Demand for Offsite Construction Continues to Rise

The practice of offsite manufacturing has been around for hundreds of years; the first example being recorded in 1895 by Sears Roebuck and Company in the US, who began selling new home-building kits. Over the past few years, offsite manufacturing has become a preferred method of construction for many specifiers and contractors.


Dan Gleeson

is THE Head of Commercial Sales for Reynaers Aluminium UK

Prior to 2022, offsite construction accounted for around 2% of the total construction market. While latest figures estimate this is set to grow by around 6% by 2029. Here, Dan Gleeson, Head of Commercial Sales for Reynaers Aluminium UK, discusses the advantages of offsite manufacturing and benefits specifically for unitised, panelised and modular construction.

Offsite manufacturing is a relatively modern approach, which involves sections of an external wall being constructed off site; this can be panelised, unitised or full sections of the building. Panelised facade systems are like unitised ones, but the prefabricated modules are generally much larger to incorporate different materials and components (such as windows). This process significantly expedites the construction and installation processes, making it more efficient, saving both time and money, requires less skilled labour on site and generates fewer carbon emissions.

With ambitious net-zero targets on the horizon, using modern methods of construction (MMC), such as offsite manufacturing, is an effective way to decarbonise some of the production processes. For example, delivering building elements in a controlled environment enables contractors to ‘get it right the first time’. This means using fewer materials, emitting less carbon and driving efficiencies.

More efficient – less labour

Much of the construction that would traditionally take place on site, occurs in the factory. The prefabrication of components in a controlled environment increases the quality of the product and reduces some of the workmanship issues on site. The speed of installation on site is also much quicker with both panelised, unitised and modular or volumetric construction, which saves both time and money. While unitised facades are tested to withstand the most onerous conditions, panelised and modular or volumetric may require some onsite water testing, especially if some of the joints are sealed prior to transit.

The unitised approach to glazing and facades

Implementing a unitised approach to glazing and facades can yield significant benefits. Unitised systems consist of prefabricated units that are fully glazed and sealed off site. The complete units are then moved to site for swift and easy installation onto the steel or concrete frames with integrated location and carrying devices locking the panels in the correct relationship to one another.

Offsite manufacturing offers greater control over the process and ensures the quality and consistency of all systems and components. This is particularly crucial for the unitised facade elements, which must be fully compliant with the latest Building Regulations and be robust enough to withstand the UK weather. Manufacturing off site means each unit can be monitored and checked for compliance and performance before leaving the factory. This not only reduces the risk of defects but also prevents issues on site, which can be more difficult, time consuming and costly to rectify. Prefabrication in a factory environment also minimises the risk of damage and so reduces the chance of waste.


With panelised construction, we typically see windows glazed into openings formed from precast concrete panels. The windows are installed off site and glazed; in some instances, they are then fully sealed with EPDM perimeter seals and internal air seals. The panelised component is then sent to site and craned onto the building. Typically, there will be a water test regime in place, either spray bar testing of opening elements or hose testing of fixed joints while on site.

Modular or volumetric

Modular or volumetric construction is slightly different in that the modules provide the internal walls of the building as well as either a primary or secondary structure. When the structure gets to a certain height, it needs to be connected back to the building’s core to ensure that excessive building movement does not occur. The steel modules then form external walls with steel frame system infill or, in instances, containers have been used. The external wall build up is then mounted to the relative face of the module, with more conventional external wall build ups, such as rainscreen, then stick curtain wall, unitised curtain wall, windows or doors can be installed in the apertures created. As with panelised construction, water testing will likely be required to ensure that all seals are in place and correctly connected.

Less time – fewer delays

Offsite fabrication also significantly reduces the amount of time required on site. The delivery of the facade units to site can be scheduled for exactly when they are needed and installed quickly, preventing clashes with other contractors and trades and minimising delays to the overall build. The progress of a project is also less reliant on the weather conditions, something that is becoming more important as the UK’s weather becomes more extreme and less predictable.

Offsite construction also has the potential to improve the way we design and construct buildings, driving improvements in quality, safety and cost. However, it does require closer collaboration between members of the supply chain throughout the project, so early engagement is required. The companies required to deliver large-scale unitised projects must have the correct technical and commercial infrastructure to be considered for these projects, and while time is saved on site, the design period is protracted and adequate time in the programme needs to be allowed for. It’s vital, therefore, that the industry continues to embrace a more integrated way of working across the value chain to ensure it continues to take advantage of the benefits offsite construction methods provide.

Reynaers UK is a leading expert in the design and installation of unitised, panelised and modular window systems and facades for the commercial sector. To find out more about its expertise and projects, visit the below website.

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