22 It is interesting to note that the appellants introduced three thatchers and an architectural historian as expert witnesses. This is a greater number of experts in the same discipline than I have ever seen at an inquiry. The inspector commented, however, that they disagreed amongst themselves about the question of block cut and flush ridges. One said in his book that wrapover ridges are usual with straw roofs but at the inquiry said that this was far from the case. This inspector also accepted that long straw was the typical thatching material of Northamptonshire. He considered that the second main issue was whether a block cut ridge was historically alien to a long straw roof. Despite the fact that the thatchers disagreed amongst themselves, the inspector considered that their evidence complied with SPAB guidance in The Care and Repair of Thatched Roofs that reliance should be placed upon advice from thatchers of good reputation. The inspector was convinced that, while the block cut ridge had a different appearance to the wrapover roof as it existed when the building was listed, it was appropriate to and historically compatible with a long straw thatched roof. He therefore granted consent. I conducted a random sample of local authorities in the major thatched areas of the country while I was preparing this article. The most interesting point that I discovered was that there is no unity of view as to whether the replacement of one type of thatch with another or a change in the ridge detail require listed building consent. The conclusion from the three Northamptonshire appeals is that quite clearly both rethatching and re-ridging do in normal circumstances affect the character of the building and therefore require listed building consent. As far as Northamptonshire is concerned the decisions also establish long straw as the traditional thatching material. Perhaps the reasons why the inspector supported the block cut ridge as opposed to the historic wrapover ridge at 40 Main street, Sudborough was, in the days of plan-led planning, the absence of a formally approved policy on the subject in the relevant local plan and also the value placed upon the weight of professional evidence used by the appellants. It is clear that if a local authority wishes to be successful in opposing a particular type of ridge detail it will have to employ thatchers of a good reputation. The three who disagreed between themselves at Sudborough obviously fit the bill but what about Margaret, Dennis and Mark? The first authority to employ that trio will be sure to win the appeal. David M Morton is the principal of Conservation Consultancy and is also a consultant with Hammond SuddardsResearch. Brian l\1orton discusses the difference in approach to engineering conservation needed for new and historic buildings. 'SUPPORTING COLUMNS' This article, rather than following the pattern of our previous articles for Context, is about the general subject of engineering conservation, suggesting the difference in philosophy necessary between work in new buildings and on historic buildings. A recent consultancy engagement in Singapore suggested to us that there is very little acceptance of the principle that, if a building has stood up for several hundred years without problems (and is helped along a little), it will probably stand up for several more centuries. The ability for lateral thinking is the essential ingredient of engineering works to historic buildings. In the Singapore situation, I found that there was very little knowledge of the behaviour of brick structures, particularly the performance of the brick walls used in the many thousands of shop-houses. The Singapore shop-houses (in structural terms) are not a lot different from similar buildings throughout the world, where trading takes place on the ground floor and the upper floors are used for living accommodation. The structures can be classified as falling within four age or period ranges beginning with 'early' types (circa 1840) of two-storey construction, through the 'transitional', followed by the 'art deco style' and ending with the more recent buildings and 'modern' forms. All of the structures follow the same brick and timber design except some of the later ones which are of reinforced concrete construction. Without exception they all have brick party walls which seem to be a major structural worry for engineers there. It was considered before our period of consultancy that these walls, although structurally and generally sound, could not be relied upon to carry additional live loads and, generally, no attempt was made to calculate such loads. Surprise was expressed when I indicated that I had never actually seen the failure of a brick structure caused by crushing. Walls invariably fail because of lack of lateral restraint. Many collapses had occurred to these walls, frightening the engineers and causing them to press their clients to install internal concrete frames to support the floors. I found out after detailed investigations that their conservation philosophy seemed to be to take out all the timber floors and remove the roof and then use raking shores to support the walls. Eventually those raking shores had to be taken down while the new floors were inserted, and this is when the collapse occurred. My basic philosophy put across to them was that the existing roofs and floors should be retained and elements of the structure replaced where necessary, in a piecemeal manner, allowing the floors and roofs to maintain the structural stability of the party walls. The idea of repairing the buildings, working from the top down, seemed to be a great surprise to them. I explained that if you are going to replace a shop front beam, it would be a good idea to repair the brickwork first. This was something that had not been thought about. Considering this experience in the context of UK engineering conservation and looking at the methodology used in our practice, I realised that what is common sense and, indeed, common practice to us is foreign to the general teaching of engineering related to modern structures. The Charter of The Institution of Civil Engineers requires that we should be "capable of harnessing the _great sources of power in nature for the use and convenience of man". I cannot see that we, as engineers, can have the right to look at structures that have been engineered using this philosophy, and simply abandon them because they do not hold up to a set of modern rules. Considering the various forms of structural schemes currently in our office, we can generally look at these individually and use a conservation approach. For example, with a timber frame building, the sizes of timber are generally so massive that calculations are not necessary to justify the existing construction, and traditional repairs can be used without any worry. With brick structures, depending on the situation, experience will guide us but invariably we carry out calculations as to the loads that we are dealing with and the possible strength of the brickwork related to the storey heights and provision of lateral restraint to the wall or brick structure. As previously indicated that I have never seen a brick 'buildings CONTEXT 36
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