U-values and insulation depth have long been the starting point for energy efficient walls – but has that all changed since the latest round of Building Regs updates?

Creating low-energy, low-carbon and low-bills homes is a critical consideration for self builders The legal framework for new dwellings’ energy performance is enshrined in Building Regs, with guidance on how to meet those regulations outlined in Approved Document L – Conservation of Fuel and Power. Part L was last updated in 2021, setting significantly stricter targets for CO2 emissions from new housing – areduction of 31% compared to the previous standard. In England, those changes came into force in June 2022 (taking effect in Wales from November 2022). Scotland has made similar – if slightly more rigorous – updates to its own Section 6 (energy) rules, effective from February 2023. For simplicity, in this article we’ll be largely focusing on the England & Wales updates. Given it typically takes a year or more to get from concept to starting on site, we’re only now beginning to see the impact on projects breaking ground. So, what do you need to know to ensure your new home meets the regs and achieves your energy goals?

SAP & the notional building

Every new build home in the UK has to be assessed against the regs at the technical design stage via a SAP calculation – and all three countries have now adopted the latest SAP10.2 specification to measure this.

Fundamentally, an energy assessor must measure your proposed design’s performance in SAP10.2 software to ensure it complies. “The regs work by creating a digital model of your new home and applying a predetermined set of performance figures to it,” explains Paul Newman, self build director at timber home specialist Potton. The baseline for comparison is set out in Approved Document L via what’s known as the notional building. “As long as what you intend is better overall than the notional building model, then you will meet the minimum regulatory requirement – provided all the individual fabric elements are better than a set of backstop values,” says Paul.