Is it commercially viable?
Although the technology is very new and only a small amount of commercial data exists, recent comparisons suggest that the same building constructed from steel, reinforced concrete or post-tensioned engineered timber (EXPAN with Pres-Lam) all cost about the same for total out-turn cost. Feedback from constructors that have built recently constructed EXPAN buildings consistently indicate that construction time is rapid and crane times and capacities are all reduced compared with building a similar structure in pre-cast concrete. These and other factors can be expected to result in the engineered timber option being very, if not the most competitive option for a long-span, open plan low-medium rise building.
Is it “green” and sustainable?
The engineered timber option provides the easiest, most competitive way of achieving a carbon neutral building (cradle to gate). All our research and development to date has focused on the use of engineered timber made from pinus softwood grown in sustainably managed forests in Australasia. Recent comparative studies show that a multi-storey engineered timber building easily achieves carbon neutrality with the sequestered carbon present naturally within the harvested logs off-setting the CO2 emissions associated with the selective use of reinforced concrete in the foundations and timber-concrete-composite floors and steel, glass and aluminium used in the roof, cladding and joinery components of the building.
The same study indicates that the carbon footprint of a multi-storey engineered timber building over its full lifetime (ie. including all operational energy use) is around 1.69 tonnes CO2 eq. / m2 and this is more than 13% less than the carbon footprint of the same building constructed from steel.
Timber is a renewable building material which is in plentiful supply from sustainably managed and certified forests throughout New Zealand and Australia.
Is it low energy use?
The buildings are designed to a high performance specification with high levels of insulation, maximum use of solar gain and double glazing throughout. This minimises heat loss by the building and ensures energy costs associated with heating are minimised.
Does it have good inter-floor acoustic isolation and dynamic response?
Inter-floor acoustic isolation is an important characteristic of any building complex that is potentially available for mixed use. Sound is transmitted as air-borne and impact induced air pressure fluctuations and is essentially transmitted from floor to floor in multi-storey buildings directly through the floors separating the storeys and via flanking paths involving the connections between floors and other components of the building. EXPAN quiet floors in engineered timber and timber-concrete-composite (TCC) constructions are specifically designed to minimise acoustic transmissions from one storey to the next whist at the same time providing for long-spans that enable open-plan and flexible use buildings with few load bearing walls. The TCC constructions utilise the concrete mass to absorb acoustic energy and the combined capacity of the engineered timber and the concrete to limit floor deflections and provide the required structural capacity, whilst minimising the total floor unit depth. Suspended ceilings or raised floors are also an option, providing for totally hidden services and facilitating a space for additional acoustic absorption if required within a given specification.
Dynamic or vibration response of floors is also an important characteristic that influences both quality perception and overall flexibility of use. Engineered timber and TCC floors are critically designed to ensure that the resonant frequency response of floor modules exceeds the minimum acceptable threshold frequency, ensuring user comfort and confidence.
Is the technology proven?
What data or supporting evidence do you have for the new system? Are there any existing examples that I can view?
The EXPAN with Pres-Lam engineered timber system has been and continues to be the subject of extensive engineering research and development. The Structural Timber Innovation Company Ltd has been investing in the research for the past 3 years and Canterbury University for several years preceding this. Many of the fundamental principles have been tested experimentally under laboratory conditions and there exists substantial data and results that supports the characterisation of the system and the claimed earthquake resistance performance. In addition to this many internationally peer reviewed journal papers on the subject have been published and the universities involved in the research work, Canterbury University, Auckland University and University of Technology Sydney are recognised as leading edge in this field of engineered timber construction.
The technology is new but there are now existing examples of these buildings that can be inspected. The NMIT Arts and Media building is the first commercial building in the world that incorporates the EXPAN with Pres-Lam technology and this building was officially opened on 31st Mar 2011. Additional examples presently under construction and nearing completion are a new building at the BRANZ headquarters in Porirua, just out of Wellington, the Structural Timber Innovation Company’s EXPAN building constructed on the Canterbury University campus and the Tumu ITM building, currently under construction in Napier/Hastings.
Is it durable? Its timber, won't it decay?
The architectural design of the buildings is such that the engineered timber forming the building structure is all contained inside the building envelope. This means that the engineered timber can be untreated and will not be subject to fungal decay as it will remain dry and protected from external moisture and weather conditions. Timber is only subject to fungal attack when it is subjected to high levels of moisture and water for prolonged periods. The building facades and cladding systems are designed to ensure that the structural timber remains fully shielded from rain and other adverse weather conditions. Additionally, as much of the structural timber is open and visible inside the building, any ingress of moisture that has inadvertently penetrated the building envelope will be easily detected and the building envelope ingress problem can be repaired before any decay problems initiate.
