The UK's net-zero push is driving mass retrofit insulation programmes. We examine the fire safety implications and how to avoid creating new risks while improving energy performance.. The Net Zero Imperative vs Fire Safety The UK Government's commitment to achieving net zero carbon emissions by 2050, combined with the Energy Performance Certificate (EPC) requirements for rental properties, is driving an unprecedented wave of building retrofit activity. Central to most retrofit programmes is the installation of additional insulation — particularly External Wall Insulation (EWI) systems. However, the post Grenfell regulatory environment has created a fundamental tension: the materials and methods used to improve a building's thermal performance can simultaneously compromise its fire safety. Navigating this tension requires careful engineering judgement and regulatory awareness. The Fire Risk Spectrum of Insulation Materials Not all insulation materials present the same fire risk. Understanding the spectrum is essential: Non Combustible (Euroclass A1/A2) Stone wool / mineral wool — The default choice for fire safe retrofit. Non combustible, excellent fire resistance Glass wool — Similar fire performance to stone wool, lighter weight Calcium silicate — Non combustible board insulation Limited Combustibility (Euroclass B) Phenolic foam — Chars rather than melts, relatively good fire performance Modified PIR — Enhanced fire performance polyisocyanurate Combustible (Euroclass C F) Expanded Polystyrene (EPS) — Widely used pre Grenfell, melts and burns readily Standard PIR/PUR — Polyisocyanurate/polyurethane, combustible but with some self extinguishing properties Wood fibre — Natural insulation, combustible but slow burning Regulatory Requirements for Retrofit Insulation Buildings Over 18m The ban on combustible materials (Regulation 7 of the Building Regulations) applies to: External wall insulation systems External cladding systems Specified attachments Only materials achieving Euroclass A1 or A2 s1,d0 are permitted Buildings 11 18m PAS 9980 assessment methodology applies: Risk based assessment of external wall construction May permit limited combustibility materials depending on other risk factors Fire engineering justification required Buildings Below 11m No blanket ban on combustible materials, but: Fire risk assessment must consider the insulation system Building Regulations still require adequate fire safety Insurance implications of material choices Common Retrofit Fire Safety Failures Our experience of assessing retrofit insulation projects reveals recurring issues: Cavity barriers omitted in EWI systems, creating continuous cavities for fire spread Fire stopping at openings (windows, doors, penetrations) not installed or inadequate Incompatible materials used together in the same system Party wall junctions not fire stopped, allowing fire spread between properties Ventilation conflicts — insulation blocking required ventilation paths for smoke control Access for firefighting compromised by increased wall thickness Missing fire rated fixings — standard fixings used instead of fire tested alternatives Best Practice for Fire Safe Retrofit A responsible retrofit programme should follow these principles: 1. Fire engineer involvement from concept stage — Not as an afterthought 2. Material selection based on building height and risk — Default to non combustible 3. System testing evidence — Insulation installed as part of a tested system, not ad hoc 4. Cavity barrier design — Detailed drawings showing all cavity barriers and fire stops 5. Independent inspection — Third party inspection of fire critical installation details 6. As built records — Detailed documentation for the building's 'golden thread' 7. Fire risk assessment update — Post completion reassessment of fire risk For retrofit fire safety engineering and assessment, contact Magnus Opifex.