Ever since Lend Lease built its Forte apartment complex in 2012 using cross laminated timber (CLT), the use of wood and especially engineered wood/mass wood products on multi-storey buildings throughout Australia has taken off.
As at June, a total of 52 mass timber projects were either completed or underway involving 56 buildings. This includes 19 houses, 12 multi-residential complexes and a raft of other public and commercial buildings.
Because of their light weight, timber buildings can get by with a smaller foundation compared with those constructed of steel reinforced concrete. Especially if prefabrication is used, the wood industry says timber buildings can be erected more quickly than concrete ones.
On the Forte project, Lend Lease says it shaved four months off its construction time frame by using prefabricated timber. This saves on costs such as labour, crane hire, scaffolding, and site management. With commercial buildings, the faster construction also enables corporate landlords to open the doors sooner and bring in rent-paying tenants earlier.
The concrete industry disagrees. For a raft of reasons, concrete industry lobby groups say their product remains the most cost effective over the building life cycle. These include its durability, its relatively low levels of required maintenance and the fact that concrete, unlike timber, does not rely on additional fire protection measures to enable it to meet building code requirements.
This raises an important question: is timber really cheaper? What does the evidence say?
Not surprisingly, the timber industry says it has evidence that yes, timber, if used in the right applications, can save money.
Back in December 2015, Wood Solutions published the results of a research project which it undertook in conjunction with the Timber Development Association NSW and the University of Technology, Sydney (UTS). Under that project, it compared the cost of timber, conventional steel or concrete construction for four different building types. These included a medium rise seven-storey office building, an eight-storey apartment building, a two-storey aged care facility and a single storey industrial shed. Each solution was designed by independent architects and was independently costed with input from the Royal Institute of Cost Surveyors (RICS). A reference location in suburban Sydney was used for all four building types.
In all four cases, the results favoured timber.
For the seven-storey office building, timber construction was shown to deliver cost savings of $901,565 or 12.4 per cent on the overall project cost when compared with concrete. Whilst columns under the timber construction were more expensive to the tune of $158,000 and involved the cost of connectors ($59,769) and termite and fire engineering ($50,000), this was offset by savings on the floors $168,310, roofs ($129,764) and lifts, stairs and air shafts ($382,922).
The largest component of the cost saving for timber, nevertheless, involved savings due to preliminary costs such as scaffolding, site accommodation, hoists, craneage and construction site administration. These costs can be saved with timber, Wood Solutions says, as prefabrication can be used to compress the construction program and thus reduce the build time as well as the build requirements. The savings on these preliminary costs amounted to $460,000.
Significant savings were also found for timber on the aged care and industrial buildings.
On the aged care building, savings of 16 per cent ($112,000) was found for the timber design compared with steel construction. Whilst steel framing was $92,237 cheaper compared with timber on wall construction, savings were made in timber in respect of upper floors ($162,000) and roofs ($41,000).
In the case the industrial shed, the design explored two different bay spacing arrangements in respect of the timber construction. Where a bay spacing of 6.67 metres was used, cost savings of 5.2 per cent ($11,827) were realised. When the bay spacing was increased to 10 metres, this increased to 10.4 per cent ($22,519).
The cost comparisons were closer, however, on the apartment building. Here, the cost of the timber solution was only 2.2 per cent or $110,478 lower than that for the reinforced concrete building. The most significant savings for timber was a $312,000 reduction in preliminary costs associated with what FWA says is a six week shorter construction program and thus savings associated with site management, site sheds and plant such as crane, hoist and scaffolding hire.
Other savings for timber include opportunities for a thinner and cheaper concrete transfer slab which was enabled due to timber’s relatively light weight and $304,000 in the load-bearing structure which occurred because of a reduction in the material required for the roof and core walls along with the removal of columns throughout the building by the use of load-bearing walls.
However, this was partially offset by other additional costs which were incurred under the timber solution. The most significant of these was $735,000 which was necessary because of the need for additional lining required for fire protection of the timber load bearing floors and walls.
Of course, it must be stressed that these cost comparisons are not unbiased. They were published by Wood Solutions, which provides information about timber and wood products and is funded by the Forestry and Wood Products Association of Australia, a timber industry lobby group.
That said, the study is given credibility by the involvement of UTS, which obviously does not have any vested interests in promoting wood.
In addition, these comparisons deal only with the cost of construction. For a complete analysis of the cost effectiveness of timber of otherwise, ongoing costs associated with maintenance and life span as well as building energy operations (heating and cooling) would need to be considered.
Internationally, evidence about any construction cost advantages for timber or otherwise is mixed.
