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Modular buildings and modular homes are sectional prefabricated buildings, or houses, that consist of multiple sections called modules. "Modular" is a method of construction (v. "stick-built" and other methods such as off-site construction. The modules are six sided boxes constructed in a remote facility, then delivered to their intended site of use. Using a crane, the modules are set onto the building's foundation and joined together to make a single building. The modules can be placed side-by-side, end-to-end, or stacked, allowing a wide variety of configurations and styles in the building layout.
Modular buildings, also called prefabricated buildings, differ from mobile homes, which are also called manufactured homes, in two ways. First, modular homes do not have axles or a frame, meaning that they are typically transported to their site by means of flat-bed trucks. Secondly, modular buildings must conform to all local building codes for their proposed use, while mobile homes, made in the United States, are required to conform to federal codes governed by HUD (U.S. Department of Housing and Urban Development). There are some residential modular buildings that are built on a steel frame (referred to as on-frame modular) that do meet local building codes and are considered modular homes, rather than mobile homes. 
Modular buildings may be used for long-term, temporary or permanent facilities, such as construction camps, schools and classrooms, civilian and military housing, and industrial facilities. Modular buildings are used in remote and rural areas where conventional construction may not be reasonable or possible, for example, the Halley VI accommodation pods used for a BAS Antarctic expedition. Other uses have included churches, health care facilities, sales and retail offices, fast food restaurants and cruise ship construction.
Modular components are typically constructed indoors on assembly lines. Independent building inspectors are on site to supervise the construction and ensure that the company adheres to all building codes during assembly. Modules' construction may take as little as ten days but more often one to three months. Completed modules are transported to the building site and assembled by a crane. Placement of the modules may take from several hours to several days. Once assembled, modular buildings are essentially indistinguishable from typical site-built structures. While mobile manufactured buildings often decrease in value over time, a well-built modular building should retain value similarly to site-built structures.
Modular buildings are often priced lower than their site-built counterparts, for a variety of reasons. Manufacturers cite the following reasons for the typically lower cost/price of these dwellings:
Whilst there are many advantages to all forms of modular buildings, there can be limitations also.
Some home buyers and some lending institutions resist consideration of modular homes as equivalent in value to site-built homes. While the homes themselves may be of equivalent quality, entrenched zoning regulations and psychological marketplace factors may create hurdles for buyers or builders of modular homes and should be considered as part of the decision-making process when exploring this type of home as a living and/or investment option. In the UK and Australia, modular homes have become accepted in some regional areas; however, they are not commonly built in major cities. Recent innovations allow modular buildings to be indistinguishable from site-built structures.
Differences include the building codes that govern the construction, types of material used and how they are appraised by banks for lending purposes. The codes that govern the construction of modular homes are exactly the same codes that govern the construction of site-constructed homes. In the United States, all modular homes are constructed according to the International Building Code (IBC), IRC, BOCA or the code that has been adopted by the local jurisdiction.
The materials used in modular homes are the same as site constructed homes. Wood-frame floors, walls and roof are the most typical. Some modular homes include brick or stone exteriors, granite counters and steeply pitched roofs. All modulars are designed to sit on a perimeter foundation or basement. In contrast, mobile homes are constructed with a steel chassis that is integral to the integrity of the floor system. Mobile homes often require special lenders. Most companies have standard plans. However, all modular buildings can be custom built to a client's specifications. Today's designs include multi-story units, multi-family units and entire apartment complexes. The negative stereotype commonly associated with mobile homes has prompted some manufacturers to start using the term "off-site construction." 
Typically, modular dwellings are built to local, state or council code, resulting in dwellings from a given manufacturing facility having differing construction standards depending on the final destination of the modules. For example, homes built for final assembly in a hurricane-prone area may include additional bracing to meet local building codes. Steel and/or wood framing are common options for building a modular home.
