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London’s Grenfell Tower fire in June 2017 resulted in the death of 72 people and the start of a debate about the changes to processes and building regulations required to ensure such a tragedy never happens again.

Jonathan Platt is Existing Buildings Lead at AES Sustainability, an award-winning team of energy and sustainability consultants based in the South-West of England but operating across the UK.

In this article Jonathan suggests ways the UK construction and property sectors can balance more stringent regulatory requirements with action to support long term performance.

Why fire safety and energy efficiency are both vital to building regulation enforcement? 

In the years following the Grenfell Tower tragedy, the UK construction and property sectors have undergone a profound transformation in building regulations compliance. Fire safety is now a dominant driver when it comes to the design and construction of new buildings – and rightly so. It is also just as important for refurbishment and the driving force behind many façade remediation, retrofit and recladding projects. Strengthened legislation and oversight placing resident safety at the forefront of decision‑making has been a legacy for the UK construction and property sectors

However, as the building industry mobilises to remove combustible materials and achieve compliance with fire safety regulatory requirements, there is a growing need to ensure that energy performance is not inadvertently deprioritised. Recladding schemes represent a rare and significant opportunity to improve both safety and sustainability outcomes. Realising this potential depends on embedding energy performance assessment into project plans and processes from the outset.

What is Part L of the UK’s building regulations code?

Part L of the UK’s building regulations governs the energy efficiency of buildings: from insultation for walls, roofs and floors to the amount of heat that escapes doors and windows. Energy modelling and Part L compliance should not be treated as secondary or reactive considerations within fire improvement led projects. Instead, they play a crucial role in ensuring that buildings perform effectively as holistic systems. The removal and replacement of cladding, insulation and associated elements, trigger requirements that all building contractors need to follow.

This means that any affected thermal elements must be assessed against current energy efficiency standards. This creates both a regulatory obligation and a strategic opportunity to enhance performance. Where approached correctly, recladding and retrofit works can deliver meaningful reductions in heat loss, improve airtightness and address long‑standing deficiencies in the building fabric.

However, achieving these outcomes is not always straightforward. Many high‑rise residential assets, for example, come with inherent constraints. These constraints include limited structural capacity, restricted façade depths and complex geometries. In addition, the need to prioritise non‑combustible materials in line with fire safety requirements can restrict design choices and complicate thermal optimisation. As a result, full compliance with current Part L standards is not always technically or financially feasible in every instance. This makes a robust, evidence‑based approach to energy assessment essential, enabling design teams to demonstrate that reasonable improvements have been made while maintaining the primacy of protecting residents.

Why early stage integration is critical for energy performance? 

A critical factor in achieving this balance is early‑stage integration. When energy performance is considered from the beginning of a recladding or retrofit project, alongside fire safety, design teams are better equipped to develop coordinated and efficient solutions. Early energy modelling allows different façade build‑ups, insulation strategies and material options to be tested before specifications are fixed. This provides the opportunity to:

• optimise U‑values.
  U-values indicate how much heat is lost through a specific thickness of material.

• identify and mitigate thermal bridging.
  This is a point in the walls, floors or roof where heat has an increased opportunity to escape to the outside or for cold to come in.

• ensure continuity of insulation and airtightness layers.
  Simply put, air tightness refers to the prevention of unwanted drafts that can occur in any building.

It also supports more effective coordination between disciplines, reducing the risk of conflicts or compromises emerging later in the design process.

The importance of this integrated approach is clearly demonstrated by the work of our energy and sustainability consultants on a high‑rise residential building in London. As part of a major fire safety remediation programme, AES Sustainability was appointed to provide Part L assessments and improvement recommendations to support approval by the Building Safety Regulator.

The project involved the removal of existing rainscreen and stone cladding systems, along with combustible insulation and timber elements.

These were to be replaced with non‑combustible alternatives including Rockpanel cladding, aluminium components and mineral wool insulation. These measures significantly enhanced the fire performance of the building, addressing critical safety risks.  

At the same time, changes to the building façade  triggered the need for a comprehensive energy assessment. The building had  multiple external wall types, each requiring detailed analysis to confirm compliance or identify opportunities for improvement.

Why building a strategy for a sustainable retrofit is important?

We carried out elemental U‑value calculations, assessed  condensation risk, and provided guidance on maintaining airtightness continuity and mitigating thermal bridging. Thanks to this work, a strategy to meet Part L requirements was achieved. This level of technical analysis ensured that the thermal performance of the  building refit was fully understood and optimised wherever practicable.

In cases where full compliance with Part L could not be achieved due to structural, dimensional, or design constraints, robust feasibility justifications were submitted in line with regulatory guidance. These demonstrated that the proposed solutions represented the best achievable outcome within the project’s parameters.

This ensured that improvements were delivered wherever possible without compromising fire safety objectives. The resulting Part L report formed a key component of the submission to the Building Safety Regulator, supporting the successful approval of the scheme and allowing works to proceed with a clear, agreed specification.

Why energy performance assessments are critical to building control?

This example highlights the critical role that energy performance assessments play, not only in achieving compliance, but in supporting effective decision‑making within complex, constraint‑driven projects. It also illustrates the importance of collaboration between clients, design teams and specialist consultants in navigating an increasingly rigorous regulatory environment.

As the Building Safety Regulator introduces greater scrutiny through the gateway approval process, the need for clear, evidence‑based submissions has become more important than ever. Beyond compliance, the integration of energy performance considerations into recladding works delivers significant long‑term benefits.

Improved thermal performance reduces energy demand, contributing to lower operational carbon emissions and supporting the UK’s broader net zero ambitions. For residents, this translates into improved comfort, reduced energy bills and healthier living environments, outcomes that are particularly important in high‑rise residential buildings. From an asset perspective, enhanced energy performance can improve ratings, reduce lifecycle costs, and strengthen overall value in a market increasingly shaped by Environmental, Social and Governance (ESG) considerations.

Why energy performance is key to Part L compliance?

Ultimately, the post‑Grenfell landscape demands a more holistic approach to building performance. While fire safety must remain the overriding priority, it should not be pursued in isolation. Recladding projects offer a unique opportunity to address multiple aspects of building performance in a single intervention. Failing to integrate energy considerations risks missing that opportunity for decades to come. By embedding energy modelling and Part L assessments from the outset, the industry can ensure that buildings are not only safer, but also more efficient, resilient, and sustainable. 

It is possible to demonstrates that this balance is both achievable and essential. Through early engagement, rigorous analysis and close collaboration, it is possible to deliver outcomes that satisfy UK building regulation requirements while enhancing long‑term performance. As the sector continues to respond to evolving regulations and increasing expectations, the integration of fire safety and energy performance will remain a defining challenge, and a critical opportunity, for the built environment.

AES Sustainability are a leading UK-based technical consultancy that can help with advice and technical support on every stage of your development project.  Visit our contact page to get in touch today.