Results from new fire testing, published by Willmott Dixon last week, have closed a critical technical gap in Cross-Laminated Timber (CLT) construction by delivering certified, repeatable cavity-barrier details that eliminate the need for project-specific fire assessments. Conducted in collaboration with passive fire-protection specialist Siderise and KLH, the testing validates cavity-barrier solutions for wall, floor, and rainscreen interfaces, tackling a recurring source of delay and regulatory uncertainty that has constrained CLT projects across the industry.
It comes as testing at Siderise’s Innovation Centre in Maesteg, Wales, targeted three interface scenarios identified by industry specialists as the highest risk for concealed‑space fire spread: 1) vertical CLT wall interfaces with the EW‑CB 30 cavity barrier (EN1366‑4); 2) horizontal floor‑to‑wall interfaces with EW‑CB 30 (EN1366‑4); and 3) horizontal floor‑to‑wall rainscreen interfaces with RH25 90/30 (TGD19 prEN1364‑6). All three configurations met the required performance criteria, including worst-case trials on 100mm five-layer CLT panels to the relevant European standards.
Until now, the absence of standardised, validated cavity-barrier details has forced design teams to commission bespoke assessments, inflating costs, extending programs, and increasing regulatory risk. The published test evidence provides architects, engineers, and contractors with repeatable, certified details they can specify with confidence, which is expected to shorten procurement timelines and reduce approval friction for CLT projects.
“This testing addresses a genuine technical gap that affects every organisation working with CLT,” said Jessica Winyard, architectural technologist at Willmott Dixon. “By working collaboratively with Siderise and KLH to develop these solutions, we’re helping to accelerate the adoption of low‑carbon construction methods while ensuring robust fire‑safety performance.”
Siderise said the programme validated its EW-CB and RH25 cavity-barrier products across multiple CLT configurations, demonstrating their capacity to prevent fire spread through concealed spaces—a core safety requirement for timber structures. Chris Mort, Director of Testing & Project Engineering at Siderise, noted the Innovation Centre was established to generate the empirical data the industry needs to translate novel structural systems into compliant building practice and said the collaboration produced repeatable “standard details” suitable for specification.
The practical consequence extends beyond individual projects. CLT is prized for its embodied carbon advantages over conventional materials, but uncertainty about concealed-space fire protection has repeatedly impeded procurement and design decisions. By producing certified solutions for common interfaces, the programme removes a discrete technical obstacle to wider CLT deployment and gives building control officers and project teams a common technical reference for assessing compliance.
Please note: Willmott Dixon, Siderise, and KLH have confirmed that full test reports and certification documents will be published to support specification and compliance checks on the Willmott Dixon website.