Some US courts have ruled that zoning restrictions applicable to mobile homes do not apply to modular homes since modular homes are designed to have a permanent foundation. Additionally, in the US, valuation differences between modular homes and site-built homes are often negligible in real estate appraisal practice; modular homes can, in some market areas, (depending on local appraisal practices per Uniform Standards of Professional Appraisal Practice) be evaluated the same way as site-built dwellings of similar quality. In Australia, manufactured home parks are governed by additional legislation that does not apply to permanent modular homes. Possible developments in equivalence between modular and site-built housing types for the purposes of real estate appraisals, financing and zoning may increase the sales of modular homes over time.
According to manufacturers, modular homes are designed to be stronger than traditional homes by, for example, replacing nails with screws, adding glue to joints, and using 10-20% more lumber than conventional housing. This is to help the modules maintain their structural integrity as they are transported on trucks to the construction site; however, it is difficult to predict the final building strength since the modules need to endure transportation stresses that traditional homes never experience.
When FEMA studied the destruction wrought by Hurricane Andrew in Dade County Florida, they concluded that modular and masonry homes fared best compared to other construction.
The CE mark is a construction norm that guarantees the user of mechanical resistance and strength of the structure. It is a label given by European community empowered authorities for end-to-end process mastering and traceability.
All manufacturing operations are being monitored and recorded:
- This ID and all the details are recorded in a database dedicated to quality, - At any time, the producer has to be able to answer and provide all the information from each step of the production of a single unit, - The EC certification guaranties standards in terms of durability, resistance against wind and earthquakes.
Modular buildings can be assembled on top of multiple foundation surfaces, such as a crawl space, stilts (for areas that are prone to flooding), full basements or standard slab at grade. They can also be built to multi-story heights. Motels and other multi-family structures have been built using modular construction techniques. The height to which a modular structure can be built depends on jurisdiction, but a number of countries, especially in Asia, allow them to be built to 24 floors or more.
Exterior wall surfaces can be finalized in the plant production process or in the case of brick/stone veneers, field applications may be the builders' choice. Roof systems also can be applied in the field after the basic installation is completed.
Weather, population density, geographical distances, and local housing architecture play a role in the use of modular construction for home building. Because modular construction is so adaptable, it has begun to permeate every region of the country.
The northeast is populated with factories that can combine modular housing design with other construction methods such as panelization and SIPs. Modules are typically limited to 16' width and up to 70' lengths because of the narrow road structure and densely populated areas of the region. Other limitations are placed on transportation to locations such as Connecticut, Cape Cod, and Long Island.
The Mid-Atlantic region is similar to the northeast, in terms of building design and transport restriction to modules to a width of not more than 16'.
Manufacturers in the Southeast often limit their ability to customize homes and focus on very traditional single story floor plans. Much of the south is in coastal and high wind areas; modular construction may prove appealing in this area as it is already inherently stronger as it must be built for transport and craned installation, therefore offering wind resistance as good or higher than site-built construction.
The central plains states typically are made up of farming and rural communities. Ranch homes are the mainstay of the region. Prone to strong storms and tornado conditions, modular construction offers the ability to better withstand these storm patterns than its site built counterpart. The inter-module attachments that must be made when assembling a modular home on a foundation offer an inherently stronger home than site built construction can offer. Interior finishes on both the walls and ceilings are typically textured. Corners on interior walls are typically rounded and finish trim around windows is optional. Because of the wider road and lower population density, modules can be as wide as 20' and as long as 90'. The ability to provide larger modules reduces the amount of modules needed to complete a home.
Home design in this area ranges from Chalet style homes to log cabin style homes. Manufacturers in the region therefore provide a number of styles of homes. Capability varies from factory to factory as well as the ability to do complete customization of floor plans. Transportation is limited mostly to 16' wide modules to travel the roads of the area.
The high cost of living in coastal areas, and especially California, may provide modular construction an edge due to its lower cost. Extreme building regulation and environmental requirements can delay the start of residential construction. However, the speed of the actual construction process and cost efficiencies work to provide a home at great value. Several factories specialize in environmentally responsible construction by following green construction standards and offering zero energy homes.