Off-site manufacture could become the most influential technique of the 21st century. Barbour Index and Scott Brownrigg look at how OSM can already add value

Political pressure and industry demand are putting off-site manufacture under the microscope.

Given these pressures it is inevitable the OSM sector will expand in the next few years. If developed logically, this expansion could lead to high-quality buildings, using assembly techniques and an approach to quality control taken from car-making. Such an assembly process would tackle some enduring problems of the construction industry: it uses relatively unskilled labour compared with the traditional trades, health and safety is easier to control in a factory than on a site and the production process is easier to manage.

From cars to homes

The controlled environment of the production line means that new material and assembly techniques could be used. We can look forward to better insulation and more sophisticated use of coatings to enhance thermal and acoustic performance. Interiors could have advanced and concealed plumbing and wiring, and finishes without visible fixings and fudged joints are also possible.

Flexible manufacturing techniques could also deliver far more variety than is possible on site. The prospect of ordering a home with the same degree of specification choice as a car is entirely possible. The ability to add on modules as a family needs change is also possible. And this could all be realised for less cost than a home build using traditional techniques.

The industry today

The current off-site industry will not deliver this. The OSM sector in the UK is a mix of cottage industry and disjointed, parochial manufacturers. This fragmented nature means that the industry is failing to embrace innovation – a state similar to that of the UK car industry before the Japanese came along with their manufacturing expertise. The current offerings owe more to 1950s prefab principles than sophisticated 21st century factories. Unfortunately there are too many closed minds and vested interests for the industry to develop, so the potential of OSM will probably be realised by manufacturers outside the present construction industry.

There is one exception to this situation – the potential of OSM is being realised in small components for walls, roofs, some internal finishes and bathroom pods. For several years this area has been well served, and products have high specifications, accurate delivery and superior build quality. Until the new wave of OSM products arrives, the specifier should take great care and check at first hand any products or buildings being considered.

1. Check the manufacturers out

There are several manufacturers offering bathroom pods and small components in the UK and abroad that have a well-established track record and can demonstrate a significant level of expertise. The specifier should check previous projects and the history of the manufacturers in detail prior to specifying. A tour around any of the established players in this field will clearly demonstrate the accuracy and finish achievable. Remember this is a product and should be treated as such. If this route is chosen the specifier should ensure that the units are clearly defined and specified as early as possible. Although the specifier should make at least one factory visit prior to placing an order it is better to additionally visit during manufacture, and once it is completed. This ensures minimal errors and avoids faulty units being shipped to site.

2. Consider European manufacturers

In Europe the OSM situation is a little better and the housing market in Germany in particular supports a host of high-quality operations, delivering well-designed and well-finished homes. If high-quality units for upmarket housing are required, consider sourcing from Europe. This solution is not cheap, however – this type of quality is expensive. However, well-resolved design and fast build times come as standard.

3. Framing

Two carcassing systems are currently available: concrete or steel frame with timber infill. Concrete provides a solid and stable background and is able to provide good acoustic and structural separation.

However concrete is also heavy and bulky, making it difficult to manoeuvre into place. Steel frames are lighter and can take up less room, but they can also be subject to buckling during installation and may suffer from corrosion if moisture from services is present and weather protection is inadequate.

4. Detailing

There is a risk of deterioration of the structure if the unit is not carefully detailed, particularly around services. Any gaps can result in slow, long-term exposure to moisture. Ensure that the services connections, in particular, are co-ordinated, with all disciplines taking part, and the exact connections sequence and access for maintenance is well detailed.

5. Installation

Installation of the units is particularly critical and must be checked thoroughly as the installation sequence is fundamental to success. Simple computer models may prove useful for checking that the installation process has been properly thought through in advance. Also, carefully consider how the pods are to fit in to the building without the carcassing being obvious. This is partially crucial for floor-level pods.

Remember: OSM is a great method to use in order to achieve quality and reduce site operations, but handle with care and keep to simple solutions. Examine all the details closely in the office and the factory. OSM is not a panacea but can help create a better building.

Barbour Index

Subject guides similar to this are available from Barbour Index as part of its Construction Expert and Specification Expert services. For further information, contact Barbour Index on 01344-899280 or visit