Manufactured, Modular, and Prefab Homes

What is a Prefab House, Exactly?

The word prefab (also spelled pre-fab) is often used to describe any type of home that is made from easy-to-assemble building parts that were manufactured off-site. Prefab is an abbreviation for prefabricated and may be stamped on plans as PREFAB. Many people consider manufactured homes and modular homes as types of prefab housing. The ornate facades of 19th century cast iron architecture was prefabricated, cast in molds offsite and transported to the building site to be hung onto a frame.

Definition of Prefabrication

"The manufacture of whole buildings or components in a factory or casting yard for transportation to the site."— The Penguin Dictionary of Architecture, 1980, p. 253

Other Names Used for Prefab Houses

• factory-built
• factory-made
• pre-cut
• panelized
• manufactured
• modular
• mobile home
• industrialized building

Historic prefab structures include Sears Houses, Lustron Houses, and Katrina Cottages.

What is a Manufactured Home?

A manufactured home is a structure that is constructed almost entirely in a factory and rests on a permanent chassis. The house is placed on a steel chassis (a supporting frame) and transported to the building site. The wheels can be removed but the chassis stays in place.

A manufactured home can come in many different sizes and shapes. It may be a simple one-story "mobile home," or it can be so large and complex that you might not guess that it was constructed off site.

Local building codes do not apply to manufactured homes. Instead, these houses are built according to specialized guidelines and codes for manufactured housing. In the United States, HUD (the US Department of Housing and Urban Development) regulates manufactured housing through the HUD Code instead of local building codes. Manufactured homes are not permitted in some communities.

Other Names for Manufactured Houses

• factory-built
• factory-made
• mobile

Factory-Built Advantage

A manufactured home is one type of factory-built housing. Other types of prefabricated homes that use factory-made building parts include modular homes, panelized homes, mobile homes, and pre-cut homes homes. Factory-built houses usually cost much less than stick-built homes that are site-built.

Chassis Support System

"Manufactured homes are constructed on a chassis consisting of main steel beams and cross members; fitted axles, leaf springs, and wheels making up the running gear; and a steel hitch assembly. After the home is sited, the chassis frame distributes the manufactured home loads to the foundation system. The hitch assembly is generally removed for appearance purposes."— FEMA P-85, Protecting Manufactured Homes from Floods and Other Hazards (2009) Chapter 2

For more information about the HUD Code, see General Program Information and Office of Manufactured Housing Programs on the website of U.S. Department of Housing and Urban Development (HUD).

What is a Modular Home?

A modular home is constructed of pre-made parts and unit modules that are assembled together on site. A complete kitchen and bath may be pre-set in a house module. Modules may come with baseboard heating ready to attach to a furnace. Modules are often pre-wired with switches and outlets already in place.  Wall panels, trusses, and other pre-fabricated house parts are transported on a flatbed truck from the factory to the building site. You may even see an entire half-house moving along the highway. At the building site, these house sections are lifted onto the foundation where they are permanently anchored to a foundation already in place. Innovation in prefabricated construction is a trend of the 21st century. For example, the Northern California-based Blu Homes process includes using steel framing that literally allows a house to unfold on site.

The term modular home describes the construction method, or the process of how the structure was built.

" modular construction 1. Construction in which a selected unit or module, such as a box or other subcomponent, is used repeatedly in the aggregate construction. 2. A system of construction employing large, prefabricated, mass-produced, partially preassembled sections or modules which are subsequently put together in the field."— Dictionary of Architecture and Construction, Cyril M. Harris, ed., McGraw- Hill, 1975, p. 219

Other Names for Modular Homes

• factory-built house
• panelized home
• prefab or pre-fab
• systems-built home

Modular versus Manufactured Home

Are modular homes the same as manufactured homes? Not technically, for two basic reasons.

1. Modular homes are factory-built, but, unlike manufactured homes, they do not rest on steel chassis. Instead, modular homes are assembled on fixed foundations. A manufactured home, by definition, is attached to a permanent chassis. A manufactured home is sometimes called a "mobile home."

2. Modular homes must conform to the building codes for the locations where they are erected. Manufactured homes are entirely regulated by the US Department of Housing and Urban Development (HUD), Office of Manufactured Housing Program.

Types of Modular Homes

Some housing subdivisions prohibit modular homes because of the various types of prefabricated wall systems that are often put into place by using heavy equipment.

• A panelized home is a modular home assembled with pre-made wall panels.
• A log modular home may have one or several pre-made modules.
• Structural insulated panels (SIPs) and insulating concrete forms (ICFs) are types of modules in systems-built homes.

Pros and Cons

Buying a modular home can be deceptively simple. Although the modules may be "ready" for electric, plumbing, and heating, those systems are not included in the price. Neither is the land. These are the "price shocks" that all new home buyers must face.  It's similar to buying a vacation package without figuring in transportation costs. Look at the whole package, along with these perceived advantages and disadvantages:

Advantages
Money and time. Modular homes usually cost less to construct than stick-built homes. For this reason, modular homes are popular choices in budget-conscious neighborhoods. Also, contractors can assemble modular homes quickly—in a matter of days and weeks instead of months—so modular homes are often used for emergency housing after disasters. Kit homes such as Katrina Cottages may be described as modular homes.

Disadvantages
.Perceived negatives include inferior quality and lost resale value. Although there is no evidence to support either perception, these beliefs are persistent.

Examples of Modular Design

• The 1960s was a decade of great experimentation in modular design, including French modular vacation homes from 1969. The Japanese Metabolism Movement influenced its popularity around the world.
• Because of cost and time, modular homes become very popular after natural disasters; Lowe's teamed with designer Marianne Cusato to create this first of its kind Katrina Cottage located in Ocean Springs, Mississippi.
• In 1967, a young architect named Moshe Safdie was the talk of Montreal, Canada when he designed a new kind of housing development he called Habitat 67 using concrete boxes.
• Pritzker Laureate Shigeru Ban used 148 steel shipping containers and recycled paper tubes to create a 45,000 square-foot temporary museum. Called Nomadic Museum, it could easily be disassembled, transported to another venue, and reassembled.

The New Faces of Prefab Housing

Prefab houses are not new to the 21st century. The Industrial Revolution and the rise of the factory assembly line gave impetus to the idea that every hard-working family could own their own home—a belief that exists today.

Architect Michelle Kaufmann has been called the Queen of Green Prefab. After working in Frank Gehry's California studio, she began what she calls her "humble attempt" at saving the world with sustainable architecture. Her first attempt, Glidehouse, her own 2004 home in Novato, California, was chosen as one of the 10 Homes that Changed America on PBS. In 2009, she sold her mkDesigns to Blu Homes, a Northern California innovator of steel framed prefab structures that are built in a factory and "unfolded" on the construction site. At 640 square feet, the Lotus Mini, after a design by Kaufmann, is Blu Homes' entry into the Tiny House movement. How small can prefabs go? Check out Renzo Piano's 81 square foot "minimalist, single-occupancy living unit" called Diogene.

Sources

• Blu Homes Acquires Assets of mkDesigns, Home Designs by Green Prefab Pioneer Michelle Kaufmann, press release [accessed May 14, 206]
• Additional Getty Images from Mario Tama/Getty Images News Collection; Keystone/Hulton Archive Collection; and Archive Photos/Archive Photos Collection. Addition photo of Lowe's Katrina Cottage from PRNewsFoto/Lowe's Companies, Inc.