Prefab construction, the “next big thing” for decades, is finally moving into the mainstream.
Prefab construction refers to a variety of methods of building structures, including kit buildings shipped complete by truck or rail, “flat-pack” buildings that are basically pre-built wall and ceiling panels, and modular construction, which may be pre-built rooms or even entire homes. All employ the efficiencies of mass production to build structures faster, cheaper, and with less waste.
When combined with standardized design and components, prefab construction offers demonstrable savings in time and money. More consistent quality control is another advantage. The factory environment offers consistent conditions, a consistent team on site, and tightly controlled delivery of materials and production. Not coincidentally, most other industries that can benefit from mass production have adopted it already.
When combined with stock or semi-custom designs, prefab construction’s potential for cost savings and time savings really jumps. Repeatable designs are more efficient in regard to time, labor, and materials; they’re predictable compared to custom designs.
Project Frog relies heavily on standardized design to reduce cost and cut production time. The firm designs and fabricates components for buildings for the school, health care, government, and retail markets. According to the company, standardization of space designs and components means that designers can optimize the roofing or wall design, for example, to reduce the number of individual components, time, and steps required for assembly. Design standardization also lets builders become familiar with the component parts of every individual design, increasing the efficiency of construction.
Prefab construction also streamlines the installation process for wiring, lighting, and plumbing. When these component are installed at the factory, fewer subcontractors are need at the construction site, lowering costs by avoiding having to pay for their profit margins, while speeding up completion time.
The factory environment lends itself to higher quality buildings, said Steve Glenn of Living Homes, a builder in Santa Monica, California.
“It’s a controlled environment, so no weather issues. You can use jigs to precisely make sure your corners are true, and absolutely flat floors and ceilings,” he said. “It’s easier to have a more sophisticated QA process, so you get higher quality homes.”
Factory-built structures also can lessen waste. According to Living Homes, only about two per cent of their delivered materials end up as waste. That compares to thirty to forty per cent in a typical home build.
In addition, factory-built homes can be built simultaneously with sitework and foundation, rather than sequentially, saving more time.
Living Homes builds modules that are delivered to the site via truck. The crew fits the modules together with a crane. This process is fast — often a home can be assembled on site in just hours.
Project Frog takes a different approach. They build wall and ceiling assemblies that are shipped to the job site flat and stacked. The contractor then assembles the walls and ceiling piece-by-piece on their choice of foundation. Some assemblies, such as lighting, are pre-installed at the factory, which saves time on site as the need for subcontractors may be reduced or eliminated.
Custom designs can be made just as energy efficient as standard designs, but the modeling takes time and money as each project requires many hours of modeling. In contrast, a standard design is a known entity, and will provide predictable performance each time it is built. Modeling can take into account any changes to the stock plan, as well as individual site characteristics.
Project Frog claims its approach, which balances standardization with customization, lowers costs for construction by 30 per cent, can be built 30 per cent faster than a conventional building, and can reduce energy use by 50 to 60 per cent compared to a conventional structure.
Living Homes cites a 20 to 40 per cent cost advantage over a comparable stick-built home. Both companies build LEED-certified homes.