New Part L for Wales (Targets and Notional)
As if we didn’t already have enough excitement unpacking the Future Homes Standard for new building sites in England, the Welsh Government has now released its own version.
This revised Approved Document Part L will apply to any building work where the relevant building inspector accepts applications from 4th March 2027.
Any unstarted buildings on existing sites after 4th March 2028 will need to meet the new regs, regardless of when the site was submitted.
⏰ These dates kick in a full three weeks before FHS goes live in England.
As with the current Part L, most of the English (UK) and Welsh versions are identical, but there are a few curveballs developers need to be aware of.
🎯 Targets:
The U-Value backstops are not changing. It’s worth noting these are already much stricter than the U-Value targets used in England. This is because England uses the Fabric Energy Efficiency (TFEE) for design flexibility whereas Wales doesn’t.
🟢 The mandatory Energy Performance Certificate target is going. Currently in Wales, all new dwellings must achieve a B rated EPC. But with EPC Reform on its way, it would easily get messy navigating the regs if that target remained in place.
⚡ To replace it, we have a new, mandatory Energy Use Intensity target. This is defined as the ‘maximum energy use of the building’.
Depending on which guidance you read, EUI targets can include unregulated energy (which SAP isn’t great at calculating) and sometimes ignores energy from PV. We’re waiting on precise definitions about the Part L calculation.
🎯 Alongside the EUI target, we’ll continue to use the Target Emission Rate and Primary Energy Rate. All three need to pass for the dwelling to be compliant with SAP. (As with England, Wales is moving to SAP10.3, but will swap to the Home Energy Model in the not-too distant future).
🏠 Notional Specification
This is used to calculate the targets. The actual house is compared to a predefined specification to check it performs better.
♨️ The Notional heating system swaps from a gas boiler to an Air Source Heat Pump. This spells the end for fossil fuel heating systems in new homes. To pass SAP10.3, heat pumps will be required in the vast majority of buildings.
☀️ The g-value of windows has been unlinked from the Notional. Under current regs, SAP encourages a high g-value, as a naturally lit home uses less energy. But Part O (Overheating) requires low g-values to reduce the risk of excessive internal temps.
This change means overheating compliance takes precedent over energy performance. SAP won't penalise a house that needs low g-values.
⚖️ Also in the notional, the glazing U-Value is lowered from 1.3 to 1.2, the air test is lowered from 5 to 4, and the ventilation is based on dMEV instead of extraction fans.
It's still possible to pass with higher air test scores and other ventilation systems, as long as everything balances overall.
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