Green premium — energy-efficient price premium

HM Land Registry Price Paid Data (arm's-length residential sales, category A, excluding new builds), five-year window, refreshed monthly.

MHCLG Energy Performance of Buildings Register: current energy rating, total floor area, construction age band. Bulk mirror vintage is stated on /data.

Each sale is matched to its most recent EPC (lodged up to 10 years before or 6 months after the sale) on a normalised address key within the postcode, giving a £/m² figure per sale.

Within each outcode and property group (house/flat), sales are stratified by construction-era band. Within each band with at least 5 sales on each side, the median £/m² of A–C homes is compared with D–G homes.

The published premium is the sample-weighted mean of those within-band differences. We publish BOTH the age-adjusted figure and the naive (unadjusted) gap; an outcode is displayed only when both sides have n ≥ 20.

Energy-efficient homes are disproportionately newer, and newer homes command different prices for reasons unrelated to energy. In several outcodes the naive gap reverses sign once construction age is controlled (e.g. a validation case where +9.6% naive became −2.7% adjusted). Publishing both figures makes the adjustment auditable.

EPC lodgement is selective: recently lodged homes skew renovated/recently transacted.

The rating can predate a retrofit or postdate the sale's true state (lodgement window).

Stratification is by age band only; within-outcode street effects can still confound.

Confidence intervals are on the roadmap; treat small-sample outcodes with care (sample sizes are published).