The Welsh Government has launched a public consultation on proposed changes to Building Regulations Part L (Conservation of Fuel and Power), alongside updates to Part F (Ventilation) and Part O (Overheating). The consultation, which runs until 17 November 2025, represents a major step forward in aligning Wales’ building standards with the country’s climate and net-zero commitments.
Key Proposals for New Homes
- Zero Carbon Ready Standard: New dwellings will need to be designed to achieve zero carbon emissions as the electricity grid decarbonises.
- Ventilation Options: Two compliance routes are under consideration — one based on DMEV (Decentralised Mechanical Extract Ventilation), and another on MVHR (Mechanical Ventilation with Heat Recovery), which delivers stronger energy savings but at higher upfront cost.
- Updated Metrics: The consultation proposes replacing the current Dwelling Energy Efficiency Rate with a new Energy Use Intensity (EUI) measure, which captures both regulated and unregulated energy use and recognises the contribution of onsite renewables.
- Renewables Requirement: All new homes will be expected to include a minimum level of onsite renewable generation.
- Weather Data: Cardiff will become the standard reference location for weather data, improving the accuracy of system sizing, particularly for heat pumps.
Ventilation and Commissioning
Part F is also set for important updates:
- Ventilation systems will need to be commissioned by either a competent person scheme member or the Building Control Body.
- Commissioning tests must use powered flow hoods, with rotating vane anemometers no longer accepted.
Existing Buildings and Overheating Risks
- For larger extensions (over 30 m²), developers will be required to integrate renewable energy solutions such as solar PV or solar hot water.
- Overheating measures will apply in two high-risk scenarios: window replacements in highly glazed flats, and loft conversions that introduce new glazing.
Methodology and Compliance Tools
The consultation outlines a move towards a new Home Energy Model (HEM), tailored to Welsh regulations, as a replacement for SAP. Should HEM not be fully ready by implementation, SAP will remain as a fallback option.
Non-Domestic Buildings
The proposals also aim to raise standards for commercial and public buildings by:
- Prioritising low-carbon heating solutions, including heat pumps and renewable-electric systems.
- Introducing a requirement for photographic evidence of insulation and services to support compliance checks.
- Updating the NCM and cSBEM methodologies, with draft versions now available for review.
This consultation signals a decisive shift towards more ambitious performance standards in Wales, with stronger emphasis on renewables, ventilation quality, and low-carbon heating. It provides a clear opportunity for stakeholders to influence the future of building regulations and help shape the transition to a net-zero built environment.