25-Metre Tall Timber Construction: The Design Opportunity 1

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Monday, October 12th, 2015
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We are on the cusp of a major change in Australian construction.

With public comment period now closed, industry insiders report great confidence that the Australian Building Codes Board will adopt a new voluntary deemed-to-satisfy (DTS) solution in the BCA for timber building systems in apartment, hotel and office buildings up to 25 metres in effective height (approximately eight storeys). The proposed solution, consisting of the use of appropriate layers of fire resistant plasterboard and sprinklers, will cover both timber framing and massive timber systems. Timber building systems are currently restricted to three storeys.

So why is this important? When construction costs are projected to escalate at a rate of four per cent per annum in NSW for the remainder of 2015 according to the WT Partnership, that equates to over $13,000 annual construction escalation on a typical two-bedroom, mid-range apartment. I believe any new technology that reduces construction time and hence cost is welcome, as the current building boom continues unabated.

The labour and materials of a structural frame typically accounts for between 13 to 15 per cent of total construction cost, but erection can account for a third or more of the overall construction programme. By the time a structural frame is complete, having bought their land and paid for design and gain approvals, a developer will typically have spent around a third of total project hard costs. So as the S-curve of construction costs exponentially increases once the frame is up, so too does the sum of finance costs, holding and equity opportunity costs. At this point in a construction programme, savings in erection time capitalise into significant real dollar value for the builders and developers involved.

As housing affordability is being hotly debated in the property industry, much of the discussion seems to get hijacked by various interest groups, often into indirect factors and hobby horse issues – whether that be the planning process or state taxes or negative gearing. For my money, reducing the cost of construction is a surefire and direct way of influencing property cost outcomes. There are proven ways to do this on appropriate projects if builders are prepared to adapt to new technologies.

Many assertions have been made independently and in many countries about the cost and time advantages of timber multi-storey construction over other common construction methods. Mid-rise timber construction regulations have been in place for many years in Europe and the Americas, so their experience is perhaps a guide as to what we should expect here.

That experience is backed by a great deal of supportive academic and industry research. Comparison of construction techniques is a challenge and some research has gone to incredible lengths to prove the timber value proposition.

For instance, an early research feasibility study called the TF2000 Project which was carried out in the UK involved the construction of a full size, six-storey experimental light timber frame building inside an aircraft hanger. It was the first of its kind in the world at the time in 1997. The sole purpose of this was to investigate the performance and economic prospects of medium-rise timber frame buildings for the UK market.

The research made findings on lead time, construction value and speed of construction. The start point was the arrival of the structural frame on site and the end being a watertight timber frame. It took just 17 days to erect a six-storey building of 24 flats with a team of just six erectors. The construction rate was 656 square metres per week compared with a comparable concrete structure of 333 square metres per week.

Granted, the above was set in controlled conditions, but are great results in the UK able to be replicated in Australia? Perhaps the poster project for achievement of time efficiency with timber construction is Australand’s The Green project. This five-level light timber frame construction of GFA of 5,100 square metres went up on an average, 11-day floor cycle using prefabricated Tecbeam cassette floors and load bearing wall frames, saving over 12 per cent on the programme compared with a best case concrete frame alternative.

Cost benefits have been assessed and reported time and again around the world, most recently in this year’s detailed cost comparison of steel, concrete and timber building systems by the Royal Institute of Chartered Surveyors. There are no prizes for guessing that timber was yet again proven to be the lowest cost structural system.

One would think it a foregone conclusion that a cheaper, quicker structural system, with a ready pool of trade labour that can be sourced domestically, as well as commercial trade work force, would be the natural choice of most builders. The fact that the majority of projects for which timber is a suitable alternative – low to mid rise, suburban developments, are still designed in concrete, is a testament to the entrenched work practices and snail’s pace of meaningful innovation in what is still an industrial-age arena. Facts cannot be ignored indefinitely, however, and I am convinced that as the current apartment boom tapers and the design and construction sectors are forced to sharpen their pencils, light timber frame construction in multi-storey projects will increasingly become the preferred system of choice.

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  1. David Bowers

    Jack
    If you are going to quote the TF2000 project, you should also run an article on some of the downsides to large timber frame buildings that have succumbed to arson during the construction stage. The UK structural timber association has come up with a range of measures to mitigate against this problem but arson is a very real risk to partially completed large timber structures. A quick google for "Hendon police college fire" will give you an idea of the amount of heat a large block of flats gives off in a very short time and the risk to site personnel and surrounding buildings.
    As I said above there are now a range of measures in place to limit the impact of arson during the construction phase but these need to be adopted at a very early stage in the development.