The use of timber as a construction material throughout the ages, and what technological advancements have brought it back to the forefront of the construction industry?
Edwin Westwell - N0521458
Box frame construction
The transition from earth foot timber structures to sill mounted structures meant that a permanent framed building of box frame construction occurred in Britain between the years 1150 and 1200. The name is self-explanatory, consisting of a box-like framework with the roof load distributed along the supporting walls. This is in contrast from cruck construction where the walls are non-load bearing and rely directly on the crucks (Angus, 2007).
Box framed buildings are based on the use of a pair of posts held together at the top by tie beams, connected laterally at the bottom by a sill beam and at the top by wall plates. These wall plates support the feet of the common rafters that make up the framework of the roof. Further lateral support is generally provided by a girth, a horizontal member placed about half way between the wall plate and the sill beam. These basic components, together with various angle braces, form the basic box framework (fig 5) (Brown, R. J, 1986, p42).
Fig 5, Box frame construction. (Unknown)
The secondary vertical timbers, studs, frame between the sill beam, girth and wall plate, these only serve to reduce the overall size of the panels. The sill beams sit on a stone plinth that forms a solid, flat foundation and raises the timbers from the earth, therefore reducing the risk of damp and rot. The common rafters that sit on the wall plate are connected laterally by purlins and at the peak by a ridge beam. These early box frame constructions would have had a straw thatched roof with wattle and daub to infill the timber frames (Brown, R. J, 1986, p42).
The above describes the basics of a medieval box frame construction in England. However, there is a great variety of forms, not only in wall framing, but also in decorative styles. Many features of these constructions were regional and often changed over time, with one often intertwining with others to form hybrid patterns.
The characteristic feature of medieval timber wall framing is the use of large open rectangular panels consisting of vertical posts connected laterally by a wall plate at the top, sill beam at the bottom and a girth in the centre. The mortice and tenon joint and halving joint (fig 6) were the joints of choice used by a carpenter to connect these components (Angus, 2007).
Fig 6, Halving joint. (Westwell, E. 2017).
A variety of bracing methods for these panels were used throughout the years: herringbone, scalloped, circular, cross-bracing, arch-brace, tension-brace and arch-bracing cusped were the most common found. Although initially used for structural purposes, these braces also became decorative, noticeably through the Georgian period and even more so in the Victorian period (Brown, R. J, 1986, p42-43).
Another predominant early feature of box framed construction was the use of dragon ties that connected two adjoining walls to triangulate the framing on the horizontal frame (fig 7). This bracing became a fundamental part of timber framed construction, adding necessary stability to larger structures (Brown, R. J, 1986, p45).
Fig 7, Dragon tie connecting adjoining walls. (Unknown)