The UK construction sector has navigated a strict regulatory landscape for timber high-rise projects since the 2018 ban on combustible materials in buildings above 18 metres. Cross-laminated timber (CLT), once positioned as a fast and sustainable alternative to concrete and steel, now faces the question: can it return to UK high-rise construction under new Building Safety Regulator (BSR) guidance?
The ban and its immediate impact
Following the Grenfell Tower fire in June 2017, the government introduced Approved Document B in December 2018, prohibiting the use of combustible materials—including CLT and other engineered timber systems—in the external walls of residential buildings taller than 18 metres. The measure effectively halted a growing pipeline of CLT high-rise projects, particularly in the residential sector where speed of assembly and reduced site logistics had made the material attractive.
The ban did not prevent timber use entirely. Internal structural frames, floors, and cores remained permissible if encapsulated in non-combustible materials meeting fire-resistance standards. Yet the additional cost and complexity of encapsulation eroded much of CLT's competitive advantage, particularly against traditional concrete floor slabs.
Building Safety Regulator's role and new guidance
The Building Safety Regulator, operating under the Health and Safety Executive (HSE), now provides dedicated guidance on the design and construction of higher-risk buildings via a separate GOV.UK portal. The BSR's remit covers buildings above 18 metres or with seven or more storeys that contain at least two residential units. This includes new-build and refurbishment projects where fire safety, structural integrity, and material choice are subject to stricter scrutiny.
Recent BSR guidance clarifies performance expectations for timber structures. While combustible materials remain banned in external walls of higher-risk buildings, internal use of CLT is acceptable where designers can demonstrate compliance with functional fire-safety requirements. This includes robust compartmentation, adequate means of escape, and fire-resistance ratings validated through testing or engineering analysis.
Embodied carbon and the net zero imperative
The push to reconsider CLT in high-rise stems partly from carbon reduction targets. Embodied carbon from construction and refurbishment currently accounts for 20 per cent of UK built environment emissions, according to the UK Green Building Council (UKGBC). Concrete and steel production dominate this share. UKGBC is undertaking feasibility studies into the design, delivery, and cost of net zero carbon buildings, and timber remains one of the few structural materials that can deliver measurable embodied carbon savings at scale.
Designers face a trade-off: CLT reduces upfront carbon but introduces fire-safety complexity. Encapsulation with gypsum boards, intumescent coatings, or mineral cladding adds weight, cost, and embodied carbon back into the equation. For projects targeting sustainability certifications, the net carbon benefit must be calculated on a case-by-case basis.
Pilot projects and phased reintroduction
A small number of UK projects are testing the regulatory and commercial viability of timber high-rise under the new framework. These pilots focus on hybrid construction, combining CLT floors with concrete or steel cores, and rely on early engagement with building control and the BSR to agree fire-engineering strategies. Contractors including Skanska UK and Balfour Beatty have explored modular CLT systems for mid-rise residential schemes, though few have progressed beyond planning.
The route back to mass timber in UK high-rise is unlikely to mirror pre-Grenfell optimism. Instead, the sector expects a phased reintroduction anchored in rigorous fire testing, third-party certification, and transparent compliance documentation. The BSR's emphasis on the 'golden thread' of building information—continuous digital records of design intent, material specifications, and safety case—means that BIM workflows and data handover will be central to any CLT project seeking approval.
Implications for designers and specifiers
For architects and structural engineers, the practical consequence is longer lead times and higher upfront engineering costs. Fire consultants must be involved from concept stage, and performance-based design—rather than prescriptive compliance—becomes the norm. This shifts risk and requires clients willing to accept additional design fees and programme uncertainty.
Material suppliers, meanwhile, face pressure to provide comprehensive fire-test data and third-party certification for CLT panel systems, adhesives, and assembly details. The absence of a standardised UK testing protocol for mass timber assemblies remains a barrier. European test data may not satisfy BSR or building control requirements, and bespoke UK testing is expensive and time-consuming.
Outlook
Cross-laminated timber will not disappear from UK construction, but its role in high-rise remains constrained by regulation and commercial caution. The path forward depends on continued dialogue between the BSR, industry bodies, and project teams willing to invest in demonstrating compliance. For now, CLT's strongest case lies in buildings just below the 18-metre threshold, and in hybrid systems where timber's embodied carbon benefits can be realised without triggering the most stringent fire-safety requirements.
The broader question—whether the UK will adopt a risk-based approach to timber high-rise similar to those in Austria, Norway, or Canada—remains unanswered. Until then, designers must navigate a framework that prioritises safety over speed, and treats mass timber as the exception rather than the rule.
