Prefab houses (prefabricated houses) are specialised houses where the components are constructed off-site in standard sections to be assembled and finished on-site. As an alternative to traditional building techniques, this serves as a faster construction method with less waste and a less negative environmental footprint. Prefab houses can be referred to in many ways, including prefabricated homes, modular houses, and modular homes.
The Hong Kong construction industry, for example, generates waste up to 40% of the total landfill intakes, and prefab construction as an alternative is projected to reduce this waste by almost 85%. It is also a faster means of construction, as evidenced by a Chinese construction company, which erected a 57-storey structure in 19 days in 2015 using this method .
Due to the nature of the requirements for prefab houses, the materials used need to meet certain criteria, such as durability and lightweight. However, not every single element of a building needs to be considered for prefabrication. Only specific components that make up the bulk of a building’s construction and interior fittings can be prefabricated, such as walls, floors, roofs, closets, and shelving units.
In this article, you will learn about:
- What prefab houses are
- Materials used in prefab houses
- Future trends of prefab houses
What are prefab houses?
Prefab houses are houses of which the components have been constructed off-site before assembly/installation at their final location. The fabrication of these components is done in a controlled environment; most often, a factory. The driving principles behind prefab houses are :
1. Industrialization and mass production
Prefab homes can be mass-produced since the components can be constructed relatively faster than on-site building. This would represent a shift in the focus and infrastructure of building from producing raw materials such as cement, sand and I-beams, to producing modular components such as precast panels and plywood.
2. Speed and Affordability
Prefab homes are cheaper than regular homes due to the amount of time and effort saved compared to traditional construction. The time consumed is more often concentrated in making the components rather than in assembling them.
3. Customization and Sustainability
The design of prefab houses needs the components to fit in a way that allows for a reasonable degree of customizability. Furthermore, the processes employed in the construction and assembly need to have as little environmental impact as possible.
In a nutshell, the advantages of prefab homes include:
- relatively lower overall costs
- easier quality control
- faster and safer construction
- less wastage and value recovery via dismantling rather than demolition
The disadvantages centre on their reduced strength and stability, which is of serious concern in cases of natural disasters and even during the transportation of the prefab segments from the site of fabrication to the site of installation .
Materials used in prefab homes
Several materials are used in prefab homes, such as concrete, timber, and metals . Here, we examine some of these materials and their efficacy of use.
The use of concrete as a building material is already well documented. However, its use for prefab houses takes on a different dimension as other considerations are involved. It is possible to achieve sturdy structures with very intricate profiles through the use of moulds. Precast concrete panels can also be used in larger multi-storey constructions that can constitute the building blocks. The materials themselves can be formulated to meet certain requirements, such as lightweight (there are concrete formulations that can float on water) and resistance to temperature fluctuations. Additives such as graphene oxide can be added to concrete to make it a more sustainable material.
Wood is another commonly used material in prefab homes. It can be used as-is, in the form of “heavy timber”, which refers to column and beam structures, or in the form of “mass timber”, which refers to its use as panel systems (a combination of wood and other materials). Wood’s fire resistance is often a subject of concern, but wood systems can be designed to have good fire resistance due to the ablative char that forms during exposure to fire. Bamboo is a common building material that can be adapted for use in prefab homes, as well. Wood can also be engineered into composites that have good material properties, even comparable to steels. Examples of such wood materials include cross-laminated timber (CLT), glued laminated lumber (GLULAM), and laminated veneer lumber (LVL). They are all essentially several sections of wood sheets glued together in such a way that there are no continuous grain lines for fault/crack initiation or propagation.
Steel is a common building material used as support frames (I-beams and columns), floors, and walls for modular buildings. It may be used in conjunction with materials or as the bulk of the building materials, such as in the adaptation of shipping containers. Research suggests that steel housing structures can be built as high as ten storeys or even more.
Advantages of steel are its relatively low weight-to-strength ratio, ease of transportation, and recyclability. In contrast, its drawbacks include poor insulation, subpar acoustic performance, and the fact that using steel for this purpose potentially takes it out of the recycling loop.
Glass is a highly customisable material for several building functions. Several types of glass are used in construction, including tempered glass, laminated glass, heat-strengthened glass, and wire glass. Glass can bring about useful properties, such as high strength, insulation, chemical resistance, and fire resistance. Glass also has a unique aesthetic quality and is fully recyclable, a common theme of prefab houses.
Recycled and reclaimed materials
Recyclable materials include some of the traditional building materials, such as concrete, gypsum wallboard, and steel. They also include other materials, like cellulose insulation, ceiling tiles, plastics, ceramic or porcelain tiles, and fibreglass insulation. All these materials can be used to construct prefab homes.
The challenge of using these materials is that some of them do not have a steady supply and cannot be relied upon for consistent use. Some of these materials may also be toxic or harmful to residents over the long term and so must be carefully studied if they would fit the purpose.
Prefab houses contribution to sustainability
Modular prefabrication has been proven as a process of many sustainable benefits as compared to conventional approaches. Aside from the obvious aspects like waste reduction and lower on-site energy consumption, numerous factors play their roles in the sustainability of prefab houses, particularly in the construction phase. Its sustainable performance has been evident when it comes to dealing with issues of construction waste, aesthetic options, site disruption, water consumption, and pollution generation.
To properly evaluate the sustainability of prefab construction – and construction, in general – all the phases of constructing, operating, and maintaining a building throughout its life cycle should be considered.
A 2019 study on the sustainable performance of prefabricated modular buildings extracted 16 indicators across economic, social and environmental dimensions to compare with conventional building performances. The results showed that prefab construction had significantly less impact on the environment, especially in terms of emissions, energy, and water consumption. Prefab construction also exhibited economic advantages as it reduced the amount of steel, concrete and formwork used in traditional construction by 60%, 56% and 77%, respectively .
How additive manufacturing can help build prefab homes
Additive manufacturing (AM) has mostly been considered a technology limited to small products that are difficult to scale up for larger designs. Newer technologies are making breakthroughs not only in using AM for large-scale design but also in using it for construction.
The major challenge, however, is formulating a material that has properties suitable for 3D printing and that will result in a sturdy enough building. Cement-based materials, polymers, and metals are some of the materials that can be modified for additive manufacturing.
Construction via additive manufacturing can cut construction costs significantly as it generates less waste and is less labor-intensive. Some iconic buildings have already been built using AM technology, including an office building in Dubai, a bridge in Amsterdam, and a hotel building in Manila, among many others .
Future trends of prefab houses
Even though the entire idea of prefabricated buildings is still quite novel, there are exciting new possibilities in the industry. In terms of materials used, more materials are being considered, such as carbon fibres for making fibrous structures and special plastics used for 3D printing of large structures. In terms of execution, robotic technologies are being developed that can reduce human input to the minimum and complete construction off-site via data from computer programs such as Building Information Modelling (BIM) .
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