16 C O N T E X T 1 3 4 : M A Y 2 0 1 4 •• Because there is no loss of original fabric, the reason for the repair being necessary remains apparent. In repair by replacement •• For a traditional timber joint to work, it must be cut in good undegraded timber, so not only is the degraded timber removed, but sufficient un-degraded timber must also be cut away to create the joint. In a large-section timber such as a tie beam, this can result in the loss of considerable amounts of original material. •• In order to remove the degraded timber, cut the joint and fit the new timber, a significant proportion of the surrounding fabric must be disturbed. In reality, this often means it loses its historic significance. •• The carpentry repair can be dismantled and repeated, but it is not reversible. Once the original timber has been cut away, it is lost forever. •• The reason for the repair being necessary is usually lost along with the original fabric. Costs will vary widely depending on many factors. In general, repair by addition significantly reduces costs as well as loss of historic fabric. When considering the repair of a timber-framed building, or the repair of timbers in any building, the first questions should always be: What is the historic significance of the various elements (all timbers are not equal)? How much can be saved? How can this best be achieved? If a building is standing, that is a good starting point. If it has not fallen over, it does not need a stretcher, just a walking stick. All that should be needed is the (re-) introduction of a sufficient factor of safety.To understand how best this can be achieved, a detailed non-destructive assessment of the condition and the historic significance of each element of the building should be carried out. There is a presumption that, for example, the end of a 300 x 300 beam built into masonry wall with 40 per cent loss of section will automatically require repair. It might, but very simple calculation will often demonstrate that it does not. There is a considerable range of materials and techniques that can be used for the repair of timber. The challenge is to focus on the need to retain historic fabric and the historic significance of the component, without losing sight of the need to retain the architectural significance of the building as a whole. Selection should be pragmatic, not dogmatic: no one method or material should be seen as the preferred choice for all buildings. Indeed, in any one building, even within a single element, it is quite possible that more than one type of repair can and should be used. There are some situations where a carpentry repair will offer the best solution. However, genuinely traditional repairs (which generally fit most closely within the principle of ‘repair by addition’) often result in the retention of more historic fabric. Steel repairs, for example, are often the most conservative in terms of loss and disturbance of fabric and are the most readily calculable, but they can be visually obtrusive when surface-mounted. Equally, there are many examples of sublimely elegant iron and steel repairs, and the relatively small section sizes required will often allow inelegant ones to be concealed. Resin-based repairs often arouse the greatest controversy. They are often seen as a cheap and low-skill solution. In fact they are neither. Quality control on site is difficult to monitor, and faults difficult to correct, but with sufficient skill, resin repairs can be used to produce very successful and conservative repairs, often in timber that would have been lost to a carpentry repair. Epoxy resins and other adhesives are developing rapidly, and while innovative and experimental systems should not be used on historically very important structures, there is a justification and perhaps a need for their use on less important elements, so that their efficacy can be tested in real conditions. The introduction of alternative structural systems or the radical alteration of existing systems can produce some very successful and conservative solutions where more conventional methods of repair would have resulted in significant loss or disturbance to the historic fabric. Often these can be completely reversible. Above all, it is essential that the reasons for the repair being needed in the first place are understood, and the causes removed.There is little point in carrying out a repair if the initial problem has not been addressed. Robert Demaus is director of Demaus Building Diagnostics. The scissor-scarf repair (outlined in red) half way up the corner post of this Grade I market hall is an exemplar of very high quality carpentry. The decay that prompted this repair was confined to the lowest 75mm of the post. It could have been remedied with virtually no loss of original fabric, and at very much lower cost. Unusually, the very large section of post that had to be cut off to effect the repair was retained, and is on display within the building.
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