How do I know if my buildings insurance is enough to rebuild my house?

Check the sum insured figure on your policy schedule against a proper rebuild cost estimate, not the price you paid for the house. The free ABI/BCIS calculator at abi.bcis.co.uk takes about ten minutes and asks for your property type, floor area, number of storeys and any non-standard features, then returns a reinstatement figure based on the same BCIS data insurers use. If your policy's sum insured is more than about 10% below that figure, ask your insurer to update it before renewal rather than waiting for a claim to reveal the gap. This matters most for older, listed, or non-standard properties, where rebuild cost can run well above a simple per-square-metre guess, and for anyone who has extended or converted the property since the sum insured was last set.

Does my mortgage lender check my buildings insurance rebuild figure?

Lenders require you to hold buildings insurance from exchange of contracts and confirm cover is in place, but in practice most don't independently verify that the sum insured matches the true rebuild cost. That check is left entirely to you. A lender's interest is protected either way, since a mortgage clause typically means any payout goes toward the outstanding loan first, but a shortfall from underinsurance still falls on you as the homeowner if the payout doesn't stretch to a full rebuild. Don't treat "the lender was happy with it" as confirmation the figure is right. Run the free BCIS-based calculator yourself in your first month of ownership rather than assuming someone else has already checked it for you.

What's the difference between market value and rebuild cost for home insurance?

Market value is what a buyer would pay for your home, including the land it sits on and local demand. Rebuild cost, sometimes called reinstatement cost, is what it would cost a builder to reconstruct the physical structure from scratch, including materials, labour, site clearance, professional fees and VAT, but excluding the land, since the ground itself doesn't need rebuilding after a fire or flood. In expensive areas such as inner London, market value usually runs well above rebuild cost, and insuring for the full purchase price wastes money on cover you don't need. Elsewhere, particularly on older or larger properties, rebuild cost can sit close to or above market value. Always insure to the rebuild figure, never the purchase price or the estate agent's valuation.

Does buildings insurance sum insured go up automatically to keep pace with rebuild costs?

Some policies apply automatic index-linking at renewal, typically tracking a construction cost index, but not all do, and the uplift applied doesn't always match the real annual movement in the ABI/BCIS House Rebuilding Cost Index, which rose 3.9% in the year to July 2026. Never assume index-linking is switched on just because the insurer has not mentioned otherwise. Check your renewal documents each year for the specific percentage applied, and treat automatic index-linking as a partial safety net rather than a substitute for recalculating the figure properly every few years, particularly after any extension, loft conversion or other work that changes the floor area.

A £20,000 claim, £15,000 paid: the average clause explained

You signed the paperwork, picked up the keys, and ticked "buildings insurance sorted" off your list the day your solicitor confirmed cover was live from exchange. Job done, or so it feels. But at no point in that process did anyone actually work out what it would cost to rebuild your specific home from scratch, and the sum insured sitting on your policy right now is almost certainly a guess rather than a calculation.

That guess matters more than it used to. The ABI/BCIS House Rebuilding Cost Index, the official measure insurers use to track reinstatement costs, rose 3.9% in the year to July 2026 (ABI/BCIS House Rebuilding Cost Index, published 4 August 2026), and it moves most months without you ever touching the figure on your policy. If a serious claim lands and that sum insured has drifted too far behind reality, your policy's "average clause" doesn't just decline the shortfall: it cuts every payout by the same percentage you're underinsured, even on a partial claim that comes nowhere near a total loss.

Why your sum insured is probably a guess, not a number

Most new homeowners never calculate a rebuild figure at all. Comparison sites default to a generic estimate based on bedroom count and postcode, some buyers simply insure for the purchase price on the assumption that bigger is safer, and once the policy is set up it tends to sit untouched for years. A 2022-23 survey of properties inspected by loss adjusters Barrett Corp and Harrington found three in four were underinsured against their true rebuild cost, and BCIS itself has flagged this year that rising claims from drought, subsidence and flooding are increasingly the moment that gap gets discovered (BCIS, published 4 August 2026).

The confusion usually comes from mixing up two different figures. Market value is what a buyer would pay for your home, land included. Rebuild cost is what it would cost a builder to reconstruct the structure from scratch, excluding the land, since the ground doesn't need rebuilding after a fire. In expensive areas the two can be miles apart, and insuring to the purchase price in somewhere like inner London wastes money on cover you don't need. Get this backwards on an ordinary house, though, and you're the one exposed. So if you set your sum insured by copying the price on your mortgage offer rather than by calculating what a rebuild would actually cost, you're very likely carrying a gap you have not noticed yet.

