Hot nights, planning constraints and housing by postcode district — Great Britain (2026-09-v1)

2,863 postcode districts of Great Britain (England 2,210, Scotland 453, Wales 200). For each district: nights in June–August 2025 and 2026 whose minimum 2 m temperature stayed at or above 18 °C and 20 °C, against the 1991–2020 normal (ERA5, nearest 0.25° cell with land fraction ≥ 0.5); share of live postcodes inside conservation areas (England: planning.data.gov.uk; Scotland: Historic Environment Scotland; Wales: Welsh Government), Article 4 areas and listed-building points (England); and the Census housing and heating mix (2021 England and Wales, 2022 Scotland). Built for coolingindex.co.uk, which uses these layers to answer whether a home is likely to overheat and what can be fitted without planning permission. Method, column definitions and required attributions: README.md and dictionary.csv. Northern Ireland is not included (its postcode data needs a separate licence from Land and Property Services).