Classification of mmc
The first of the five categories that MMC's can be defined by is Volumetric Construction. This system is one of the most widely known forms of MMC and is often referred to as modular construction. It consists of factory produced, three dimensional, and fully fitted units. These units are manufactured within a specially designed facility, with all required services such as water and service goods installed before transportation to the site. Once the unit has been transported onto site, it is lifted onto prepared foundations forming the dwelling, with two or more units being used to construct more complex designs. (NHBC Foundation, 2006, p.5)
This system is commonly deployed in the form of 'Pods', these are a type of volumetric construction and are commonly used within construction of hotels and student accommodation to form the kitchens or bathrooms. This is because of the high volume of services within kitchens and bathrooms and the repetitive nature of the design. The pods, usually non-structural and used within load bearing frames, and other types of volumetric construction can be constructed of a variety of materials such as, steel, timber, concrete and composites. (Parliamentary Office of Science and Technology, 2003, p.1)
This system lends itself well to situations where economics of scale can be achieved (NHBC Foundation, 2006, p.5), as the units can be factory prepared in a similar way to the methods of car production on a factory line; this system does have its drawbacks however, which will be discussed in depth in chapter 3.
The second type of MMC is the Panellised Construction System. This is a flat panel that is constructed in a factory and then assembled on site to form the three-dimensional structure. Alternatively the panels can be used in conjunction within other systems and designed to fit within an existing structure. The units can be in the form of roof, wall and floor panels and made from a wide variety of materials such as timber, steel and concrete. (Parliamentary Office of Science and Technology, 2003, p.1 and Venables, 2004, p.14)
There are numerous variations of the Panellised Construction System, these panels include; open, closed, concrete, composite, structural insulated (SIPS), infill and curtain walling. The main differences between these types of panels are the level of factory completion, the load bearing properties and their location within the construction (internally or externally). Panellised systems are more applicable to projects with variation within the design than volumetric systems as there is less standard repetition. (NHBC Foundation, 2006, p.7)
Hybrid Construction is another means by which MMC's can be categorised. As the name suggests this system uses a mix of both Panelised and volumetric methods within the same construction. Often, highly serviced areas such as bathroom and kitchens will be constructed using volumetric pods with the remaining part of the construction made up of types of the panelised system. (Venables, 2004, p.14)
Another means by which MMC's can be categorised is as Sub-assemblies and Components, these are larger components that can be incorporated into MMC or conventionally built dwellings. An example of these methods would be pre-fabricated foundations; these consist of prefabricated ground beams that are assembled with other components to form foundations. Sub-assemblies and components also consist of other large components used in housing, such as chimney stacks, roof structures and pre-fabricated dormers. (NHBC Foundation, 2006, p.10)
Site-based modern methods of construction, as discussed in Chapter 1, are also a form of MMC. These can include a wide variety of methods an example of which would be Aircrete; these are aerated concrete products that used to form major elements such as walls, floors or roofs (Venables, 2004, p.14). By definition however, this category can include a wide range of materials and techniques. This can make calculating the true usage challenging as many of the practices may not be considered innovative or modern by the users of the methods or materials.