26 CONTEXT 178 : DECEMBER 2023 up-to-date understanding of the timber structure’s form, function, development and setting. A plan also requires an understanding of the current condition and the causes of any deterioration. With timber structures there are many potential areas of concern. The groundsills are often in poor condition due to factors such as minimal footings, poor condition of the dwarf wall, the build-up of the external ground levels and their general high degree of exposure. On external timber-framed walls, cementitious patches applied into splits, open joints or missing wall claddings often raise the moisture content locally. At eaves level the wall plate, bay post and tie beam connection is prone to opening up and decay, as are any rafters and purlins, particularly at their joints and at midspan if water enters due to failing roof coverings. Historically there was less concern about the inclusion of characteristics such as waney edge, sapwood, knots and steep slope of grain, but the effect of long-term loading and carpenters’ joints reducing the effective cross-section can cause fractures or excessive deflections. A consideration that can pay dividends, subject to consent if required, is some opening up of selected areas where further information is desirable. This can help reduce and mitigate some of the inherent risks. This opportunity is often omitted, as project timescales may not tend to factor them in. This investigative phase of the plan can be summarised as ‘what are we looking at and what has happened to it?’ The plan can now allow an informed statement of the significance of the timber structure to be defined. This is an essential staging post, as the conservation proposals will be appraised against their potential impact on this significance. Historic England provides good, clear guidance on this topic. Distinguishing between problems that are defects and those that are failures is the next step towards developing conservation proposals that are proportionate, effective and tailored to the circumstances. Defects can be defined as those issues that are fair wear and tear or inherent with historic timbers and do not materially affect the significance. Failures are those that require some form of action or intervention. This diagnosis of the problems presented is a critical skill that avoids unnecessary work, expense and avoidable harm. Timber structures and their problems can be appraised under a variety of headings, such as their effect on the strength and stiffness, the risk of collapse, the durability, and value or significance. This is essentially a binary exercise, and the reasons to support the judgement as to whether it is a defect or a failure and why should be stated. The plan is now at the stage where all the available evidence has been gathered, interpreted and now synthesised into ‘what do we think about the current situation?’ Proposals for the conservation of the timber structure can now be developed and evaluated. The test will be along the lines of whether the intervention would address the failure and its cause; maintain or if appropriate enhance the significance; and mitigate any harm. In the case of defects such as drying shakes on the internal surfaces of box-hearted beams, due to the well-known differential shrinkage between that across the diameter and that around the circumference, a regime of abstinence is often appropriate. This will be limited to retaining the timber as it is but monitoring it to check if A fractured principal rafter
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