Subscribe to our newsletter to receive the latest news and events from TWI:

Subscribe >
Skip to content

What is a Modular Building? A Guide to Modular Construction


Modular buildings are structures that are constructed in a factory setting before being transported for assembly on site.

Despite having been used as a method of construction for decades, this type of modular structure is increasingly being used for a wider range of construction projects, ranging from offices and hospitality builds to residential properties, and more.

How are They Made?

Modular buildings are manufactured in sections away from construction sites before being delivered to the desired location where they are installed into a final building design. 60-90% of the work is completed in a factory-controlled environment, either as a complete structure or as modular subassemblies for a larger project.

This offsite construction allows the use of lean manufacturing techniques to create the prefabricated modules. These modular units can be placed end-to-end or stacked up to create different configurations. The modular construction process is completed onsite using inter-module connections (or inter-connections) to tie the units together.

Permanent modular buildings, such as prefabricated homes, are built to standards that are equal or higher than traditional site built properties, ensuring high levels of quality control.

Permanent modular construction (PMC) can be carried out with a variety of building materials, such as concrete, steel or wood, and can also include provision for adding windows, power supplies, water and sewage pipes, telecommunications, air conditioning and more. Many of these additional features can be installed before being taken to site, saving construction time later in the process. These PMC structures are designed to remain in one location once built and can include as many storeys as allowed by building regulations.

The design phase is particularly important in the creation of modular buildings. Design for Manufacture and Assembly (DfMA) practices need to be used to make sure the assembly tolerances are controlled and ensure any slack or misalignment can be taken up. CAD systems, additive manufacture (3D printing) and manufacturing control systems are important for modular construction since the components cannot easily be realigned onsite.


Modular buildings generally fall under one of two types - permanent or temporary. Within these types, the actual buildings can range from ‘flat-pack’ solutions to façade systems and those where much of the construction is completed offsite before being delivered and put together (see about ‘Volumetric Modular Construction,’ below).

Modular Building Construction

What is Meant by Modular Construction?

Modular construction is a process where a building is constructed offsite using controlled plant conditions before being transported and assembled at a final location. This type of construction can incorporate a range of different building types and floor plans.

When was Modular Construction Invented?

The first recorded instance of modular construction came in the 1830s, when a London carpenter called John Manning made a prefabricated home for his son. This home was made in parts before being shipped from England to Australia and assembled.

This construction method was also popular during the 1840s California Gold Rush in the United States, when it was used to build the ‘Crystal Palace for Britain’s Great Exhibition of 1851, and grew in popularity with the creation of prefab structures both during World War Two and for rapid rebuilding of homes following the end of the war. The popularity of modular construction in the U.S.A. has led to the creation of the Modular Building Institute.

What are Modular Units?

Modular units are the sections that are joined together to make a prefabricated building or house. The number of units required differs depending on the size and style of the finished project.

How Much Do They Cost?

The cost varies depending on scale of the project and the types of materials used.

Other factors, such as the inclusion of internal fittings and fixtures, can also impact the cost of a modular building. However, case studies show they can offer significant savings when compared to traditional construction. This is due to factors such as weather not being a problem in delaying a project schedule and the ability to work on the structure offsite while the site is being prepared, reducing construction industry lead-times for completion.

How Long Do They Last?

How long a modular building lasts depends on whether it has been designed to be temporary or permanent. However, where many people still associate modular buildings with temporary structures, modern modular constructions can be built to last just like a traditional build.

PMCs have to meet building regulations that meet or exceed the same building standards required for traditional builds, and many are built using the same materials as regular buildings. While modular buildings undergo tests to ensure quality (and safety), they will still need maintenance just like any other construction to maintain them and extend their life.

With this all taken into account, modular buildings can last for decades and many prefabricated buildings built just after World War Two are still in use today.

What is Volumetric Modular Construction?

Volumetric modular construction is where as much of the construction is completed offsite as possible. This could, for example, mean adding the fittings for a bathroom before the room is brought to site and tied into the rest of the structure.

This type of construction involves the internal finishes being fabricated offsite in factory conditions, cutting down the need for tradespeople being employed on the building site itself. This not only improves health and safety by reducing the number of people needed onsite, but can also reduce the time for the build to be completed.

Benefits of Modular Construction Compared to Traditional Construction

Modular construction offers several advantages over traditional construction techniques. These include:

  • Construction delays due to adverse weather and other onsite issues are not an issue with factory manufacture, eliminating many potential delays to project completion dates
  • Factory conditions allow for a higher quality product with improved operating procedures and monitoring, while employees are able to work in a more comfortable environment. Construction can also more easily be extended 24/7 if required to complete a project
  • Material supplies are easier to control in a factory setting, reducing wastage and thereby cost, as well as lowering the environmental impact of a build. The UK group WRAP, estimates that this can equate to up to a 90% reduction in material use as compared to traditional builds
  • Manufacture of the modules can begin before onsite preparations, such as foundations, are complete, speeding up the whole build process
  • Modular construction allows for different parts of the building to be built at the same time – further reducing the time taken to complete a project
  • Modular construction is highly suited to remote locations where onsite building could prove difficult or expensive. Building away from these locations also means that staff can work in places where medical and sanitary provision is more readily available if required
  • Modular structures can be added to over time or even be treated as a relocatable building which can also be readily refurbished to meet a new need
  • Because modular units need to meet regulations for travel and assembly, the final product can end up being more durable than a traditional build that didn’t have to be assessed part by part
  • Many modular units use Structural Insulated Panels which are light yet durable and provide improved thermal insulation as well as damp and cold resistance when compared to materials like timber. The factory construction also removes the potential for high levels of moisture being trapped inside the construction, improving the quality of the product
  • Modular constructions have been shown to offer time savings of more than 50% when compared to traditional builds, with the inherent cost savings this provides


There are a few challenges associated with modular builds, including:

  • The transportation of finished modular building sections can require a lot of space
  • Manufacturing and transportation restrictions can limit the size of each modular unit, which can impact room sizes


Where modular building used to be associated with temporary structures, improvements in quality, design and unit sizes mean that this type of construction continues to find new applications. From offices to homes and even larger builds like sports halls, the uses of modular construction are constantly growing.

No longer associated with small, low cost structures, the modern wave of modular buildings are proving that they can be used for any number of applications while offering cost and time savings along with comparable levels of quality to traditional builds.

Modular Builds and TWI

TWI’s expertise in joining and construction as well as in associated areas including design and additive manufacture means that we can assist with modular building projects.

We can offer advice on everything from repair and maintenance to fabrication from design, joining, tolerances, rework reduction and developing standard operating procedures. Our expertise in areas including automation through robotic systems can also help streamline working practices.

For more information please email: