The traditional approach to building, which the simplified diagram below attempts to explain, shows a distinct separation of roles between the (coordinated) design team and the building contractor's team. The design team need to ensure that the contract information provided to the contractor is accurate, buildable and coordinated. Once on site, the main contractor is responsible for the delivery of the built project and often has the lion's share of control over the works, within the parameters of the contract.
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| Simple diagram which aims to illustrate the relation ship between designers and contractors on a traditional build. For comparison with those below. |
With all the technologies available to us on the twenty-first century, it is surprising that building is still such a messy process, relying on wet trades and estimated quantities of base materials brought to site which, by comparison to other manufacturing methods, can consume a lot of materials and produce a lot of waste.
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| Even with the huge demand for housing, most of it is produced using site based labour and traditional trades. |
The UK saw it's chance to adopt production line technologies for the first time, after the Second World War, in the post-war rebuilding programme. Using the aircraft industry to support the building industry, surplus war planes were recycled for their aluminium and converted in to bungalows on a mass-produced scale. Working under factory conditions brought designers and fabricators to a closer working relationship. The factory environment also allowed greater control, use and re-use of materials, thereby limiting waste. The product was typically four building sections which could be fitted together by a site team, on a prepared site, in one day to make a house.
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| The production line promised to bring design and fabrication roles closer together. The factory environment allowed greater control and accuracy over the product. Material quantities could be more easily controlled, with the ability to reuse surplus materials and recycle waste. |
The most successful product (by quantity) was bungalow B2 by the Aircraft Industries Research Organisation for Housing (AIROH). Over 54,000 units were produced by four aircraft manufacturers in the UK, including the Bristol Aeroplane Company in Weston-super-Mare.
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| The first production line in the UK to produce buildings! |
Logistical restraints play a vital part of prefabricated construction. The bungalows were transported to site, by road in four sections as shown below for an exhibition at the Tate in 1945.
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| Four sections of the bungalow B2 arrive at the Tate in Pimlico, London. |
Specific on-site plant for lifting and manoeuvring the prefabricated units was also essential, as was a site team experienced in handling and assembling the prefabricated units.
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| The pre-fabricated sections are positioned on a prepared base. |
The sections were pushed in to place, and junctions welded up to make a watertight enclosure. The services were also connected to the main infrastructure through the base.
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| Making the connections and completing the assembly. |
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| With aluminium in abundance, and many workers experiences in fabricating this material in the 1940's even the kitchen, including the doors, was made with aluminium. |
There were disadvantages. This approach lends itself to a standardised single product solution. Variation in the product is difficult to achieve and not cost effective. That's why cars are identified as particular models and makes, with variations generally restricted to colour, optional extras or whatever you might add in the way of stickers or furry dice etc. Another disadvantage is that factory based production systems often rely on a set range of components, prescribed by what is on offer within the factory. The material palate and selection of details can be limited. Also, one key disadvantage to this trial was that although the houses were produced quickly, they cost significantly more than their traditionally built alternative.
With these bungalows, there is also the thought that the aircraft industry did not capture the imagination of the public (or design professionals) with these aluminium homes in the same way as we idolised aircraft manufacture, the marvels of flight and how it was achieved with structures like the monocoque fuselage. The bungalows, although very adventurous in many ways, didn't seem to have the same progressive aesthetic. Perhaps too many building details were lifted from existing war time structures familiar to the manufacturers, which consisted of temporary buildings and military camps. With the details followed some of the aesthetics. It would be an interesting investigation to look in to how much the Architectural profession and building industry was involved in these production line experiments because following the Second World War, the RIBA was active in trying to return the building industry to more traditional materials and production methods. I suspect they were driven mainly by the aircraft industry.
These bungalows were also a product of central government control. At the time, the Ministry of Works wanted to see what could be achieved with factory production, new materials including metals and how they could be combined as composites. There was a surplus of people who had been working for the war effort, with factory skills needing employment after the war. There was also an active steer away from traditional site labour and traditional building materials such as brick and timber, which were in short supply. This is why most of the photos of post war bungalows show them sitting behind wire fences with concrete posts above concrete paving slabs. The environments look a bit austere by today's more demanding standards, but they offered a marked improvement in their day.
Today production line buildings largely restricted to producing Portakabins which we identify as a standard temporary building type with limited aesthetics, or modular buildings often for service and utility use.
