exact building back?" The land doesn't burn down, so insurance only needs the second number. In much of the country rebuild sits below market value (over-insuring wastes premium); for stone cottages, listed buildings and London-priced plots the relationship flips in either direction — assumptions are the enemy.
Finding your rebuild figure
Three routes, in rising accuracy: the rebuild figure in your mortgage valuation or previous policy (check its age); the free BCIS/ABI rebuild calculator for standard construction; and a professional reinstatement assessment by a surveyor — the right answer for period, listed, extended or non-standard homes, where generic calculators genuinely mislead. Our listed buildings guide covers why heritage rebuilds cost multiples of modern equivalents.
The average clause — how underinsurance bites
Underinsurance doesn't just cap catastrophe payouts; it shrinks ordinary ones. Declare £200,000 against a true £400,000 rebuild and you're 50% insured — so a £20,000 kitchen-fire claim can be settled at £10,000 under the average clause. This proportional penalty is standard across the market and is how families discover, mid-claim, that years of premium bought half a policy. When in doubt, err higher or use policies with unlimited/blanket sums.
Keeping the number current
Reassess after extensions or major renovations, when building-cost inflation runs hot (recent years moved rebuild costs sharply), and every few years regardless. Many policies index-link the sum insured — helpful drift protection, but index-linking a wrong starting number preserves the error faithfully. Extensions are the classic gap: £60,000 of new kitchen-diner, insurance never told, average clause armed.
Getting cover that would actually rebuild your home
A specialist can sense-check your rebuild figure and place cover suited to your construction type — see best buildings insurance options, or compare home insurance through Nesto — free, no obligation.
Frequently asked questions
Is rebuild cost higher or lower than market value?
Usually lower — land value isn't rebuilt. But period, listed and non-standard homes can cost more to rebuild than to buy. Check, don't assume.
What happens if I'm underinsured?
The average clause lets insurers reduce every claim proportionally to the shortfall — a 50% underinsured home can see all claims halved.
How do I calculate my rebuild cost?
The free BCIS calculator for standard homes; a surveyor's reinstatement assessment for anything period, extended or unusual.
Does my rebuild cost change over time?
Yes — with building-cost inflation and any works you do. Index-linking helps, but reassess after extensions and every few years.