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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.

Select an image below to view a larger size version in the gallery.

Figure 1: Forté Living apartments in the Docklands brought modern mid-rise timber building in Australia. Photo: WoodSolutions.

6 comments

johnproctor's picture

my question is about weight. The most significant cost of over track development is the deck that must be built to support the building above.

If wood based construction is significantly lighter would that allow a simpler structural solution for the deck and improve the economics of these in fill proposals?

Federation Square East for example is effectively 'on hold' at the moment because the economics don't stack up due to the deck. Would wooden structures help to fix that?

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Paolo Lavisci's picture

Definitely yes, timber structures will help reducing the foundation costs, as it happened in a number of cases where the soil was poor or the construction was meant to be over a subway.
Both the Forte' apartments and the Library at the Docks did benefit from it.
See another good example at http://waughthistleton.com/dalston-lane/

Paolo Lavisci

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Sarah Bachmann's picture

Please would the author elaborate more on claims of 'high thermal performance'? The Planet Ark refers to a project that has a combination of earth covered roof, double glazed windows and massive timber beams to provide the building with excellent thermal performance.
Pease also elaborate on the fumes that might be emitted from a burning timber structure, particularly where the timber has been treated or glued, eg, CLT. How has this potential life threatening issue been addressed by the industry?
How does timber compare with say concrete from a durability perspective? I would have thought that concrete out-performs timber massively, given that it's not prone to termites, is flood resistant, fire resistant etc. That is why, for example, timber bridges are so often replaced with concrete bridges. And why we see so many concrete structures still standing some 5000 years later!
Finally, I also comment that other than crane cost savings, any other off-site prefabricated product (eg precast concrete) delivers similar time and cost savings to off-site prefabricated timber.

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Bilby's picture

Was concrete even in use 5000 years ago? Certainly Roman concrete (using volcanic ash rather than Portland cement) has stood the test of time - but that is more like 2000 years old. Concrete is preferable for civil engineering in part because of weather exposure, where timber tends to rot over time.

I'm not sure about the claim that precast concrete delivers similar time and cost savings to prefab timber - for one thing it is heavier and harder to modify on site, leading to more delays if changes need to be made. Also, concrete has thermal mass, but lacks insulation properties on its own, whereas timber inherently achieves greater R-values and helps to prevent thermal bridging within the structure.

As to the toxicity of the glue in glue laminated timbers, that is a relevant consideration, but the point is, timber gains its structural advantage in a fire due to its ability to char on the outside of the section only, protecting the inner structure even when exposed to high temperatures that would damage structural steel. So the amount of glue product burned in a fire where the structure remains intact would be minimal in comparison with the toxic fumes released from non-structural items, including furnishings, floor coverings, etc.

And then there is the issue of carbon emissions from concrete, vs the carbon sink represented by building with timber. Overall, timber construction has a lot of benefits that concrete and steel do not.

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Paolo Lavisci's picture

Thank you Sarah, as the CEO of National Precast Concrete Association your opinion is most valuable to me.
Planet Ark has recently updated their report (http://makeitwood.org/documents/doc-1501-wood---nature-inspired-design-r...) and refer to a series of buildings with quite different performance specifications and designs. My definition of “thermal efficiency” is “achieving a given performance, costs and wall/roof thickness by using a lower amount of materials and/or lower embodied energy”. Timber-based construction, with virtually no thermal bridges and very high thermal insulation, specific heat and hygrothermal buffering capacity, is undoubtedly far superior in terms of efficiency with respect to other building systems of equivalent cost. Not just in cold climates, but also in mild coastal climates like ours, where summer cooling often requires more energy than winter heating and concrete can provide some thermal mass, which is part of the equation.
Burning timber emits the same amount of CO2 that has been sequestered in it. Burning wood adhesives (in very minimal quantities in CLT) is like burning any other kind of similar plastics, with very low smoke toxicity. In the specific case of CLT, it’s either melamine (like most baby tableware) or polyurethane (like most paints for furniture and windows).
The Pyramids (which, I read, are the first documented use of concrete) have timber floors, props and beams, which still support the stones… and the Egyptians also invented plywood using fish glues. Besides this, reinforced concrete has a shorter application history than glued timber and not always a better durability record, especially in coastal locations. Durability is certainly much more dependent on the quality of design, installation and maintenance, than on the nature of the material. You may be aware that there are timber churches and bridges which are many centuries old, in China and Europe.
The savings in preliminaries, footings and erection shall be considered for a given project, as they may be different in a different context. But nobody can deny that an equivalent size slab or wall, which is 80% lighter, will result in a longer reach and a faster lifting time, using the same crane. Or allow for a much lighter crane.
In conclusion, my opinion is that every material has its qualities and functions within a well harmonised design, so timber and concrete will certainly coexist in the future much more than they already do.

Paolo Lavisci

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Paolo Lavisci's picture

Thank you very much Bilby, excellent comment !
You show a very good knowledge in materials and design... what's your activity ?

Paolo Lavisci

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