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Under SAP, assessors simply enter a sheltered sides rating between zero and four to indicate how exposed a property is to the elements. While this provides a broad indication of site conditions, it lacks the detail needed to fully understand how a building interacts with its surroundings.

HEM introduces a far more detailed methodology. Assessors must now record the height, distance and orientation of surrounding obstacles, allowing the model to calculate their impact on both solar gains and wind exposure. This information is then combined with weather data to create a more realistic picture of operational energy performance.

The implications are considerable. Modelling by AES – a property with zero obstacles and one surrounded by skyscrapers - has demonstrated just how influential these new inputs can be. The heavily shaded house recorded an increased heat demand of 23%, mostly due to the reduction in solar gains. Total energy demand is 28% higher and, as you'd expect with a heavily shaded building, the performance of the PV drops considerably.

So, considering the two extremities, a dwelling that's free from obstructions will give better energy performance overall, but actual results will vary for each individual plot.

For developers and designers, this reinforces the importance of considering building orientation and surrounding structures early in the design process. Site constraints that may once have appeared relatively minor could become increasingly important as HEM influences compliance calculations and EPC ratings.

As HEM continues to evolve, it is becoming increasingly clear that understanding the relationship between buildings and their surroundings will be essential for achieving the best possible energy performance.

For further press information, please contact David Ing at Ing Marketing on david@ing.marketing or visit www.ing.marketing