More and more projects could soon use cross‑laminated timber (CLT) in fully exposed outdoor environments, with researchers at the University of Auckland developing a suite of new durability systems that could change how mass timber is deployed across New Zealand.
That is according to Dr Gary Raftery, Research Director at the University’s Circular Innovations Research Centre, who oversees durability and performance research within the Structural Timber Innovation Laboratory, and is developing programmes that could open the door to outdoor applications of CLT, a material that is still largely limited to interior environments.
Raftery said that whilst CLT is known for its strength and versatility, unprotected exposure to the elements can lead to rot, mould, dimensional instability and structural compromise. “We want to ensure that solutions align with circular‑economy principles, so cross‑laminated timber elements can be reused, repurposed or recycled at the end of their service life. This data will give designers the confidence to adopt more sustainable construction practices and further support a transition to low‑carbon construction.”
Working with industry partners, Raftery’s team is assessing adhesive and preservative systems to improve CLT’s performance while keeping sustainability front‑of‑mind. At the same time, life‑cycle analysis on end‑of‑life pathways is underway, with early findings already informing design engineers and expected to contribute to future updates to building standards.
To push CLT into more demanding environments, the team is putting the material through some of the harshest conditions applied to CLT panels. Long‑term exposure trials, conducted across outdoor field sites and controlled laboratory simulations, are tracking how timber deteriorates and how its chemical structure changes under stress. At the same time, high‑powered microscopy and chemical‑fingerprinting tools are offering new insights into how CLT responds to moisture, UV radiation and biological attack, building a clearer picture of its performance in fully exposed settings.
CLT, made by stacking and gluing layers of timber boards together, has become a popular low‑carbon material for walls, floors and roofs. Yet its use outdoors remains largely limited, with only a handful of bridges, facades and pavilions built to date. The team is working to change that through durability testing and performance validation.
The research comes as New Zealand accelerates its adoption of mass timber in major public assets, including the new Parliament Building in Wellington, the country’s largest mass‑timber structure built to its highest seismic rating. The six‑storey Museum Street Building, covered by Wood Central last year, is being assembled “like flat‑pack furniture” using glulam and CLT from Red Stag Timberlab, as well as LVL from Nelson Pine. In July, Wood Central reported that crews began installing the first sections of the timber frame in May, with the project progressing zone by zone to maintain weather‑tightness and efficiency.
With early findings already influencing design decisions, the research is expected to progress into real‑world prototype testing and long‑term monitoring, with the potential to inform future revisions of New Zealand’s timber‑design standards
