Last edited 09 Apr 2021

Prefabricated structural panels

[edit] Introduction

Prefabricated structural panels are a form of building product that can be manufactured off-site and assembled on-site, providing an alternative to traditional site-based construction.

They can allow faster construction times, improved quality due to more coordinated supply chain processes, and manufacture in factory environments with controlled conditions. However, detailed design must be provided early in the process as any inaccuracies in or late changes can have a significant impact on cost.

The two main types of structural panels are open and closed:

Open structural panels are a pre-assembled wall framework which are later fitted with other elements (such as insulation, vapour control layers, external cladding, and so on) on site. While this is quick and flexible compared with traditional construction, it still involves a lot of site work.
By contrast, closed structural panels are complete pre-assembled wall panels with the other elements included, such as; pre-fitted windows, doors, ducting for internal services, finishes, and so on. Closed panels tend to be larger and heavier, often necessitating a crane for on-site assembly.

The whole life performance of prefabricated panels is dependent on the long-term risk of failure, the use of suitable materials and the integrity and accuracy of connections between panels, floors and roofs. For more information, see Off-site prefabrication of buildings: A guide to connection choices.

Some of the most common types of prefabricated structural panels include:

These comprise a robust insulated concrete with a brick outer leaf, and can be manufactured with external windows and doors. They are designed to have a service life of more than 60 years.

Structural insulated panels (SIPs) are a form of sandwich panel system that incorporates insulation, predominantly used for residential and light commercial construction. They take the form of an insulating foam core sandwiched between two structural facings. SIPs are manufactured under factory-controlled conditions off-site and can be installed quickly once on site. The benefits of using SIPs are that they are high-strength, high-performance, and can be fabricated to fit nearly any building design.

There are several different types of timber frame system, ranging from open ‘stick-built’ systems to closed panels that are pre-fitted with insulation, wiring, plumbing, and so on. Basic timber frame walls comprise studs fixed in place with sheets of plywood or orientated strand board (OSB). When nailed to the studs, the open panel becomes a rigid box into which insulation can be added on site. A waterproof barrier is wrapped around the frame followed by the external wall cladding. Closed panels are delivered to site with these elements pre-installed, minimising the on-site work required.

These tend to be open panels and overcome the risk of cold bridging by locating insulation on the external side of the frame.

ICF, also known as permanently insulated formwork (PIF), is an insulated in situ concrete system based on hollow lightweight block components. The block components, usually made of expanded polystyrene tied together with plastic or steel ties, lock together removing the need for mortar. This creates a formwork system into which concrete is poured to form the structure. While not strictly being an off-site technique, it can be much quicker to install, and provides better insulation, than other construction methods.