New testing at CSIRO’s North Ryde labs promises to unleash new demand for cross-laminated timber (CLT) panels and lightweight timber-framed walls, thanks to a cladding system using stone wool that significantly enhances fire resistance. The results of the test will be announced at the Timber Construct event in Melbourne on 13-14 October.
The tests conducted by Australia’s Timber Development Association for Forest and Wood Products Australia have proved the material is superior to plasterboard, withstanding fire for well over three hours. The results also promise to make timber construction far safer, more acoustically sound and cost effective.
Among the outcomes of the research is that timber-frame assembled wrapped in stone wool managed 151 minutes of fire resistance, while 140 millimetre CLT achieved 182 minutes—far surpassing the Australian National Construction Code’s (NCC) minimum 45-minute requirement for external walls and 30-minute requirement for other areas.
(Mineral wool, or stone wool, or rock wool, is any fibrous material formed by spinning or drawing molten mineral or rock materials such as slag and ceramics. It was first manufactured in the 19th century.)
The CSIRO trials were conducted under AS 1530.4 compliance protocols, with researchers ensuring the critical timber surface did not exceed 300 ° centigrade for the specified durations.
Assemblies tested included a 90 × 75 mm timber frame fitted with 75 mm of either ROCKWOOL or DCTech VulcanWool, alongside CLT panels supplied by NeXTimber® and Xlam Australia. All specimens were exposed to temperatures replicating a standard fire curve, and thermal and acoustic performance were monitored throughout.
Andrew Dunn, chief executive of the Timber Development Association and specialist timber engineer, was present at the testing and said: “The standard requires the temperature to remain below 300 °C for critical durations, 45 minutes for external walls, 20 minutes for stairways, lofts and shafts, and 30 minutes for all other areas.
“Over the years, I’ve observed numerous timber tests, but the stone wool performance was extraordinary.”
Dunn said that stone wool’s inert mineral composition forms a protective barrier that slows heat transfer deeper into the timber core. The material’s fire-resistant credentials add to its thermal and acoustic insulation benefits, Dunn said.
And unlike fire-grade plasterboard _– which typically contributes to both fire spread and smoke generation when exposed to extreme heat – stone wool remains dimensionally stable and non-combustible. This dual performance profile positions it as a superior alternative for projects seeking higher fire ratings without compromising energy efficiency or sound control, according to Dunn.
Dunn will present the findings at the conference alongside Andy Russell, general manager of Proctor Group Australia/DCTech and Jeremy Church, the general manager of NeXTimber.
Russell said the fibre orientation and density gradients of the material optimised both insulation and value, and fire resistance performance.
According to Church, a bonus provided by the material is that for short spans in residential buildings, some form of insulated suspended ceiling would typically be required to meet acoustic requirements. With stone wool, there was “the potential to improve acoustic performance and fire rating level without the need for adding an additional layer of fire-grade plasterboard or increasing the thickness of the CLT substrate”.
The results will have significance for build-to-rent apartments, student accommodation and mid-rise timber developments, all of which are rising in popularity due to their sustainability credentials and faster construction times.
Factory-prefabricated timber components can be delivered with stone wool insulation already installed, reducing on-site labour and speeding up programme schedules while meeting stringent fire regulations.
Russell, who is a building envelope specialist, said the material also enhances the overall resilience and lifecycle performance of timber buildings. Its non-organic composition resists mould, moisture retention and pest infestation – challenges that have historically limited timber’s suitability in certain climates. By integrating stone wool into wall cavities and floor panels, designers and builders can deliver structures that meet both high environmental standards and stringent safety codes.
With timber construction continuing to gain traction as a low-carbon alternative to concrete and steel, the material looks set to meet demand from developers, insurers and regulators keen to reassess traditional fire-protection strategies in light of these findings.
As Church said: “We’re entering a new era where timber is not just viable, but competitive on every front – cost, speed, sustainability and crucially, fire safety.”