Government announces full review of Overheating Regulations following industry feedback

The government has confirmed that it will launch a full review of Approved Document O, the overheating regulation first introduced in 2021 to limit excessive heat in new homes. The decision follows extensive industry feedback gathered through the Future Homes Standard consultation, undertaken in 2023, with the consultation response published on 24 March 2026.

Updated versions of Parts L and F were published on the same date; however, Part O will now undergo its own standalone review process, reflecting the significant volume and complexity of issues raised by stakeholders and placing it on a separate trajectory from the rest of the Future Homes Standard updates.

In this article we’ll take a look at some of the feedback provided in the consultation responses and announced plans by Government.

Questioning the Simplified Approach

Across the industry, feedback on Part O’s simplified method highlighted concerns around complexity, clarity and potential limitations in its application. Builders and assessors highlighted numerous omissions, including thermal mass, internal shading, passive design strategies, and triple glazing.

As a result of these gaps, many organisations are bypassing the simplified approach entirely and moving straight to dynamic thermal modelling (DTM). Several respondents reported that developments which fail the simplified method frequently pass DTM without any design changes,

Before Part O was introduced, mitigating overheating risk was contained in Part L and determined within the SAP assessment. A growing number of stakeholders therefore questioned why overheating assessment is no longer integrated into SAP, or whether it could instead be brought into the upcoming Home Energy Model (HEM) to improve consistency and reduce duplication of work.

Part O vs Other Building Regulations

One of the strongest recurring themes was the conflict between Part O and other areas of the Building Regulations – particularly Parts F (Ventilation), L (Conservation of Fuel and Power), Q (Security), B (Fire Safety) and K (Protection from Falling, Collision & Impact).

Security requirements were repeatedly cited as a major challenge, with many ground floor bedrooms unable to satisfy both the ventilation requirements of Part O and the security requirements of Part Q.

Respondents also highlighted that noise constraints often prevent residents from opening windows at night, pushing developments toward mechanical cooling systems. This reliance on active cooling contradicts the original intent of Part O and sits uncomfortably alongside the energy efficiency objectives of Part L.

Concerns were also raised around window‑sill height requirements, where Part O has resulted in sill heights exceeding those required under Part K. Respondents noted that this can compromise accessibility, restrict views for wheelchair users, and result in uniform, less aesthetically appealing façades.

Expansion of Overheating Requirements

Respondents widely identified extensions, conservatories and highly glazed additions as a significant overheating risk, particularly where large bifold doors or multiple rooflights are installed. The overwhelming view was that clearer guidance is needed on glazing specification, thermal separation, and shading solutions in these scenarios.

Competency and Consistency is Key 🔑

Widespread inconsistencies in assessment quality, reporting standards and modelling outcomes led many respondents to call for stronger requirements around recognised competency, as well as formal approval of software and assessment tools to ensure consistent results. There was also a strong push for standardised reporting formats and greater transparency in the assumptions used within overheating models.

Elmhurst fully supports this feedback and is already taking proactive steps to raise standards across the industry. Our Overheating Scheme provides formal recognition for qualified DTM assessors, supported by a standardised NHBC approved reporting template, for more information on our training and scheme please visit our website:

Government Response

In its official response, the government announced plans for a full technical review of Part O, including:

• Adoption of the updated CIBSE TM59 for dynamic modelling
• Improvements to the simplified method
• Review of noise and security guidance
• Consideration of expanding Part O to material change of use dwellings
• Analysis of conflicts with other parts of the Building Regulations
• Updated weather files reflecting future climate scenarios

Some changes are already emerging, for example, where air conditioning and/or reduced g‑values are required to comply with Part O, the Part L energy efficiency standards will also account for these to prevent conflicts between the two.

Final Thoughts

The outcomes of the call for evidence align closely with the feedback and queries received by our New Build Dwellings Support team since Part O’s introduction. We therefore welcome and fully support the government’s decision to conduct a comprehensive review.

Elmhurst firmly believes that retaining a dedicated overheating regulation is essential to ensuring that UK homes remain safe, resilient and comfortable, both now and in the future. We strongly support the need for competency, standardisation, and clarity and hope that any future revisions will make assessments more straightforward for assessors and modellers, while improving understanding across the wider industry.