Two different numbers
Insurance rebuild cost: the cost of rebuilding a like-for-like replacement after total loss, excluding land, using the BCIS/ABI Rebuild Cost calculator[ABI/BCIS]. Typically £1,200-£1,800/sqm for a standard UK property. Construction rebuild cost (voluntary KDR): the cost of demolishing and building a new, often larger, often higher-specification dwelling. Typically £2,000-£3,500/sqm in mid-range tier plus all the statutory and ancillary lines on this site.
Why the gap
The insurance figure assumes the existing footprint, the existing fabric standard, no design upgrade, no betterment, no land cost, no temporary accommodation, no statutory fee uplift. KDR is the opposite case on every line: usually larger, usually better-specced, full Future Homes Standard envelope.
When to commission a formal RICS reinstatement assessment
Listed buildings; non-standard construction (timber-frame, ICF, large-format precast); architect-designed with bespoke joinery and finishes; properties valued above £1.5M. RICS reinstatement assessments cost £450-£950 and protect against under-insurance penalties.
Updating cover after a KDR
The new dwelling has a new and usually higher reinstatement cost. Notify the insurer at completion. Most insurers will re-rate the policy from completion certificate date; failure to do so leaves you exposed if the new dwelling burns and the schedule still quotes the old reinstatement figure.