The pros and cons of different offsite systems – and the applicability of the systems in the bespoke residential sector.

Although prefabrication has been a feature of the UK building industry for many years, there is still a perception that the use of off-site manufacture results in a generic approach to design.

This view is gradually changing as architects are starting to explore the opportunities that Modern Methods of Construction can provide, particularly within the bespoke residential sector. Increased exposure of MMC through the mainstream media is helping to reposition new building technologies within the market, with television programmes such as Channel 4’s Grand Designs recently covering a number of homes built using off-site systems. As a result, consumers are beginning to understand the advantages that this approach can offer.

The key to unlocking the benefits of MMC is understanding the strengths and limitations of the various systems available, and the applicability of each to particular design requirements. It is only through an intimate understanding of each product that it becomes possible to select the most appropriate type for the application. This is particularly important when it comes to designing bespoke homes.

Assessments of the different systems for particular construction projects are usually made on the typical basis of Cost, Quality and Time and most manufacturers have marketed their products by quoting fast construction times, excellent build quality, good thermal performance, value for money and so on. and whilst valid, these attributes should in fact be secondary to the important considerations for a new home.

The general assumption is often that most systems are similar in their application, and as a result design limitations are often overlooked. On a number of occasions we have been approached by clients wishing to build using a particular system which isn’t always appropriate for their specific requirements. It is important to stress that when designing a bespoke home there are more fundamental things to consider, such as ensuring the proposals suit the client and their way of living. It should also be location-specific in order to unlock the full potential of the site, to achieve planning permission and take advantage of the local environmental conditions. Once these parameters have been defined it is only then that we would investigate which system is the most appropriate.

There are generally three categories of off-site system suitable for the bespoke residential sector.

The first is the heavily-branded ‘whole house’ systems which tend to deliver only limited flexibility in their design, whilst achieving very high build quality. In these cases, almost all of the components are manufactured remotely and brought to site for assembly. Design options are usually limited, and bespoke details are usually impossible to achieve. Opportunities for responding to the site are limited as a result. There is a second category of ‘whole house’ systems which offer more flexibility by using a kit of standard details to achieve a bespoke home, either in conjunction with an architect, or using an ‘off-the-shelf’ design. Minor alterations to the standard set of details can usually be achieved, but significant departures can be harder to accommodate.

The systems offering the most design flexibility are those which provide prefabricated structural components, but which are finished on site. This third category includes timber frame houses, SIP systems and others. Here, the primary structure is brought to site to be assembled within a short space of time, and then completed on site with the required internal and external finishes. Whilst this type of off-site construction offers the greatest levels of flexibility and adaptability, quality control and achieving a tight programme are generally more difficult to achieve.

Generally speaking, those systems which offer a high degree of off-site prefabrication tend to deliver less flexibility than systems which combine a level prefabrication with on-site finishing. Much of this has to do with the control that manufacturers require over the various building components. For instance, some offer a choice of window systems whilst others are limited to a standard range – and not always the ones that the architect would ordinarily select.

Another determining factor is often the proximity of the site to the originating factory. Systems which involve a high level of off-site assembly tend to reduce in their capability to adopt bespoke detailing the further they are from the point of manufacture. We have investigated a number of systems originating in mainland Europe which offer a great deal of choice for sites on the continent, but because of logistical issues are able to accommodate less flexibility in the UK where bespoke components cannot easily be flat-packed for transport. With all this in mind, it is impossible to determine which system is the best, but only which is the most appropriate on a case-by-case basis. All offer high levels of environmental performance, enhanced build quality, accelerated construction time and better sustainability credentials over traditional construction methods. The choice will largely depend upon the needs of the brief, and it is this factor which should always lead the choice of system.

Unfortunately there are many bad examples of where MMC have been used to create bespoke houses. Such examples do not take advantage of the potential of MMC and have been built in such a generic style and with so little consideration for design that they would not be out of place on a volume housing estate. The other extreme is that the product chosen is so prescribed that the resulting house does not respond to the needs of the inhabitants or the site, but suits the system perfectly.

We cannot blame the manufacturers for these results and we should be thankful that there are so many different systems to choose from. It is more a question of the product being considered in the right way: people are often not aware of the choice available to them or how far a particular system could be pushed to suit their needs. The ’system’ is not ‘the house’ but one of many potential tools that can be employed to deliver a beautiful, contextual and personal home.