The cost efficiency of mid-rise timber structures

Timber mid-rise buildings are becoming the preferred choice for many stakeholders in Melbourne, due to a combination of factors, including cost-effectiveness, liveability, ease and efficiency of construction. Within the recent National Construction Code change, Deemed-To-Satisfy provisions allow mid-rise timber construction for buildings up to 25 metres “effective height” (typically, eight storeys).

The population of Melbourne is growing at the rate of 100,000 a year and maintaining the city’s reputation as one of the world’s most liveable will require urban infill, with an emphasis on less intrusive mid-rise solutions. In this sector, timber has a lot to offer: an increasing body of evidence points to the advantages timber buildings can provide to their occupants, while also offering the environmental benefits of a sustainable, renewable building material with a low carbon footprint.

However, it’s when quality and cost are taken into account that property developers become interested. Typically, the cost benefits of timber construction come from a combination of factors, including reduced preliminaries, direct material savings, easier off-site prefabrication, fewer variations and a simpler execution of follow-up trades, as demonstrated by a range of successful projects.

Most design and construction professionals in Melbourne know about Lend Lease’s Forté Living apartments (Figure 1), completed in 2012. This Cross-Laminated Timber (CLT) project delivered a 30% reduction in the overall time scheduled for an equivalent concrete-based program and was erected by a crew of only four carpenters and an operator for a small remote control crane. Based on the success of Forté, Lend Lease have several similar developments currently underway in Australia and more planned globally.

Another remarkable result was achieved by Australand in 2015 with The Green (Figure 2), on the Tullamarine Freeway. This is a five-storey residential building based on traditional lightweight timber framed walls and pre-fabricated composite cassette floor elements. The Green delivered an overall saving of 25% in construction costs, compared to another building with equivalent performance specifications and finishes that Australand completed soon after.

The major difference came from preliminaries (crane, scaffolding, site storage space, etc.) due to the reduced construction time and weights of unit components.

Currently, Sydney’s Strongbuild are achieving significant time and cost efficiencies in a large CLT social housing project (Figure 3) with respect to the conditions they offered to win the tender. Having almost completed the six-storey and the seven-storey parts of the three-building, 101-apartment complex, they are already 3 months ahead of schedule, mostly because they did not have any significant variations so far.

This is a relevant feature of timber construction: even a low level of off-site prefabrication can significantly improve accuracy, resulting in easier and quicker installation sequences, with fewer delays, minimum corrections and material waste.

Engineered wood products can also provide cost-effective elements for equivalent performances in a direct comparison, as it was the case for a 140-apartment development in Milan, Italy (Figure 4) delivered in 2011. This project, which features a flexible floorplan layout, optimising the mix of dwelling typologies and building services locations, dictated a structure which was 19% cheaper to erect in timber than in concrete. It effectively opened the path to a “cultural shock” for Italian building industry, resulting in several similar projects in the following years.

Updating a feasibility study after the code change, an independent quantity surveyor (http://www.mbmpl.com.au/) conservatively calculated a benefit of 10% for light frame timber construction in comparison to concrete for the building described in Figure 5.

Cost efficiency adds to the many environmental benefits of building with timber, a sustainable, certified and fully renewable resource, allowing for high thermal efficiency and distinctive beneficial effects on acoustics and indoor air quality, as summarised in a Planet Ark report.

Timber structures are becoming the preferred choice for mid-rise residential or commercial projects worldwide, aimed at achieving environmentally focused “green ratings” while keeping cost, delivery terms and quality within specifications. Timber construction is therefore on the rise, with an 18-storey building just completed in Vancouver, Canada (Figure 6), while projects for 30, 50 and even 80 storeys (Figure 7) are being investigated through sound design partnerships, backed by innovative builders and developers.

WoodSolutions’ free advisory program, started just a few months ago, is providing inspiration, evidence of suitability and design resources to many building professionals in Victoria, with no reference to specific product brands and the only aim to disseminate technical information applicable to projects in the early stage.

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