Dr Andy Buchanan talks about the need for an updated Building Code to address timber structures, the challenges of encapsulation for mass timber structures, and how a structural engineer discovered wood and fire.
At the Fire NZ Conference, Andy will be speaking on the topics of “Fire Safety Engineering in Mass Timber Buildings – issues and solutions” (together with Dr Colleen Wade) and “Encapsulation for mass timber structures”.
A principal at PTL Structural Consultants, Christchurch, He is the co-author of Structural Design for Fire Safety (2017) and the New Zealand Timber Design Guide (2007). He is also a co-author and editor of the just published Fire Safe Use of Wood in Buildings: Global Design Guide (2022).
Andy holds a B.E. with Honours from the University of Canterbury (1970), a masters degree from the University of California at Berkeley (1972), and a PhD from the University of British Columbia, Canada (1984). He was previously Professor in Civil Engineering at the University of Canterbury.
FNZM: Where did your structural and fire engineering journey begin?
AB: I graduated in 1970 from the University of Canterbury with a degree in Structural Engineering, which was mostly concrete buildings and earthquakes. When I went to California to do my master’s degree, to my surprise I was offered a project on fire safety – I had no idea that there was any such thing as fire engineering back then!
Although this introduced me to fire engineering, I didn’t think it was a career, so I stored it away, came back to New Zealand and worked for a big consulting firm doing structural engineering – more steel and concrete.
Nevertheless, I slowly got interested in wood, initially from conservation of a renewable resource, then as an engineering material. I then went off to Canada where I did my PhD in timber engineering.
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FNZM: Why Canada?
AB: A visiting Canadian professor was giving a talk to the Canterbury structural engineers about timber engineering. I struck up a conversation, and he said why don’t you come over to Canada? So off I went with a young family to study in Canada for four years.
Canada is a bit like New Zealand, it’s got lots of forests, and forestry is a huge part of the economy. The Canadian government still owns many of their forests and even now is investing to add value to them.
Having completed a masters degree in fire engineering and a PhD in timber engineering, I came back to New Zealand and did some consulting. I was then offered a position at the University of Canterbury in 1987, where I was given the freedom to develop teaching and research in both fire and timber engineering.
I established the fire engineering masters programme at UC 30 years ago. It’s a fantastic programme. It was one of the first in the world. It was started in collaboration with the Fire Service Commission who provided funding, and we hired fire engineer Charley Fleischmann, who came to New Zealand from the US to set up and run the program.
It’s been a fantastic collaboration with the fire service extending throughout the past three decades. I’ve lost track of how many hundreds of graduates there are.
FNZM: Timber really appears to be ramping up as an area of focus.
AB: I’ve had a professional career as a structural engineer where my expertise has been in fire engineering and timber engineering, and ultimately those two interests came together, for obvious reasons.
There are going to be more and more timber buildings as the climate crisis crunches. Just as we’re moving from petrol cars to electric cars we’re moving from steel and concrete buildings to timber buildings. Wood burns, and that raises all sorts of questions about fire safety.
I’ve been part of an international group, the Fire Safe Use of Wood Group, that decided three or four years ago to collate all the international research and publish some guidelines – Fire Safe Use of Wood in Buildings: Global Design Guide. It was published this year, and although it doesn’t provide all the answers, it does give the current state of play.
The next hurdle in New Zealand is to get the Building Code authorities to realise that all these timber buildings are coming. The Building Code, and especially the fire part of the Code, was written decades ago when the authors had no idea that there were going to be all these buildings built of stuff that could burn. The Building Code is out of date.
FNZM: So the current setting of the Building Code are needing to be changed. What’s required for the regulatory changes to happen?
AB: It’s never easy to make regulatory changes. It’s particularly difficult in New Zealand because some of our fire safety requirements are very permissive compared to regulations in other countries, especially for tall buildings.
Most countries in the world say that if you have combustible building materials you can only build to a certain height. But in New Zealand there’s no such limit. Other countries say the taller you go the more fire resistance you have to have. In New Zealand we don’t have that.
It’s not going to be an easy transition out of this because as soon as you start saying we need to toughen up on these requirements it puts everybody in an awkward position. We see it in what’s happening in Wellington now with the increased earthquake requirements. It creates the impression that the previous designers weren’t doing their jobs well and that all the existing buildings aren’t safe enough.
It’s easy to relax Building Code requirements but it’s not easy to make them tougher. Nevertheless there are going to have to be some changes.
In my semi-retirement I am working towards the creation of an environment where we can provide adequate fire safety in the large and increasing number of timber buildings and do it in a rational sensible way in which we balance the risks.
FNZM: Your other talk is on “Encapsulation for mass timber structures”. What’s that about?
AB: If you read the literature about all of the wood in timber buildings contributing to the fire load, well, you cover it up, you encapsulate the timber with Gib board. But then, how much of the wood do you have to cover up? How many layers of board do you have to cover it up with? And how to you calculate that? It’s not simple.
If you cover up the wood with several layers of board then you remove one of the big concerns with timber buildings, which is the problem of timber adding fuel to the fire.
The problem is that architects and building owners know people love wooden buildings and want to show off all the wood. In contrast, the fire engineer wants to cover up all the wood – the more the wood is covered up the safer the building. So there’s a tension there, and that’s what my paper is about.
FNZM: How do you get around that tension, or is it always going to be there?
AB: It’s always going to be there. The answer really comes back to performance based design. When there are rules in the Building Code for fire safety there are two approaches: a prescriptive approach and a performance-based approach. In terms of the latter, the Building Code states the performance requirements and then the fire engineer can use whichever method he or she likes to meet those performance requirements.
In the Building Code environment the prescriptive solution is called an ‘acceptable solution’ and the performance requirement uses the ‘verification method’ or an ‘alternative solution”. To use performance-based design requires a lot more calculations, so the fees are going to be higher and it’s going to be a much bigger effort. You don’t need to do that for every garden shed, but if you’re designing a skyscraper you certainly do need to.
The Building Code documents need to provide guidance to allow the tension to be balanced off, taking into account the height and size and use of each building.
