A fire broke out on the NZ International Convention Centre roof in October 2019. Photo / file
A fire broke out on the NZ International Convention Centre roof in October 2019. Photo / file
It’s become like folklore now for New Zealand’s biggest repair job: people talk about straw in the NZ International Convention Centre’s roof and that it’s what made it flammable and defective.
The story goes that the architects and builders behind the city’s biggest new commercial property project specified and putstraw in the roof, which pretty much anyone knows is a daft thing to do, right?
And that it went up like crazy in the destructive fire four years ago.
Does the Three Little Pigs story need retelling, anyone?
Builder bosses didn’t expect the new roof to contain straw on the Nelson/Hobson/Wellesley Sts site.
It’s folklore now, part of the building, often repeated, those close to the project say.
The only trouble is: it’s untrue.
In 2020, the Herald reported how the jury was out on whether the same roof would go on, having been made of bitumen, rubber, plywood and a highly compressed straw-like substance.
Those are the materials which burned so fiercely when the roof caught alight and subsequently burned for 10 days. The complexity, size, design and composition are factors partly blamed by experts for the fire’s ferocity and duration.
The Australasian Fire and Emergency Service Authorities Council fire review cited the roof design and materials as factors which contributed to the fire’s complexity, duration and Kiwi firefighters’ inability to create a fire break to stop it from burning. The “compressed straw-like product” inside that roof and its composition had an effect on attempts to extinguish the fire, that report said. Plus that straw material became extremely heavy when water-laden, creating other issues.
“The skeleton of the roof had thousands of metres of high-grade timber to support its top layer. The roof was ‘non-walk on’, engineered to carry less than 75kg/sq m,” the report said.
A roof with the same product containing straw is going on.
John Salier, executive project director for Fletcher Construction, said today there was nothing particularly unusual or unorthodox about the design, materials or the way it’s built, neither pre-fire or these four years later.
The roof product Durra Panel has straw for thermal, acoustic dampening and sound absorption properties. It was on the NZICC roof pre-fire - and is going back in post-fire, although the design is changing.
Work on the NZICC - one of New Zealand's largest building jobs. Photo / Jason Oxenham
“It was originally chosen and has since been reaffirmed for its acoustic, thermal and sustainability benefits. It’s made from compressed straw and contrary to some reporting is naturally fire-resistant,” Salier said.
Durra Panel has been used for similar purposes in many large-scale projects across Australia and in New Zealand, he stressed.
The NZICC was originally put at $750m but a $336m fire claim was made and now Fletcher Construction has estimated a further $150m will need to be spent. Those figures add up to a total cost of around $1.2b although SkyCity Entertainment Group isn’t saying if those numbers should be added together to reach that new total.
Fletcher’s John Salier answered some key questions about the project.
Q: Has the roof design changed from the original pre-fire design?
Salier: “The original roof design included materials and methods commonly used in New Zealand at the time of design in 2015/2016. But after discussions with project stakeholders and recognition of transformations in design trends since 2015, Fletcher Construction decided a change in roof design would provide reassurance to all involved parties, mitigate construction risk with the reduction of combustible materials and deliver a faster, more efficient, construction.
“The new design also uses common building materials and methods. As an example, the new water-proofing membrane system is a peel-and-stick single-layer FiberTite (thermoplastic) product that’s applied with a heat gun, rather than the original system which was a torch-on bitumen product.
“A significant benefit of the new roof design is the method of construction. The new design replaces the timber section of the roof with a corrugated metal product - tray deck - which means we’ll be able to finish the project faster. With the original timber design, we had to finish the whole roof before it was waterproof underneath. The tray deck effectively seals the top level of the convention centre and theatre while we complete the remainder of the roof. This allows us to work on both sections at the same time. That gives us a significant time-saving.”
Q: Is Durra Panel still being used for acoustics?
Salier: “Yes. Underneath the main roof membrane, is the product Durra Panel used to provide thermal and acoustic protection to the plenary theatre which sits below. It was originally chosen, and has since been reaffirmed, for its acoustic, thermal and sustainability benefits. It’s made from compressed straw, and contrary to some reporting, is naturally fire-resistant. Ortech is the Australian company that produces the product.
“Their technical manual says Durra Panel combines the desirable properties of low embodied energy, strength, impact resistance, thermal and acoustic insulation together with a high degree of fire resistance. They go on to say ‘the carbonising action of the straw core when exposed to flame retards fire penetration of the panel’. Durra Panel has been used for similar purposes in many large-scale projects across Australia and in New Zealand.”
Q: Did Warren & Mahoney design a new roof?
Salier: “As lead design consultants for the NZICC, they were part of a multi-disciplinary group of consultants involved in the re-design of the roof.”
A construction professional thinks that last answer means it was Fletcher who led the impetus for the new design.
