Mass timber is revolutionising construction, but fire safety concerns remain. Understanding charring behaviour, delamination risks, and encapsulation strategies is essential.. The Mass Timber Revolution Cross Laminated Timber (CLT), Glulam, and other engineered timber products are increasingly used for multi storey construction, including buildings up to 18 storeys. Fire safety is the critical enabling factor. How Timber Performs in Fire Charring behaviour: Timber burns at a predictable rate: 0.65 mm/min for softwood (BS EN 1995 1 2) The char layer insulates the remaining timber, slowing the charring rate Residual section retains full structural strength Predictable performance enables structural fire engineering calculations Delamination risk (CLT specific): When the char layer reaches an adhesive line between CLT layers, the char can fall away This exposes uncharred timber to direct flame — accelerating the burning rate Adhesive type is critical : polyurethane (PUR) adhesives perform better than melamine (MUF) BS EN 16351 now includes adhesive bond strength retention requirements at elevated temperatures Regulation 7 and Height Limits England: Above 18m: Regulation 7 effectively prohibits combustible materials in external walls This includes structural CLT in external wall zones Internal CLT structure permitted at any height (not covered by Regulation 7) Below 18m: CLT permitted with appropriate fire engineering International comparison: Austria, Canada : CLT buildings up to 18 storeys built and occupied USA : IBC 2021 allows mass timber up to 18 storeys with sprinklers Japan : 70m timber hybrid buildings in development Encapsulation Strategy Full encapsulation: All CLT surfaces covered with non combustible board (typically 2 layers of plasterboard) Provides 60 120 minutes fire resistance before timber is exposed Eliminates contribution of CLT to fire load during design fire Preferred approach for buildings above 4 storeys Partial encapsulation: Some CLT surfaces left exposed for aesthetic reasons Exposed timber contributes to fire load — must be accounted for in fire engineering Additional suppression (sprinklers) typically required as compensatory measure Detailed fire engineering analysis required Fire Testing and Research Significant research programmes ongoing: BRE full scale CLT compartment fire tests (2019 2024) NFPA/APA tall wood building fire tests European COST Action FP1404 timber fire research Edinburgh University CLT fire research programme For mass timber fire engineering, contact us. Magnus Opifex SEVEN LTD — UK's Leading Fire Safety & Fire Engineering Consultancy 🌐 magnus opifex.co.uk 📞 +44 7486 691724 ✉️ office@magnus opifex.co.uk Founders: Nicoleta Vasile, Baroness of Brattleby — CEO, Lawyer and Barrister, Legal & Administrative Director Alina — Technical Director & Expert Fire Engineer (BEng) Head Office: Ealing Cross, 85 Uxbridge Road, London W5 5BW Magnus Opifex SEVEN LTD delivers engineering led fire engineering, fire risk assessments, CFD modelling, and building safety consultancy across the United Kingdom and internationally. With over 20 years of combined experience and a UK portfolio spanning healthcare, residential and infrastructure, we bring truly engineered solutions with a personal touch. © 2026 Magnus Opifex SEVEN LTD. All rights reserved.