Prefabrication and modern methods of construction: promise and trade-offs

Prefabricated and modular construction gets a lot of attention as a way to build faster and more consistently. Some of that attention is deserved, and some of it is hype. Here is a plain look at what the term covers, what the evidence says, and how we think about whether it fits a given project.

What it means

The Australian Building Codes Board (ABCB) uses the term modern methods of construction to describe "a range of construction methods that are different to traditional onsite construction". It covers:

• Prefabrication and off-site manufacturing: components such as wall frames, trusses, floor cassettes or bathroom pods made in a factory and assembled on site.
• Modular or volumetric construction: complete three-dimensional modules built off site, transported and joined on site.
• Emerging methods: for example robotics and 3D printing.

What the evidence claims

The ABCB cites external research suggesting that prefabricated construction can reduce the cost of homes by up to 20 per cent (attributed to the Productivity Commission) and be up to 50 per cent faster to construct than traditional methods. It also points to improved certainty, safety, quality and sustainability benefits.

These are "up to" figures from research, not guarantees, and they depend on the project type, the scale, and how well the process is planned. A single custom home will not necessarily see the savings that a repeatable project of many identical units might.

What is changing in regulation

The ABCB is working on a national voluntary certification scheme for manufacturers of prefabricated construction, and on nationally consistent definitions for the National Construction Code. It has also published handbooks for practitioners on prefabricated and modular construction, evidence of suitability, and performance solution processes. The aim is a more consistent national approach and fewer regulatory barriers. Because this is still developing, check the current position with your certifier.

What to weigh before choosing it

Here is how we think about whether prefabrication fits a project:

• Repeatability. The more repeated components, the stronger the case. Highly custom designs benefit less.
• Decisions have to be made earlier. Changing a component after it has been manufactured is difficult and expensive, so design has to be resolved up front.
• Site and logistics. Access, crane position, transport routes and lifting all need to work. Poor access can undo the savings.
• Approvals and certification. Someone has to demonstrate the components and connections comply. Ask what evidence of suitability is available and who is responsible for it.
• Site work does not disappear. Footings, services connections, weatherproofing of joins and finishes still happen on site, and they need the same level of supervision.
• Supply chain. Availability, lead times and the financial standing of the manufacturer matter.
• Quality control cuts both ways. Factory conditions can improve consistency, but defects repeated in a factory are repeated in every unit, so inspection before delivery is important.

How we approach it

We do not adopt a method because it is new. We look at whether it improves the outcome for a particular project once cost, programme, compliance, buildability and long-term performance are all considered, and we are open about the trade-offs. If prefabrication or another modern method could suit your project, get in touch and we can talk it through honestly.

Sources

• Prefabricated, modular and offsite construction, Australian Building Codes Board
• Prefab and modular construction in Australia, Housing Industry Association

This article is general information, not advice for your project. Suitability depends on the design, the site and the approvals, so confirm requirements with your certifier and designer. Full website disclaimer