Throughout much of the world and in Australia, the push toward a low carbon economy is growing.
This is no less the case with construction, where a 2019 paper published by the World Green Building Council found that buildings and construction activities account for 39 percent of worldwide carbon emissions.
As this happens, use of timber in multi-storey buildings is growing. In the Canadian capital of Toronto, Google backed Sidewalk Labs is proposing a $US1.3 billion masterplanned waterfront precinct constructed entirely with mass timber. In Australia, timber has been used on numerous medium-rise apartment complexes and is now being used in mid-rise commercial buildings.
Simultaneously, an industry supplying innovative forms of construction including prefabrication is emerging. In some cases, multi-storey buildings are being made entirely from timber. In others, timber elements are being incorporated into traditional concrete and/or steel structures in a hybrid arrangement.
At a webinar to be sponsored by timber systems supplier Tecbuild next week, several sustainable construction alternatives will be explored. In particular, Melbourne University construction management lecturer Chris Jensen will outline how new sustainable building methods can be adopted by industry. Phil Gardiner, principal director at WSP in Australia will explore structural alternatives for sustainable construction including timber, modular and hybrid systems. Finally, Robert DeBrincat, business development manager at Icon Construction, will look at how barriers to adoption of innovative construction systems for builders can be overcome.
In the leadup to the webinar, Sourceable spoke with Gardiner and DeBrincat.
Asked about hybrid systems, Gardiner says greater use of these is likely going forward.
According to Gardiner, buildings constructed of 100 percent timber have advantages in several areas. Along with environmental benefits (wood structures are great for storage of carbon, enjoy good thermal performance and avoid the need for intensive carbon emissions associated with concrete manufacture), timber’s light weight enables lower density foundations. The material also lends itself to prefabrication and straightforward assembly.
Nevertheless, pure timber systems have drawbacks in that they require more columns and the columns are generally much larger. This can necessitate a smaller grid and can restrict floor space.
Pure timber also presents challenges with acoustic and fire protection.
By contrast, Gardiner says hybrid systems can address these challenges whilst retaining much of the benefit associated with timber.
Take for example, an office building involving steel columns and beams combined with timber flooring systems – cassettes, CLT slabs or timber joists. Instead of spans which measure nine meters by six meters with pure timber, you might instead achieve nine metres by nine meters with your to 350 mm by 350 mm with the composite. Combined, these measures would enable both greater floor space and a larger grid whilst retaining the benefits of timber flooring. As well, a concrete screed could be added to improve fire and acoustic performance.
With concrete, meanwhile, Gardiner talks of having large spanning concrete beams with timber in between. These timber beams can also have concrete further poured on top.
In such setups, Gardiner says smart planning can result in concrete being poured only once. Under this arrangement, timber is used for the formwork but then forms part of the permanent structure and adds to the structural capacity of the slab when the concrete and timber and bond together. Once the timber in place, the concrete slab and beams are poured together without the need for props.
As well as being efficient, Gardiners says this type of arrangement can deliver good acoustic and deflection performance.
Asked about advantages of hybrid structures, Gardiner says they enable individual materials to be used where they add greatest value. He likens this to a football field, where team members are placed in positions where their performance is strongest.
On the flip side, these systems may require some compromises in sustainability performance and aesthetic value when compared with pure timber construction.
Using combinations of timber with steel or concrete also creates challenges with coordinating different structural trades.
When designing with timber, Gardiner says it is important to understand where and from whom the wood and connections will be purchased. Timber, Gardiner said, varies in properties and grade according to where and from whom it is sourced. Therefore, the product with which you are designing varies according to different suppliers. European softwoods, for example, are weaker than Australian hardwoods. Connections, as well, are proprietary in nature and vary according to their source.
Whilst prefabricated structures are straightforward to erect on site, meanwhile, the automated nature of production of these building elements means a significant volume of documentation and workshop drawings needs to be prepared upfront.
DeBrincat, meanwhile, describes an ‘innovation gap’ in construction compared with sectors such as manufacturing and retail.
Whilst the building sector has seen improvements in products, he says much of how we build has not changed in a long time. These methods involve in-situ reinforced structures, composite concrete/steel structures and prefabricated concrete precast.
DeBrincat contrasts these with more innovative construction systems. Examples include:
- Engineered wood/mass timber products such as cross laminated timber (CLT), glulam, and laminated veneer lumber (LVL)
- Prefabricated timber and light gauge steel frame systems which are like the domestic residential market are now being used in multi-storey/medium density construction.
- Panelised timber and light gauge steel framed systems to create entire wall panels and floor cassettes.
- 3-D volumetric modular systems for the construction of hotels, student accommodation and other repetitive structures.
- Prefabricated elements of buildings such as modularised bathrooms, modularised facades or prefabricated roofing systems or floor cassettes which are placed into buildings that are otherwise constructed using traditional means.
Speaking from a contractor viewpoint, DeBrincat these innovations can reduce construction timeframes and cost.
As things stand, however, barriers to take-up fall into two areas.
First, there is a lack of depth within the subcontractor base and supply chain of parties who can deliver these forms of construction. When pricing projects, DeBrincat says that head contractors aim for ‘coverage’ of between four to five subcontractors for each trade to ensure competitive tension for subcontractor work. This delivers a level of certainty about the builders’ own costs.
Such certainty is particularly important given the breadth of risk involved in project delivery along with builder margins which are so tight that any unforeseen delays can lead to cost blowouts and losses on the job.
With innovative construction, DeBrincat says coverage at this level does not yet exist. As a result, builders adopt greater caution when bidding and build greater contingency and margin into their bids. This can erode the cost benefit associated with these forms of construction.
Second, a further consequence of innovative construction forms being relatively new is a lack of experience in both design principles and design efficiencies with these types of systems.
With traditional construction systems, DeBrincat says designs have become efficient over the years as engineers and architects have become comfortable in designing for these buildings with relatively high levels of certainty and predictability.
With innovative construction, many designers are still learning, and comparable levels of certainty do not yet exist. As a result, engineers may be adopting greater conservatism regarding specific design elements on a project, which would not normally exist with a traditional structure.
To overcome these barriers, DeBrincat says several actions are needed. The entire industry needs to adopt a proactive mindset toward innovative construction. Levels of risk need to be properly understood, adequately managed and equitably shared. Builders themselves need to think about how to maximise opportunities from these innovative forms and what benefits they could derive in doing so. Finally, the true and realistic cost of non-traditional construction needs to be better understood.
On this last point, DeBrincat says that whilst prefabrication is often claimed to be faster and cheaper, the industry does not yet fully understand the realistic costs associated with these forms of construction. This, he said, will become clearer over time.
Through innovative construction, Australia can better are more sustainable buildings.
We must grasp this opportunity with both hands.