What it actually costs to rebuild a typical home in 2026

Using BCIS-derived rebuild cost bandings that brokers use to guide sum insured figures, a semi-detached home costs roughly £1,800 to £2,200 per square metre to rebuild in 2026, rising to £1,900-£2,400 per square metre for a detached house, before any regional uplift is applied. Take a typical three-bedroom semi at around 90 square metres: at the £2,000 midpoint, the bare construction cost comes to £180,000. Insurers and BCIS both note that a full reinstatement figure needs to add site clearance and demolition, professional fees, and VAT on labour, which together typically add another 10-15% on top of the bare build cost. That pushes the realistic full reinstatement figure to around £200,000, not £180,000.

Two things push that number higher still. Regional uplift adds significantly in the most expensive areas: inner London typically adds 30-45% on top of the national bandings, and listed or non-standard properties add a further 30-50% for specialist materials and consent costs. Neither of those uplifts is optional if they apply to your home, and neither shows up if you have simply guessed at a round number. As covered in our new homeowner checklist, this is exactly the kind of figure worth getting right in your first month rather than assuming your solicitor or comparison site already checked it. So if your home falls into either category and your sum insured was set by a generic online quote, the gap between what you're insured for and what a genuine rebuild would cost is probably larger than you think.

The average clause: how a shortfall shrinks every claim, not just a total loss

This is the part most homeowners never learn until they need it. If your sum insured is below the true rebuild cost, your policy's average clause reduces every payout by the same percentage as the shortfall, not just on a total loss, but on any claim at all. Say your true reinstatement cost is £200,000, calculated as above, but your policy has sat at £150,000 since a comparison site set it years ago. That's 75% of the real figure. The Association of British Insurers recorded an average subsidence claim of £20,000 in the second quarter of 2026, a record high (ABI, Q2 2026, published August 2026). Under the average clause, a claim like that would pay out at 75%, or £15,000, leaving a £5,000 shortfall right at the point you need the money most.

It gets worse for smaller, more common claims. The ABI's average claim for storm, flood and burst-pipe damage rose 12% year-on-year to £8,548 in the same quarter (ABI, Q2 2026, published August 2026). At the same 75% cover level, that claim pays out £6,411 rather than the full amount, a £2,137 gap on a repair bill most households would struggle to absorb unplanned. This isn't a rare edge case reserved for catastrophic fires: it applies to the burst pipe or the cracked wall that every homeowner eventually deals with. So if you have never checked your rebuild figure against a real calculation, assume you're carrying this reduction on every claim you might ever make, not just the worst-case scenario you hope never happens.

When to check the figure, and what it costs to get it right

BCIS itself recommends checking the rebuilding cost figure properly at least every five years rather than relying purely on index-linking between renewals, and there are four points in the homeownership timeline where it's worth doing so. In your first month, run the free ABI/BCIS calculator at abi.bcis.co.uk, which takes about ten minutes and uses the same underlying data insurers rely on, rather than assuming the figure already on your policy is correct. At every renewal, check the specific percentage your insurer has applied for index-linking; not all insurers apply one automatically, and even where they do, it won't always match the real 3.9% annual movement in rebuild costs. After any extension, loft conversion or major structural work, recalculate immediately, since added floor area changes the rebuild figure directly, in the same way it changes the numbers in our home improvement guide. And at minimum every five years, treat a full reassessment as standard admin, in the same spirit as the seasonal jobs in our maintenance calendar or the cover-versus-cost maths in our piece on whether boiler cover is worth paying for.

None of this costs anything beyond ten minutes of your time for the free calculator, and updating your sum insured with your existing insurer rarely changes your premium by much unless the gap is large. So if it has been more than a year since anyone checked your figure, or you have never checked it at all, this is one of the cheapest pieces of financial admin available to a new homeowner, and it's worth doing before your next renewal rather than after a claim forces the issue.

The maths, in one place:

Typical three-bed semi, 90 sq m, at the £2,000/sq m BCIS midpoint: £180,000 bare build cost. Add site clearance, professional fees and VAT (10-15%): approximately £200,000 full reinstatement cost. If your sum insured has sat at £150,000, that's 75% of true cost. A £20,000 subsidence claim (ABI average, Q2 2026) then pays out £15,000, a £5,000 shortfall. An £8,548 storm/flood/burst-pipe claim (ABI average, Q2 2026) pays out £6,411, a £2,137 shortfall. Source: ABI/BCIS House Rebuilding Cost Index and Association of British Insurers, both published August 2026.

What this means for you

The maths points toward a simple action: check your rebuild figure this month, not at your next renewal. Most people who run this calculation properly for the first time find their sum insured is set by guesswork rather than by any real number, and the cost of finding out is ten minutes on a free calculator against a potential five-figure shortfall on the one claim you actually hope never to make. If you have extended, converted or renovated since you bought, treat that recalculation as urgent rather than optional, since added floor area is the single biggest driver of an outdated figure. And if your policy has sat untouched since the day you moved in, assume it's wrong until you have checked it, because on the evidence of the average subsidence claim alone, being wrong now costs considerably more than it did five years ago.