Prefab, Modular, Off-Site Construction- What’s the Difference?

For more information on the prefab evolution/revolution, check out this great series by Dwell Magazine.
For more information on the prefab evolution/revolution, check out this great series by Dwell Magazine.

As the world begins to search for new ways to be more energy efficient, buildings are always a big focus area.  It is believed that buildings in the US account for over 40% of energy use and represent the largest single end-use of energy and emitter of greenhouse gases. This isn’t new information. We’ve been covering it extensively in our posts on air sealing, net zero, building resilience and green building. Yet there is more to efficiency than just the energy required to live in a house, i.e. heating, cooling, lighting, power. Over the last decade, the lens has gradually shifted to include the construction phase; specifically how and where we build our homes.

Yes, we’re talking off-site construction. Or what some call prefab construction. The concept isn’t new. Due to recent advances in technology and consumer awareness, there is a growing acceptance of the environmental advantages of offsite, prefab, and modular building systems. However, when talking about different kinds of homes, there may be some confusion in regards to the terms used to discuss what kind of building is being made. Prefab, Modular, and Manufactured are sometimes mistakenly used interchangeably, but they all mean different things. Let’s break it down.

What is off-site construction?

Officially, according to The National Institute of Building Sciences [NIBS],

“Off-site construction is the planning, design, fabrication and assembly of building elements at a location other than their final installed location to support the rapid and efficient construction of a permanent structure.”   

Plainly speaking, the difference between off-site and onsite construction comes from where the building is built, not how.  

What is prefabricated housing?

If off-site is the where, then prefab is the how. Technically, any home that has sections of the structure built in a factory and then assembled on site can fall under the “prefab” designation. Prefab buildings of all kinds must adhere to state and federal building codes and undergo regular inspections, just like any site-built home. This ensures that prefabicated homes are at least as safe as their site-built counterparts, though there is evidence that a well-built modular home is even more sturdy than a similar site-built home.

ECHOtape Inline CTAWhat is modular?

Both Modular and Manufactured fall under the umbrella term of prefab, but just as boxers and pit bulls are both dogs, they are not the same. With modular construction, the building is constructed in separate box-like modules which are transported, then secured together on-site to form a whole. According to NIBS, the modular industry consists of two distinct segments: relocatable (temporary) modular and permanent modular. Re-locatable modular buildings are structures which meet temporary space needs, such as job site trailers, temporary classrooms, communication pods, and show rooms. Although permanent modular construction (PMC) has been flourishing for a decade or more in Europe, it is an emerging market in North America. PMC is comparable to site built structures meeting the International Building Code (IBC), the difference being that it is simply manufactured in chunks within a factory. Permanent modular is being used globally for multi-story multi-family structures, government buildings, hospitals and health care facilities, school and even hotels.

What is manufactured housing?

Lastly, manufactured homes are built in a factory like prefabs, however there is no construction that happens on site. Manufactured homes are constructed on a steel frame, shipped on its own wheels, and then laid on a crawl space, or a slab of concrete. In some cases, the wheels that got the house to the build site aren’t even removed, just covered up with side skirting.  Americans might better recognize the term “mobile homes,” however mobile manufactured homes have not been made since 1976.  This was the year HUD set forth new and safer construction and installation standards for all homes built in a factory.  Today, mobile homes may only be located inside a mobile home park or on an owner’s land, and unlike other prefabicated, modular homes which are considered real estate and so maintain or increase in value over time, manufactured homes are considered personal property and so lose value as soon as it’s driven off the lot, just like a car. Their value will continue to decrease for the full life of the home.

Here, at ECHOtape, we’re excited and intrigued by the advancements being made in off-site construction. It’s a topic we plan to discuss in depth during the coming months, so if there is something you would like to know, please email us at