New Zealand Is home to a new generation of prefabs. What does PrefabNZ CEO Pamela Bell see as the case for prefabrication on New Zealand construction projects?
Prefabrication, or prefab for short, refers to any part of a building that is made at a different location than the final building site, which is why it is also referred to as off-site construction.
What is prefab?
Off-site construction occurs in a manufacturing plant specifically designed for this type of process. Individual components, panels, modules or the complete building are constructed in the factory and then transported to the site. Once on site, the building will be installed onto a permanent foundation by fastening it to the ground and to other modules and covering and sealing the seams. These buildings meet the applicable building codes and are indistinguishable from traditional site-built construction techniques.
Prefab can also be used as a complementary system to traditional construction. It comes in all shapes and sizes, from small components such as prenailed wall frames, to panels (2D), larger modules (3D volumes) or even complete buildings. Hybrid prefab is a mixture of several prefab systems or prefab with traditional construction. Prefab can be any combination of timber, concrete, metal or plastic.
It can be used for a variety of purposes including residential, educational, healthcare and commercial applications. Buildings can range from a few modular units to several hundred. They can be arranged in architecturally pleasing configurations and can be many storeys high.
Prefab has a role in productivity
Prefab has a key role to play in improving industry efficiency, effectiveness and productivity in the design and construction process.
PrefabNZ is building on an innovative and rich history of prefabrication in New Zealand – from large-scale government investment in infrastructure projects (such as hydroelectric scheme housing) to some of the first one-piece fibreglass bathrooms (from Industrialised Building Systems in the 1970s). Interest in prefabrication has been renewed through the sustainability agenda and ‘off-site movement’ around the world. New Zealand is home to a new generation of prefabs such as bachkit, port-a-bach, HABODE, iPAD, K Bach and others.
A lot is happening in the prefab world, but it often happens in isolation and there is a need to coordinate, inform and in many cases, re-educate. The time is right to collaborate and market the benefits to the world.
Until recently, off-site fabrication, particularly in housing, has, rightly or wrongly, been associated with poor quality, a reduction in flexibility and choice, and higher costs. Market resistance prevented significant uptake of the technology, despite examples here and abroad that illustrate its technical feasibility and benefits.
But what are the societal and sustainability impacts of prefab construction methods?
REDUCED LOCAL IMPACTS
A key feature of prefab is that much of the process is in controlled factory conditions. This reduces the amount of time spent on site, which leads to reduced local impacts.
Experience shows that prefab hotel rooms can be assembled on site and completed ready to use in less than half the time of a traditionally built hotel of a similar size. This means that the site is disrupted for a shorter period, reducing noise, pollution and local traffic disruption. The lightweight nature of the construction also offers potential for smaller foundations and therefore less groundworks, again reducing disruption when bringing in concrete and removing spoil.
However, large deliveries of volumetric or panel units can be disruptive to the area and need careful logistics management to avoid problems.
Financially, the shorter construction period provides a quicker return on investment for the client and reduces overheads.
BETTER QUALITY AND REDUCED DEFECTS
In other industries, such as car manufacture and electronics, we expect zero faults when we purchase goods, yet defects in buildings are common at handover and are often costly and time consuming to rectify.
A construction site exposed to the elements doesn’t provide ideal conditions for high-quality workmanship and doesn't provide attractive working conditions in winter.
Factory-based activities allow better and safer working conditions and are more likely to lead to higher quality. It is easier in a factory to set up quality control procedures, with testing, prototyping and checking, for example, electrical and water installations in volumetric units can be tested prior to leaving the factory.
Feedback suggests that far fewer call backs are necessary to correct defects after completion of buildings using prefabrication. This is a significant cost and efficiency benefit to the builder and leads to satisfied customers. It also improves efficiency in the use of resources and reduces waste.
LESS WASTE IN MANUFACTURE
Construction waste is one of the principal waste streams to landfill sites. Factory manufacturing allows better management of the waste stream, more efficient use of materials, more accurate ordering and better storage conditions.
Any waste in a factory is easier to collect and reuse or recycle. Many prefab manufacturers have recycling facilities installed so that waste is sent back to their source for recycling, reducing the costs of waste disposal. There is further potential for reducing waste if the designer is prepared to use standard sizes, which can reduce the number and size of off-cuts.
Assembly of prefabricated components on site generates little waste, as the components arrive on site pre-engineered and ready to assemble together.
ENHANCED HEALTH AND SAFETY
On-site construction work can be dangerous. Off-site manufacturing allows much of the process to be carried out in more controlled and comfortable factory conditions where safety requirements can be more easily met and policed.
The use of scaffolding on site is a particular concern, and some off-site manufacturing schemes try to eliminate the need for scaffolding by integrating claddings during manufacture in the factory.
Conversely, the use of heavy lifting equipment to locate the prefabricated components on site requires careful management.
IMPROVED ENVIRONMENTAL PERFORMANCE
A building’s thermal and acoustic performance depends on the quality of workmanship and supervision. For instance, it’s important to correctly install insulation and ensure airtightness to ensure the building’s environmental performance once it is in use.
Reports from North America show higher thermal performance in homes that use off-site manufacturing techniques.
Factory manufacturing also allows workers to be better trained and supervised and allows regular checking and testing of performance.
A job manufacturing prefab components is generally more stable and long-term than site-based employment, so employers are often willing to invest in workforce training. Off-site fabrication requires a highly skilled and flexible workforce to be efficient, which necessitates greater training by employers.
Building sites are temporary employment locations, so they generally offer little long-term amenities for the local community. Factories, on the other hand, are often closely linked to the community, with much of the workforce living locally. They provide a long-term economic and often social service to the community.
Building sites are notoriously inefficient in their use of labour and materials. Studies in the United Kingdom found that site labour can be up to 50% less efficient than factory-based activities.
Volumetric construction using prefabricated modules also allows buildings to be dismantled and the modules reused at a different location.
Prefabrication generally leads to fewer site deliveries when compared to traditional construction methods.
Recent monitoring at a modular site suggests that deliveries were reduced by up to 90% when compared to a nearby site constructing a similar building using traditional techniques. However, these are generally large vehicle deliveries often travelling considerable distances from the factory.
Prefab construction also requires less on-site labour for a shorter period of time, so a well managed site using prefab should significantly reduce the amount of traffic it generates.
Opportunity for improvements
Prefabrication offers an opportunity to improve both efficiency and sustainability. However, many of the benefits are not yet fully realised, and the industry has much to learn to fulfil the potential of this technology.
Much work is needed as prefab is often still perceived as a project innovation rather than industry best practice.
Research by Pamela Bell for her Master of Architecture thesis, Kiwi prefab: prefabricated housing in New Zealand, has been used in this article.
Articles are correct at the time of publication but may have since become outdated.