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Pre-fabricated timber framing

Due to the risk of fire, horrifically demonstrated in the Great Fire of London in 1666 (Johnson, B, 2012), and the rising cost of timber in the late 17th and early 18th century, the construction industry began to change. Gradually leaving behind timber frame construction, making way for brick construction. Although timber framing still occurred throughout Britain, brick construction quickly became the most popular method of construction.

 
The years that followed World War II saw a war-ravaged country desperately trying to rebuild itself and create affordable homes quickly, with very few skilled tradesmen to erect them. This sparked experimental ways of producing prefabricated buildings. Famously, these years spawned the confrontational architectural movement that is brutalism, using prefabricated and in situ concrete to form houses and gargantuan structures replacing the buildings of old (Johnson, B, 2012). It was during this period that timber framing also found its feet again by becoming a more refined version of its medieval self. 


Modern British timber framed construction has its origins in North America and Scandinavia, where timber framing continued to be the primary method used whilst Britain moved towards brick construction. Timber framing was experimented with post-war and became widely adopted in Britain in the late 1950s. In 1957, the Canada house, an early example of pre-fabricated timber framed housing was promoted at the Ideal Home Exhibition as a modern, cost effective, energy efficient alternative to the brick and block houses that had been constructed for decades pre-war. The huge demand for housing throughout the country and the lack of skilled workmen made timber framing a popular form of construction for both public and private sector housing; the main attraction being an overall saving of up to thirty percent in comparison to a brick and block building of the same size. Due to timber being a lighter construction material, this allowed for up to a thirty percent saving on foundations alone, which also lent itself well to construction in areas where the ground was of poor quality (Wanderer, O, 2014).


Prefabrication of the building offsite and quick erection when delivered to site saved on building time and labour costs. This style of construction is not weather dependant like brick and block construction, again saving time and money throughout the process. In the 1960s and 1970s, the boom in popularity brought about hundreds of companies developing their own timber frame systems throughout Britain. By the beginning of the 1980s, twenty percent of new houses being built in Britain were timber framed.  A burst of bad publicity in the mid-1980s with regards to the life span of timber framed houses damaged their reputation, however surveys concluded that timber frame houses are no less reliable than traditional brick and block cavity wall constructions in terms of defects (Wanderer, O, 2014).


Beginning life in a factory, the load bearing wall panels (fig 8) that form a building are tailor-made to the building’s individual requirements. These wall panels are made at storey height and between three and three and a half metres in length, comprising of vertical studs fixed laterally top and bottom to horizontal timbers. These timbers are generally softwoods from Scandinavia, as the cold climate and slow growing seasons create strong, dense timbers suitable for construction.  The outer face of the walls is then covered with sheet timber such as ply wood, to add rigidity and strength. Where windows are required in the stud walls, cripple studs are added to support the timber lintels that create the openings. A vapour permeable, waterproof fabric is stapled to the outer face of the stud wall which shields the timber from damp during construction. As the fabric is vapour permeable, it allows any trapped water to escape to help prevent condensation (Wanderer, O, 2014). 

Fig 8, Pre-fabricated stud wall being lifted in to position. (Unknown)

Once onsite, horizontal timbers, known as sole plates, are set out and fixed to the foundations to create the floor plan of the building. Between the sole plate and the foundation, a damp-proof course is added to protect the timbers. The ground floor stud walls are then screwed to the sole plate, forming the ground floor envelope of the building. Head binders are screwed to the top of the wall panels to align them and a header joist then screwed on top of that, leaving a ledge on the internal side of the head binder. Floor joists span the tops of the stud walls fixed onto the ledge of the head binders and butting up to the header joists. Stud walls fix to the top of the header joists and floor joists, forming the envelope of the second floor. Again, like the first floor, a head binder is screwed to the top of the stud walls aiding in alignment and roof trusses span the tops of the second floor walls. Purlins and a ridge beam support the roof trusses laterally. This process forms the skeleton of a timber framed building and is carried out in approximately one week for an average sized house (Wanderer, O, 2014).

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