Under two cost comparisons recently performed in the United Kingdom, the costs differences associated with timber as against other materials was found to be relatively minor.
One of these comparisons, performed by Rider Levitt Bucknall, compared the cost of traditional timber framing as against masonry for a two-storey, eight block apartment complex containing 32 apartments (four apartments per block). Under these cost plans, timber was found to be cheaper, but the overall difference was only 2.8 per cent even though there was a 19 per cent saving in program time. This meant that the overall cost difference was not massive.
The second compared the cost of CLT against concrete for a six-storey apartment complex. Under that comparison, each cost plan of the respective materials was shown to yield an almost identical project cost (the difference was 0.1 per cent in favour of timber).
In Canada, results have been more favourable for timber.
In a 2009 study, the City of Vancouver via the Urban Development Institute commissioned the BTY Group to compare cost plans for concrete, lightweight timber and lightweight steel for a six-storey apartment complex. This was undertaken at the time as part of considerations as to whether or not to allow six-storey buildings in timber.
According to that study, the cost plan using a wooden frame construction was around eleven percent cheaper compared with using concrete or lightweight steel. On average, wood frame construction would have cost CAD$236 whereas concrete and light steel would have come in at CAD$263 and CAD$264 respectively.
Whilst this study took place nine years ago, its author BTY Group partner Joe Rekab recently sad that similar comparisons today would most likely yield similar results – especially given a significant shortage of labour in Canada at the moment.
More recently, in the 2016 edition of its Construction Cost Guide, cost and project management group Altus Group looked at comparisons between concrete framing and timber framing for four-storey buildings and found that timber had a cost advantage of around one-third compared with concrete.
Even timber industry execs, however, question these last results. At the recent Frame Australia conference, Timber Development Association executive director Andrew Dunn told the audience that these results appeared to be “a little bit too much positive for timber.”
As with the Woods Solutions studies, these international studies looked at the cost of construction only and did not consider any cost differences between the materials from a maintenance perspective.
Of course, not everything falls the way of timber.
In the US, for instance, the 12-storey Framework building was slated to be the largest timber building in North America with 60 affordable apartments. The proposal recently fell through, however, amid what are believed to have been concerns about the cost of the project, which was put at US $567,389 per apartment.
Not surprisingly, concrete industry lobby groups dispute claims about timber being the most cost effective solution.
In a written response to questions from Sourceable, Cement and Concrete Aggregates Australia (CCAA) chief executive officer Ken Slattery said concrete remains the most cost effective solution for multi-storey buildings and that for a number of reasons, it remains the material of choice.
When looking at cost efficiency, Slattery said a direct cost comparisons for any building type need to be done on a project-by-project basis. These, he said, must take into account the entire program cost of a building (not just the frame or structural elements) and must take into account indirect costs such as well as life cycle and maintenance expenses as well as the costs of construction.
On these scores, Slattery said concrete has several advantages. Firstly, its inherent strength and durability allows for a longer design life with zero or little need for maintenance. Concrete doesn’t burn, is dimensionally stable and does not rely on additional fire protection measures to allow it to meet construction codes, Slattery says. When coupled with intelligent solar design principles, it’s high thermal mass also enables it to deliver low heating and cooling costs, he adds.
Meanwhile, Slattery says concrete offers several advantages in the construction process. Whether in in-situ or precast forms, concrete construction practices are well established and understood. This, he says, leads to shorter and more reliable construction cycles for concrete. As a locally sourced product, Slattery says concrete is readily available and is not dependent upon long and uncertain international supply chains.
Slattery says it is important to adopt a holistic view of the costs and risks involved when considering which material which is cheaper.
“Like many other decisions, it’s important that all associated costs and risks are considered,” Slattery said.
“When selecting materials, the cost must be assessed based on a project-by-project basis and consider the specific building under design. All initial and ongoing costs (both direct and indirect) should be considered.
“In the case of multi-storey buildings, it is particularly important to understand what additional costs will need to be covered to meet requirements such as maintenance, coatings to protect the structure, fire-protection requirements such as the requirement for sprinklers or shielding of structural members and other durability requirements.
He pointed to concrete’s durability, non-combustibility and low heating, cooling and maintenance costs, adding that floor coverings, paints and coatings are not needed with concrete.
“Naturally resilient, concrete offers protection against fire, floods and other natural disasters as well as against rotting and termites. This leads to enhanced occupant safety and a building that stands up for life,” he said.
“Concrete outperforms as a construction material and won’t burden building owners with constant repair and maintenance costs. It is the first choice for sustainable, cost effective buildings.”