THE DEVELOPMENT OF OFFSITE-SPECIFIC AUSTRALIAN CODES + GUIDELINES IS A NECESSITY IF PREFABRICATED BUILDINGS ARE TO SOLVE THE SAFETY + QUALITY CHALLENGE, WRITES PROFESSOR TUAN NGO, PROFESSOR AND RESEARCH DIRECTOR OF ARC CENTRE FOR ADVANCED MANUFACTURING OF PREFABRICATED HOUSING
Building defects are of great concern for building managers and owners. A study by Josephson and Hammarlund (1999) found that 32 per cent of the defects come from the design phase, around 45 per cent from site construction and almost 20 per cent from materials and equipment. Recently, Equity Economics in collaboration with Construction, Forestry, Maritime, Mining and Energy Union (CFMEU) analysed the added costs to asset managers/owners for remediating fire safety issues, water leaks, defects in structure, and cladding and associated costs in residential buildings constructed in the last decade.
It was reported that 3,400 apartment buildings across Australia had defective, non-compliant combustible cladding installed, (The Urban Developer, 2 November 2019) and would require remediation work to make the buildings safe. The total cost is estimated at up to 6.2 billion dollars in repair and remediation.
“It was reported that 3,400 apartment buildings across Australia had defective, non-compliant combustible cladding installed, (The Urban Developer, 2 November 2019) and would require remediation work to make the buildings safe. The total cost is estimated at up to 6.2 billion dollars in repair and remediation.”Professor Tuan Ngo, Professor and Research Director, CAMP.H.
Another study by Dr Nicole Johnston and Sacha Reid (2019) analysed the data of the audit reports of 212 inspected buildings located in three different states in Australia Queensland, New South Wales, and Victoria. The breakdown of the various defects in the inspected buildings indicates that water ingress to the buildings was the major defect, at 29 per cent of all defects. The ingress of water to the reinforced concrete and steel structures can cause serious problems due to the initiation and the progress of the corrosion process, which can result in the deterioration and the degradation to such structures before their service lives are completed. The defects in the safety system (fire protection, structural systems) of the buildings were found to be very high; 20 per cent, along with multiple contributors which were 22 per cent. In addition, building damages that occur during construction and can affect the serviceability of buildings were found to be 15 per cent as per the records.
Offsite construction and prefabrication can potentially minimise building defects. Ease of installation, reduced site work, product quality control and the safety improvement outcomes of prefabricated buildings are the key benefits which have been showcased in many projects. In conventional construction, there are a number of safety issues including working at height, congestion, severe weather work place accidents, neighbouring construction operations, etc. However, these problems can be reduced by about 80 per cent to 85 per cent, in prefabricated construction, as the majority of construction works, about 80 per cent, occurs in factories. Offsite construction provides consistent products, manufactured using repetitive processes, and typically undertaken with automation. Prefabricated construction systems also provide the benefit of high-quality control and less construction waste. This is because 80 per cent of construction operations take place in a factory, where building components can be tested before site installation.
The adoption of offsite construction in Australia is still facing challenges. To ensure building safety, structural performance and the strength of the structural and non-structural elements and their connections used in the prefabricated construction system are essential. Many prefabricated systems have been developed under commercial and confidential conditions. Designers rely on the strength of the structural and non-structural elements and their connections specified by manufacturers based on commercial-in-confidence testing.
In Australia, most of these tests were based on international standards such as ASTM and European standards. This is because, in Australia, there are no specific testing standards for most prefabricated structural and non-structural elements. Moreover, prefabricated structural design follows conventional structural design standards. Prefabricated structural systems are complex, non-conventional systems, however, and they use a range of non-conventional connections. Therefore, Australian design codes and guidelines need to be developed to include the design specifications and recommendations for prefabricated structures.■