A review of fire safety issues arising from large-scale energy efficiency retrofits under PAS 2035. Are a new generation of cladding and insulation risks being created?. Retrofit Insulation Risks: A Review of PAS 2035 Implementation The UK's ambitious drive to decarbonise its housing stock, largely spearheaded by the PAS 2035 framework for energy efficiency retrofits, is inadvertently raising a critical question for fire safety professionals: are we, in our haste to insulate, creating a new generation of cladding and insulation risks reminiscent of the Grenfell tragedy? While PAS 2035 aims to ensure quality and safety in retrofit projects, a closer examination reveals potential vulnerabilities, particularly concerning the fire performance of insulation materials and their installation, which demand urgent attention from regulators, industry, and practitioners alike. Background The imperative to improve the energy efficiency of UK homes is undeniable. With an estimated 19 million homes requiring significant energy upgrades to meet net zero targets, the scale of the retrofit challenge is colossal. PAS 2035, developed by the British Standards Institution (BSI) and adopted as the overarching framework for domestic retrofits, seeks to provide a robust methodology, from initial assessment to post completion evaluation. Its core aim is to ensure that retrofit projects are designed and delivered to high standards, avoiding unintended consequences such as damp, mould, and structural issues. However, the framework's primary focus has historically been on energy performance and building physics, with fire safety considerations, while present, arguably not receiving the same level of granular scrutiny as other aspects. The shadow of Grenfell Tower looms large over any discussion of building materials and fire safety. The tragedy highlighted catastrophic failures in the specification, installation, and regulatory oversight of external wall systems (EWS), particularly concerning combustible insulation and cladding. The subsequent Hackitt Review and the Building Safety Act 2022 (BSA 2022) have fundamentally reshaped the UK's building safety landscape, placing a much greater emphasis on accountability, competence, and a "golden thread" of information. While the BSA 2022 primarily targets higher risk buildings (HRBs), the principles of robust fire safety design and competent installation are universally applicable, especially as millions of existing homes undergo significant material changes through retrofit. A key concern is the widespread use of various insulation materials, including expanded polystyrene (EPS), phenolic foam, mineral wool, and wood fibre, each with different fire performance characteristics. While mineral wool is non combustible, EPS and phenolic foams are combustible, albeit often treated with fire retardants. The manner in which these materials are integrated into existing building fabric, particularly in external wall insulation (EWI) systems, is critical. Poor installation, inadequate fire breaks, or a lack of understanding of material interactions can compromise the fire integrity of a building, potentially creating pathways for fire spread. Key Developments Recent years have seen a significant ramp up in retrofit activity, driven by government incentives and the urgent need to address fuel poverty and climate change. This surge has, however, coincided with a growing unease among fire safety professionals about the adequacy of fire risk assessments within the PAS 2035 process, particularly for non HRBs. One significant development is the increasing scrutiny of EWS on existing buildings, driven by the EWS1 form process and the broader implications of the BSA 2022. While EWS1 primarily addresses HRBs, the underlying concerns about combustible materials and fire spread are relevant to all buildings undergoing EWI. The industry has seen a proliferation of EWI systems, often applied to older, traditionally constructed buildings, where the interaction between new and old materials, and the detailing around openings and interfaces, can be complex and challenging to get right. The Health and Safety Executive (HSE), now the Building Safety Regulator (BSR), is taking a more proactive role in overseeing building safety across the lifecycle of buildings. While their initial focus is on HRBs, the principles of competence, robust design, and effective risk management will inevitably cascade down to other building types. The BSR's Gateway 2 and 3 processes for HRBs demand rigorous demonstration of fire safety compliance before construction and occupation, setting a precedent for the level of detail and assurance expected. Furthermore, the publication of PAS 9980:2022, "Fire risk appraisal of external wall construction and cladding of existing blocks of flats – Code of practice," provides a much needed framework for assessing the fire risk of EWS. While primarily aimed at blocks of flats, its methodologies and prin