Although the terms "modular" and "prefab" are sometimes used interchangeably, it is useful to distinguish between the two terms.
Any part of a building that is manufactured in a factory before arrival and installation on site is prefabricated - or 'prefab' for short. Modular construction is a specific type of prefabricated building.
A building can consist entirely of prefabricated parts, such as:
- Roof trusses
- Wall panels
- Trusses for the floor
- Pre-cast concrete foundation walls and slabs
- Stairs, lifts, etc.
- Bathroom or kitchen modules
- Structural modules
What is Prefab construction?
Precast parts can be made of various materials, including wood, steel and concrete. Some of these components can be more or less finished before being transported to the construction site and installed. For example, wall panels may be 'open' and arrive on site without insulation, vapour control layers or external cladding. Or they may arrive on site complete with insulation, vapour control layers, windows, doors, electrical wiring, piping and cladding.
What is modular construction?
Modules are a specific type of precast components that enclose space - like an entire room. This is in contrast to 'flat' precast components such as wall panels and roof trusses that do not enclose space. Because they enclose space, modules are also called 3D or volumetric. Whole modules are built in a factory and then delivered to the building site for installation.
According to a 2019 article in Engineering Structures magazine, "Modular buildings made from volumetric modules make up about 42% of the prefabricated building industry in North America."
On site, modules are lifted and stacked by crane and bolted together to create the building. The building is then completed by connecting the MEP systems (mechanical, electrical, plumbing), possibly finishing the corridors between the modules and applying the external cladding. Alternatively, separate corridor modules may also be supplied, or modules where the external cladding has already been applied. The level of finishing of the modules and the amount of work required on site varies.
Combination of modular and conventional construction
A building may consist entirely of modules, or it may include an element of conventional construction. For example, the ground floor of a hotel can be built on site, with a spacious lobby, restaurant and swimming pool. These large spaces may be difficult or impossible to manufacture in a factory and transport to the site by road. Individual guest room modules can be stacked on top of that site-built floor.
The guest room modules can be complete inside - including flooring, furniture, plumbing, even the artwork on the walls! In that case, they just need to be stacked in place, attached to the rest of the building and MEP connections completed.
Another way of combining conventional construction and modular construction is a building that is largely erected on site, but includes modular elements such as bathroom or kitchen modules or lift staircases.
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Permanent or relocatable modular construction
Modules, and the buildings made with them, can be permanent or movable. Moveable buildings are familiar to most people from, for example, temporary school buildings and accommodation on construction sites. Permanent modular building (PMC) is when the building is delivered in modular form and the intention is that the building is not relocatable. Think here of the hotel example given earlier.
Conclusion
All material that is prefabricated in a factory to later act as (semi) complete parts in a building comes under the term Prefab. If these parts are volumetric like a complete bathroom unit, for example, then we speak of modular construction.
At Ripstaal Group, we use both methods. The façade elements used to renovate existing facades or to raise facades in new buildings fall under the heading of Prefab. We also make complete chalets that only need to be installed on site and connected to the facilities. This chalets fall under the heading of Modular Construction. At Ripstaal Group, all precast parts are made on the basis of Steel framing.
Are you interested in prefab or modular construction or want to know which opportunities Ripstaal offers? Then take a look at our Stone framing page or contact us via the form below or via the contact page.
