More than half of homes in England and Wales have an energy performance certificate (EPC) rating of ‘D’ or below, according to analysis by Emperor Paint.
The data revealed that 55% of properties fall into bands D to G, indicating average to very poor energy efficiency, with implications for future regulatory requirements and retrofit demand.
The Isles of Scilly recorded the highest proportion of lower-rated homes, with 85% of properties rated ‘D’ or below.
Gwynedd (74.3%) and Pendle (74.1%) were the next most affected areas, based on analysis of government EPC data covering January 2008 to February 2026.
The findings come as EPC regulations are set to change, with new metrics including fabric performance, heating systems, smart readiness and energy cost due to be introduced, and expected to become mandatory from October 2029.
Minimum standards for rental properties are also set to tighten, with an equivalent EPC rating of ‘C’ required from October 2030.
Jack Reading of Emperor Paint said: “Changes to energy performance certificates mean that they will now be based on how properties retain heat, rather than how much energy a property uses.
“The vast majority of exterior walled surfaces are porous, meaning that they can become saturated with water.
“Research suggests damp content of 5% can lower the insulating properties of a surface by as much as 50%.
“This means that when the exterior walls of homes become saturated with water, it can lead to an increase in heat loss.”
Reading added: “To improve the thermal performance of your home’s exterior walls, you will need to reduce the amount of heat your home loses as a result of wet exterior walls.
“Using super hydrophobic masonry paint can help you to achieve this as it reduces water absorption, while high breathability ensures no moisture can build up within the wall.
“As weather conditions become more extreme, with warmer summers and wetter winters, exterior wall coatings not being included in EPC ratings, under ‘Fabric Performance’, represents a growing gap in how home energy efficiency is measured in the UK.
“Without accounting for how walls perform in real, weather-exposed conditions, EPC scores risk overlooking a key factor influencing heat loss.
“As climate pressures intensify, this gap is only set to widen, meaning properties could appear more energy efficient on paper than they are in practice, an issue that is particularly significant given the UK’s ageing housing stock.”