There’s been a lot of buzz lately about prefab buildings. Yet there’s a great deal of mystery about what prefab is. As a young architect, I often wondered why buildings weren't built like automobiles, especially once I started seeing first-hand how time-consuming and expensive it was to create construction drawings. “Why do we build the same way we did 100 years ago and re-invent the wheel with every project?” I'd ask my bosses. They said I should be thankful that was the case since we’d be out of a job if it wasn’t. But being a pragmatist and an efficiency-seeker, I never gave up on the question.

Tract homes are the most common answer to this question. They allow a much reduced price over a custom home. Although providing affordable housing is imperative, cookie-cutter communities are not always very appealing. Most people have an appreciation for unique houses. Even more efficiently constructed than tract homes, manufactured or mobile homes are built in a factory utilizing an assembly-line approach with many automated processes. But again, this solution is not typically the American dream.

Prefabricated homes are different. It is true that many prefab homes are pre-designed and selected from a list of standard options, with several plan or façade alternatives to choose from. However, many are custom homes designed by an architect hired by a client. These structures are built within a factory very similar to how they would be built on-site. The trades are bid out, and the subcontractors are hired by the factory. However, the buildings must be designed and constructed in modules that are small enough to transport on truck beds to the jobsite. Typically 10 to 15 feet wide, these modules join together via a double wall or, where expansive spaces are needed, a beam. These modular buildings can be any style, modern or traditionally, but tend to lend themselves to a contemporary design.

Factory-built buildings, even custom-designed ones, are usually less expensive than those that are site-built, because factories are located where labor is cheap. The transportation cost to the site, however, can offset the savings if the site is too far away. The buildings are typically delivered to the site with the interiors already completely built-out, including kitchens and bathrooms, so once at the site, they can be completed within about a week. There is less waste produced when a building is factory-produced versus site-built.

In towns where the cost of construction is expensive, taking the prefab route may be the only way to afford a new custom home. In many parts of California, a site-constructed, average middle-class house runs about $300 per square foot. The same home built in a factory might cost about 25% less with the added environmental benefits of being more eco-friendly even with the transport factored in. Passing over the local contractors may be frowned upon, however. Of course, remodels, additions, and other specific types of projects are still better suited for on-site construction.

Multi-family residential buildings and commercial buildings can be prefabricated as well. I worked on several Bank of America branches that were prefabricated. This approach cut the construction schedule in half. These buildings were built in the factory in approximately six weeks while the site work, such as the foundation, paving, and utility hook-ups, were completed simultaneously. They were then transported, erected, and finished within two additional weeks.

Many prefab companies are really architectural firms, development companies, or dealers that have created a new brand and outsource the building fabrication to a factory Other prefab companies are true manufacturers, although they are not complete one-stop-shops since the site work must still be designed and permitted.