Dovedale Student Accommodation used Stria James Hardie cladding product.
The offsite construction sector will need to plan carefully for the start-up phase of delivering 16,000 homes in the first three years, with the remainder thereafter. It is clear that a staged approach and learning on-the-job will enable ongoing improvements, much like a product development cycle with prototyping, tweaking, and evaluating before large-scale manufacture. We will need agile on-site techniques to embed offsite innovations, such as those demonstrated in the Dovedale project below.
“It is clear that a staged approach and learning on-the-job will enable ongoing improvements, much like a product development cycle with prototyping, tweaking, and evaluating before large-scale manufacture. We will need agile on-site techniques to embed offsite innovations.” Pamela Bell, PrefabNZ CEO.
In a broad industry context, there is large-scale work on industry transformation led by BRANZ, the country’s building research association that oversees spending of the research levy. The Industry Transformation Agenda (ITA) is a framework for the building and construction industry to work collectively to solve complex issues – such as skills shortages, boom and bust cycles and procurement issues – to enable a better built environment for New Zealanders.
NZ’s ITA has six priority areas, of which several apply to offsite construction:
- Adoption of new technologies,
- Shared learning through greater collaboration and continuous improvement,
- Better information flows to improve productivity,
- Developing nextgen people capability.
The ITA is based on the World Economic Forum’s ‘Shaping the Future of Construction’ report (2017) that identifies three levels of industry change, the level of the company, the sector and the government.
Panelised prefabrication has proven benefits over traditional building systems. Recent post-graduate research on 151 NZ construction projects has shown panels contribute to 21% cost savings, 47% time-savings and 10% productivity savings.
Wajiha Mohsin Shahzad’s, PhD Thesis from the University of Massey (2016) showed that factors affecting the level of prefab importance included building type, location, logistics, type of prefabrication, scale/repeatability, standardisation, contractor’s level of innovation, environmental impact, project leadership, type of procurement, whole of life quality, site conditions, site layout and client’s nature.
The University of Canterbury Dovedale Student Accommodation project was recently completed using offsite manufactured structural panels and bathroom pods. A range of tried and trusted plus new and innovative materials were used, including James Hardie’s Stria cladding board. According to Wade Macauley of Spanbild Projects Ltd (offsite project design and delivery) and Tony Whale of Concision (panel manufacturer):
The successful completion of panelised construction at University of Canterbury’s Dovedale Accommodation Project is a ground-breaking milestone for Spanbild and Concision in the commercial use of structural panelised manufacturing technology in New Zealand.
Five two-storeyed blocks contain 16 accommodation units and a total of 90 individual bedrooms, as well as kitchens, shared bathrooms, and several ensuites. Lead contractor, Naylor Love, committed to provide the student accommodation building within a 20-week construction window, in order to be ready for the start of the 2018 university year. This meant the use of offsite manufacturing was necessary in order to deliver accurately and efficiently on time.
Over 2,500 lineal metres of panelised floor, structural wall and roofing panels were manufactured offsite and assembled at site by Concision. The hybrid panel-and-pod process also included compressed timber ceilings by Metrapanel and 64 prefabricated bathroom pods by Construction Components. Wall assembly at site took just ten weeks from mid-August to end October, during several bouts of inclement weather.
Spanbild’s engineering team designed the structural panels which were then detailed by Concision, and manufactured in just 12 days. The staged process of on-site work, together with the learnings for further offsite improvements, mean that now the team forecasts a 7-10 week total programme for a similarly complex commercial development of this type and size!
The five separate accommodation blocks enabled learnings as the on-site team moved from one to another. Spanbild and Concision worked closely with contractor Naylor Love to confirm and advance current approaches, and identify new on-site learnings. According to Wade Macauley, “these will be invaluable for increasing speed and efficiency, reducing site congestion, decreasing site labour and subcontractor requirements, improving quality control, shortening schedules, and reducing cost still further on future large-scale commercial projects.”
Key on-site learnings according to the Spanbild / Concision team include:
- Offsite manufacturing changes the critical-path completely relative to a traditional build programme. Design for Manufacturing and Assembly (DfMA) is essential but is a radically different design process. Early integrated involvement with the overall design build team is essential to achieve the many benefits available over conventional build. Examples identified ranged from services accuracy, window and door opening details, and blocking requirements, to component clash detection, project sequencing, and integration with other subcontractor work.
- Work by other major subcontractors (eg. ground floor concrete slabs, bathroom pods, and roof components) should be integrated as closely as possible with the panelised DfMA team to avoid issues that otherwise only become apparent once all build components are on-site, when they immediately impact the critical path and can cause substantial re-work.
- An effective and robust weatherproof envelope is essential to achieve the benefits. Design detailing, and well-educated and experienced installation and subcontractor crews, who maintain the weatherproof envelope during construction, are critical.
- Services integration into panels significantly improves installation speed, reduces unnecessary sub-trade work or rework, and substantially reduces total project schedule.
- Ideally, a fully prefabricated and pre-clad roofing system would provide an improved waterproofed building envelope and reduced time of installation at site.
Material suppliers also enabled enhanced learning at site. James Hardie provided input with their Stria cladding system, an advanced lightweight cement composite cladding made using Portland cement, ground sand, cellulose fibre and water. They worked from the design stage with details to minimise waste and technically review jointing methods.
James Hardie showed other completed case study projects to the lead builders, as well as providing an installer to provide hands-on training and health-and-safety guidance on the first accommodation block. The cladding went up swiftly, with just 2 weeks per building once preparatory flashing work was complete.
Another important learning from this project was about inter-operability and the interface of different components, panels and pods at site, plus the coordination of the installers! This highlights a great opportunity to use more advanced Building Information Modelling or BIM for future projects.
While panelised manufacturing can be used for almost any building design and layout, there are simple ways to change designs from manufacturing unfriendly (limited benefits) to manufacturing friendly (significant benefits) to manufacturing optimised (major benefits for schedule, cost, efficiency, quality, etc). Including the DfMA team from building concept stage, with clear definition of scope, roles and responsibilities, allows these benefits to be captured without wasting time and cost on substantial redesign and rework later in the design process.
The Dovedale Project has demonstrated the major benefits for commercial developments of Concision’s structural panelised manufacturing. By replacing the traditional design/build process, and challenging every paradigm, the Spanbild/Concision team have created a new critical path for New Zealand commercial buildings that maximises many of the benefits of offsite manufacturing.
“The Dovedale Project has demonstrated the major benefits for commercial developments of Concision’s structural panelised manufacturing. By replacing the traditional design/build process, and challenging every paradigm, the Spanbild/Concision team have created a new critical path for New Zealand commercial buildings that maximises many of the benefits of offsite manufacturing.”
Pamela Bell, PrefabNZ CEO.■