Costing Timber

COSTING TIMBER

Forté Apartments image

Architect was Andrew Nieland/Lendlease. Photography by Emma Cross.

It seems not a week goes by without the announcement of another engineered timber project around the world. Recent decades have seen incredible growth in engineered timber projects, with significant buildings of up to 10-storeys in the UK, structures of up to 18-storeys in Canada, and a plethora of projects in Europe (including Mjøstårnet which, at 22 storeys, will be the tallest in the world when completed later this year). As ever, Australia is near the front of the pack, with significant projects in Melbourne, Sydney, Brisbane, Adelaide, and soon Perth.

While timber structures have been utilised for buildings of all classes around the world, Australia has seen most focus on buildings in Classes 2 and 3 (multi residential/short term residential) and Class 5 (offices). Indeed, most building designs can be optimised to suit engineered timber systems, which can deliver both the open, flexible spaces afforded by a column and beam design (with a 9m x 9m grid now common), or the high performance, comfortable spaces resulting from loadbearing-wall structures, where timber panels are utilised to deliver efficient floor and wall elements.

Both of these structural systems have been widely utilised to successfully deliver state of the art projects, with panelised construction used for multi-residential, accommodation, and education projects throughout the country (e.g. Forte, The Green, and Monash University Student Accommodation in Melbourne to name a few). Furthermore, column and beam designs have been utilised to deliver some of the country’s most photographed office projects including International House (Sydney) and 25 King (Brisbane).

WHAT IS ENGINEERED TIMBER?

Engineered timber products are not particularly new to the world. In fact, all products we commonly see used in mid-rise projects were developed in the 20th century (Cross Laminated Timber, the most recent addition to the family, emerged in the 1990s), meaning they have all been tried and tested in structures for at least twenty years.

Engineered timber products can be divided into two main groups: ‘Massive’, and ‘Light-weight’ systems. The term ‘Massive’ timber refers to “an element not less than 75mm thick as measured in each direction formed from chemically bonded laminated timber” (NCC2016) and includes products such as cross laminated timber (CLT), laminated veneer lumber (LVL), and glue laminated timber (Glulam). Each of these products excels in different areas of structural use, and as such, timber designs will typically utilise a mix of two (or sometimes all three).

CLT, often described as ‘jumbo-plywood’, is manufactured by gluing and pressing three or more layers of timber boards that have been arranged so each layer is perpendicular to the last. This twoway strength makes the product highly efficient in shear, and well suited to panelised use in walls or floors.

LVL is also produced as a panel, however consists of many thin veneers that are oriented to parallel and are then glued and pressed together in thicknesses of up to 75mm. With all (or most) veneers aligned in the same direction, LVL is incredibly strong as a beam, column, or one-way slab.

Finally, Glulam comprises lengths of timber which have been aligned in the same direction and glue laminated to produce high strength linear sections which are typically used as columns and beams.

The lightweight alternative to the above ‘massive’ systems, sees wall stud frames (consisting machine graded pine or LVL studs) and floor cassettes (consisting high span floor joists which are pre-fixed to a flooring panel for speedy installation) utilised in a panelised fashion. While perhaps lacking the natural beauty of the massive options identified earlier, this system is highly efficient and structurally sound in buildings of up to eight storeys. With capacity within the industry to fabricate wall frames and floor cassettes in a highly efficient frame and truss plant, the lightweight solution is an attractive option for most mid-rise Class 2 and 3 buildings.

So how is costing timber different to costing any other building material? In reality, it’s not the timber that changes things, it’s what the timber allows the design team and builder to do.

International House Sydney

Designed by Tzannes architects for Lendlease. Photography by Ben Guthrie.

Engineered timber products are fabricated to order, facilitating further prefabrication if required, they are light (timber is 20% the weight of reinforced concrete), they are easy to fix to (think an impact driver and some screws rather than a hammer drill and epoxy), their assembly requires no wet trades or hot works. They can be lifted with edge protection pre-installed, essentially avoiding live edges altogether. What’s more, timber floor panels (whether massive or cassette) require no propping, meaning services rough in can commence the day after a floor above is installed.

When combined, these factors have been seen to result in on site programs that are almost a third shorter than if the building were built following traditional in-situ techniques. This saving is well illustrated in the case of Forte, Australia’s first mid-rise timber project. Constructed by Lendlease in Melbourne’s Docklands in 2012, this 9-storey project was installed on site by a team of up to 6 people (including crane crew) in just 10 weeks.

This time saving directly impacts all time related costs in the project, including preliminary costs for the builder, interest costs for the developer, and risk exposure for all parties involved.

While time savings generally account for the largest proportion of cost savings in a timber project, other characteristics unique to timber can result in further savings. For example, the light weight of timber means that massive timber panels rarely exceed 2 tonnes, and lightweight panels rarely exceed 1.5 tonnes. This comparatively small weight allows for the use of lower capacity cranes on a project, reducing both the weekly hire and footing costs.

Importantly, the prefabricated nature and low weight of timber elements has been found to result in incredibly safe sites. With a supervisor to worker ratio many times higher than experienced with larger structure workforces, no live edges, no high-risk trades, and on site cutting kept to a minimum, timber construction sites experience reduced occupational health and safety risks to all workers on site.

WOODSOLUTIONS’ ROLE

The most important stage of a timber project is right at the start. It is important that timber projects are costed with the material, and what it means for a project in mind (this must also be considered in the design). If used correctly, timber construction can be faster, safer, quieter, and ultimately cheaper than traditional systems - WoodSolutions is here to help this happen. The WoodSolutions Mid-rise Advisory Program team has offices in Melbourne and Brisbane. The team is available to provide free project-specific advice throughout all stages of a project. With expertise in costing, programming, engineering, planning, design, and construction, the team is well equipped to support you through your next timber project – simply contact us at info@ woodsolutions.com.au