In areas or designs where the engineered timber structural members may be concealed the structural members will be pre-treated to a standard required to prevent fungal decay that may result from inadvertent prolonged contact with water.
| ||Is the build system open plan and flexible enough to cope with multiple use and tenant changes?|
A specific advantage of the post-tensioned timber structural system is that it enables very long spans and large grid spacing to be easily designed and specified. This was previously unachievable with timber constructions and as a result a large number of load bearing walls were typically required. Using the EXPAN with Pres-Lam system, engineered timber buildings with grid spacing comparable to reinforced concrete and steel are a very real option. Open plan buildings can be fitted out internally with “temporary” infill timber framed non-load bearing walls and barriers as specific use requires and this ensures the floor plates remain flexible for future use changes.
Does it have a modern, light, open, warm appeal to it?
Timber as a construction material is timeless. It has a warm attractive aesthetic appeal universally liked. Large section engineered timber (LVL or Glulam) members that form the structural components of an EXPAN building form an attractive overall appearance and give the occupants a genuine sense and perception of robustness and strength.
Why is this better than similar reinforced concrete or steel office and retail buildings?
Simply put the new technology post-tensioned engineered timber building can match the equivalent reinforced concrete or steel building in achieving required structural strength and general amenity but in addition to this it offers:
Lighter weight construction that simplifies design and reduces foundation costs for multi-storey buildings situated on difficult soil conditions.A strength without weight structure that minimises acceleration loads caused by ground shaking.A construction system that has damage avoidance and construction simplicity central to its philosophy.The natural beauty and visual appeal of exposed timber.An environmentally sound choice that enables carbon neutral building constructions to be easily achieved.
But it's multi-storey timber....am I swapping an earthquake risk for a fire hazard risk?
Fire safety has been a crucial component of the EXPAN research programme, with the objective of providing owners and users of large timber buildings with confidence about personal safety and property protection. Despite the fact that all wood can burn, there are ways to imbue large timber buildings with very high levels of fire protection.
Fire resistance is essential in all multi-storey buildings, to prevent the spread of the fire to upper floors and to thereby help prevent structural collapse.
Large timber members, such as post-tensioned beams, columns and walls (such as those within EXPANs Structural Timber Solution) have excellent fire resistance because of their large member sizes and the predictable rate of charring. The level of fire resistance can be calculated using standard charring rates for AS 1720 or NZS 3603.
Floors in multi-storey timber buildings must meet two fire resistance requirements of containment and stability, in order to prevent fire spread and to ensure load-carrying capacity.
The fire resistance of timber floors has been established by calculation, backed up by full-scale fire testing. The fire resistance can be enhanced with additional layers such as concrete toppings or suspended ceilings.
Could I relocate some or all of the buildings in a few years time?
Another attractive benefit of the post-tensioned timber construction system is its ability to be easily deconstructed, relocated and reconstructed. It is therefore quite conceivable that a low-rise multi-storey building constructed within a CBD precinct could be subsequently deconstructed, transported to a new site and reconstructed some years after its original construction. An example of this to date is the EXPAN building located on Engineering Road at Canterbury University. This structure was originally built inside the university laboratory and was used for seismic and other testing for 1 year. It was subsequently deconstructed and reconstructed in its current location on campus.
Can a couple of additional storeys be added in the future?
The system is very modular and the large structural elements are all pre-fabricated off-site. This coupled with the lightweight of the engineered timber means that it is very easy to design and add additional storeys in the future, provided it does not exceed the design limit of the original foundation system.
Is it rapid to construct – how quickly can I get tenants or my own organisation in there?
The post-tension construction system provides for a very rapid construction sequence. Construction times are reduced due to the following:
All large structural elements are pre-fabricated off-site. This means earthworks and foundation placement can be happening whilst structural members are pre-fabricated elsewhere.The structural elements are all held together by post-tensioned tendons or bars running through hollow beams and walls. This means the structure is erected very rapidly as there is no requirement for large numbers of conventional nails and other wood fasteners to be applied on site.Minimal temporary bracing and propping is required as the construction sequence progresses, reducing overall construction time and cost.
Collectively these attributes enable a rapid construction time which means the building can be available to lease or for occupation in the shortest possible time.