What is modular construction?

Modular construction is a building method in which a building is assembled from prefabricated three-dimensional units (modules) that are largely made in a factory and then placed, joined and often stacked on site. It is also called volumetric construction and is a form of offsite or industrialised construction. In Dutch it is called ‘unitbouw’ or ‘modulair bouwen’.

How it works

Each module is a self-supporting box with floor, walls and ceiling, often the size of a shipping container or larger. Depending on the system, services, bathrooms and finishes are fitted in the factory. On site, a crane lifts the modules onto the foundation, where they are connected and hooked up. Walls can be left out where modules meet to create larger rooms. Assembly is mostly dry, so it is fast and often demountable. Timber, steel and concrete modules are all common.

Temporary, semi-permanent or permanent

• Temporary: site cabins, temporary classrooms, event welfare units.
• Semi-permanent: student housing and the Dutch ‘flexwoning’ (flex home), placed on a site for a limited number of years to ease housing shortages and then relocated.
• Permanent: houses, apartment blocks, care homes, hotels and offices.

Application

Modular building pays off when speed matters, when many identical units are needed, or when the building may move later. Because most work happens indoors, there is less disruption on site and less dependence on the weather.

Tips and points of attention

• Permits and regulations: a modular building is still a building and must meet the local building rules. In the Netherlands it needs an ‘omgevingsvergunning’ and must meet the Bbl (Besluit bouwwerken leefomgeving), which replaced the Bouwbesluit in 2024. Elsewhere, check with your local authority.
• Permanent living: check that the units are designed for permanent occupation, not only for temporary use.
• Sound insulation: double walls and floors between modules help, but the junctions decide the result. Ask for test results from earlier projects.
• Transport: oversized modules need abnormal load transport and good crane access to the site.
• Freeze the design early: changes after production starts are costly.

Related terms

• Industrial construction
• System building
• Flex home
• Timber frame construction
• Building permit

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