As part of the study "Commercial Building Costing Case Studies - Traditional Design versus Timber Project" (you can download it here) TDA (Timber Development Association) specialists have developed projects for four buildings of different typologies: a one-story large-span industrial building, a 2-story building for a care center for the elderly, a 7-story office building and an 8-story residential building. Each project was carried out in the usual reinforced concrete or metal structures and in glued timber. When comparing the estimated calculation of all design solutions, it turned out that the wooden version of all four types turned out to be cheaper: the cost of a wooden residential building was lower by 2.2%, a production building - by 9.4%, an office building - by 12.4%, a care center for the elderly - by 13.9%.
Fitzpatrick + Partners and Studio505 took part in the research as architects, design solutions were worked out by Arup, TTW, AECOM, Meyer Timber, TDA, Nelson Pine Industry, engineering communications and acoustics were handled by Arup, the research methodology, together with all of the above partners, was developed by the Sydney University of Technology, the construction cost estimate was carried out by the Royal Institution of Chartered Surveyors (RICS). For public and residential buildings, costs related to heating, ventilation, air conditioning, facade and acoustic solutions were also taken into account.
It is important that the research focuses specifically on the cost of building a building and does not take into account the environmental component of timber construction, which is usually emphasized by proponents of timber construction.
The project of the center for the care of the elderly with a total area of 1,681 m2 was made in wood and metal frames, while all other elements - the foundation, the floor covering of the first floor, exterior and interior finishes, engineering systems - remained unchanged in both cases.
Calculations showed that a wooden solution can save 15% to 20%, but considering that a wooden wall structure increases costs by 33%, the total cost of a wooden building is 13.9% less than a metal one. At the same time, the difference between the market value of materials for the frame (excluding construction costs) is even greater - 20% or 37,867 Australian dollars: steel frame - $ 231,000, wood - $ 193,133.
In an 8-storey residential building with a total area of 6080 m2, the first floor is occupied by commercial spaces (348 m2), the remaining seven floors are apartments (5320 m2), and a car parking is located on two underground levels.
In this variant, the main savings are accounted for by the supporting frame (39%), the load-distributing reinforced concrete floor of the first floor (due to the lower weight of the wooden structure, a thinner slab is used, the cost of which is reduced by 13%) and preliminary costs (construction time of a wooden the load-bearing structure is six weeks less than reinforced concrete, which together with the ease of installation of the elements saves $ 52,000 per week)
The additional costs of erecting a wooden structure are the need for fire protection measures - in this case, special finishing of the floor and ceilings. Also, for a wooden building under construction in Sydney, protection from termites is necessary: the reinforced concrete elements in contact with the ground are protected with stainless steel mesh, which costs $ 15,000.
The office building project includes 7 above-ground floors and 2 levels of underground parking in a reinforced concrete version. Fire protection is achieved by increasing the cross-section of structural elements, and not by finishing.
Compared to reinforced concrete, the wooden solution of an office building saves 3.8% on ceilings, 32.6% - on stair-elevators and ventilation shafts, 18.8% - on roof structures. Additional costs are incurred on columns (67%), connectors and fire and biological protection.
In this example, one of the important conclusions of the study comes to light: a more economical fire protection is an increase in the cross-section of structural elements, as in an office building project, and not covering them with plaster, as in a residential building.
The researchers note that often the choice of building material is governed by its net cost, which is usually higher for wood: for example, a cubic meter of reinforced concrete, coupled with logistics costs, will cost $ 200, while cross-glued panels (CLT) - $ 1,500. However, this difference is compensated by seemingly non-obvious savings on upfront costs: ease of construction, reduction in construction time and the number of workers, use of simpler lifting equipment.
Work on the construction site is limited to assembling and joining prefabricated elements: a fast, clean and quiet process, unlike working with reinforced concrete. Also, due to the difference in the mass of the structure, the costs of the foundation are significantly reduced (while the same foundation was used during the experiment for the wooden and traditional versions), the costs of lifting equipment are reduced: instead of expensive tower cranes, cheaper and simpler cranes of small sizes are used.
The main problem of timber construction, according to the authors, is not its high cost, which they proved in their research, but the inertia of professionals. Experts prefer to work with standard, carefully studied technologies, while glued timber structures are relatively new, and therefore not everyone understands well how they work: when faced with wood, engineers become conservatives.
Researchers from TDA see a way out of this impasse in an open professional discussion, free exchange of experience and developed engineering solutions on public sites. And we fully support them in this.