The traditional site-based approach to building does have a key advantage over the production line, that each building product can be made different and individual, and it is this versatility and flexibility which the building industry works well with and relies on for the variation we have in the built environment. There are several advantages of the production line approach and prefabrication which we can draw on to make the site based approach more efficient, quicker and potentially more economical.
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| Using prefabricated specialist products with closer integration and coordination during design offers millimetre accurate components which can potentially be transported to site from different locations, with confidence that they will fit and perform as required. It also potentially means a closer, more integrated working relationship between design professionals. |
More and more, prefabricated components have played an increasing role in the building industry. Even on the standard housing build shown above, items like window units and roof trusses will be prefabricated. The more which can be prefabricated, the less chance there is of un-necessary site waste, and the quicker the site programme. There is the potential to involve less wet trades on site, and for buildings to weigh less, using less material resources.
This process relies on the close involvement of specialist fabricators to work at its best. BIM and 3D CAD has given us the opportunity to share design information with specialist fabricators with the confidence that items produces will (or should) fit on site. It gives a huge range of choice for material and detail selection because specialists can be chosen to suit the project, supporting the building industry's requirement to produce individual buildings or sets of buildings with variations.
The Richard Rogers Homeshell project is a great example of this approach. It uses a set range of components which can have variations as required for each house type.
The system is very simple, which should help to make it economical as a competitor in the housing market. The key ingredient is the Insulshell panel. This provides the airtight external insulated envelope, primary structure and lateral stability to the house, with timber framed prefabricated panels. The design of the system allows complexed geometries to be managed.
The fabrication is kept simple, as is the and jointing and weather sealing. The external walls are clad with a rainscreen and the inside lined out with a plasterboard finish.
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| Looking up to the underside of the roof and it becomes apparent that there is no separate structure. The timber panels do all the work. They are the primary structure, lateral stability, thermal resistance, air tightness and set out the geometry of the building. |
The inside reveals that there is no additional structure. The Insulpanels are doing all the work with a combination of timber assemblies. This greatly assists the speed of the build and should help to reduce costs, but it also means that during design the Architect, Structural Engineer and Specialist Fabricator need to work closely together on this one product. This is something that has been noted before in a previous post. It means a departure from the traditional way of working where each consultant works on their separate area of expertise and the Architect coordinates to check that everything will fit, with the proposals then going out to the market for pricing. Here structure, aesthetics, and environmental requirements (insulation and air tightness etc.) are all rolled in to one product. Speaking to Don Blacklock who heads up the Insulpanel division of SIG, he stressed the importance of involving specialist fabricators in to the design discussions as early as possible, to make the best use of the potential efficiencies and economies available (which in my experience is before the Structural Engineer can say 'cross bracing').
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| Internal walls are structural timber cassettes, performing several design roles. |
Key to all prefabrication projects, as noted above with the aluminium bungalows, are:
- Logistical restrictions and the size of components which can be carried to site,
- The correct lifting plant and
- Use of trained installation teams on site.
Perhaps the biggest hurdles to this type of development taking off are:
- Economics. The system (product and process) must have proven cost advantages over traditionally built houses. Products like Insulpanel must be cost effective compared to a cavity brick wall, which is one reason it looks so simple.
- A shift in the structure of design teams: More integration over component design with the involvement of specialist suppliers as part of this process.
- A shift in the way the building industry works: Managing specialist fabricators in relation to supply to site in relation to programme. Addressing logistical restrictions and specialist lifting plant requirements to replace lorry loads of materials and scaffolding.
- Contractual responsibilities: Including clarification of design responsibilities which result from more integrated working relationships. Also there are issues over who would be responsible for sub-contractor appointments, if they are tied in to the design leaving the main contractor no choice but to adopt them.
- Aesthetics: An alternative solution to traditional building needs to be accepted by the public as a clear preference to traditionally built homes, or the victorian terrace etc. The solution needs to be marketed so that it is not seen as an experiment, temporary or something different or quirky.
Some lines of development to be played out?
References:
- Prefabs (1995) by Brenda Vale
- Palaces for the People (2003) by Greg Stephenson
- The Royal Academy Richard Rogers Exhibition, Inside Out
- Housing by People (1976) by John F Turner
