CONTEXT 185 : SEPTEMBER 2025 19 ROOFING Not surprisingly, both documents promote the need to record roofs, particularly ones that have not been substantially altered for a century or more and may contain important examples of rare vernacular techniques. The article on Melin Daron illustrates how important this is. Historic roof detailing is one of the most neglected areas of research, yet it is of singular importance in terms of the attractive appearance of a roof and understanding much of its history. These local traditional roofs are also a quintessential element in defining the character and unique identity of an area, village or individual building. A careful study of the detailing will also show how the roof has managed to perform so well without the ubiquitous use of underlays, and features such as lead valleys and flashings. Problematic issues Most of the advice in the new documents is intended to ensure maximum retention of original or authentic materials and details. Despite the advice differing from much modern practice, from a conservation perspective it is essentially non-controversial. Some issues, though, are more difficult. Obtaining slates (especially stone slates) from authentic sources for repair often poses a problem, as many historic quarries have ceased production. Advice has consistently encouraged using new materials, rather than secondhand, to help sustain a small industry and ensure continuing supplies of material and the skills to make them. If it is not possible to source authentic new materials, a decision is needed as to whether to use matching secondhand, find new material that is a good geological match (possibly from abroad), or use a totally different slate or stone slate, such as limestone instead of sandstone. Using another material altogether – such as tile – is another option to consider. The answer will be case-specific, but the TAN will provide advice on assessing the options in the context of sustaining building significance, as well as the wider benefits of supporting indigenous slate and stone slate production. Another problematic issue is the question of felts, underlays and permeable membranes. These have mainly been developed in the latter part of the 20th century and, as the National Federation of Roofing Contractors (NFRC) Bulletin (TB06) states: ‘permanent underlays are universally accepted practice in the UK’. Originally used to reduce draughts and powdery snow ingress, as well as wind pressure, modern permeable membranes in particular are now advocated as a way of dealing with moisture loads in more thermally efficient buildings. Perhaps their main advantage is that their installation keeps a building dry during roofing works, but they can mask poor workmanship by hiding leaks. The NFRC Technical Bulletin on Pitched Roof Underlays states that vapour-permeable underlays can be used in ventilated and nonventilated cold and warm pitched roofs, subject to the ceiling and associated wall junctions being sealed against internal moisture transfer, as set out in BS5534 and BS5250 (Management of moisture in buildings). The problem is that it is extremely difficult to retrofit effective seals in old buildings. It is perhaps better to rely on the capacity of roof timbers, boarding, laths and lime-mortar torching to buffer moisture in the roof, as was traditionally the case, even in ones that were not ventilated. The aim of the code of practice is to ensure that historic stone and slate roofs are cared for and conserved effectively. Beyond that, it is hoped that it will raise awareness of the importance of vernacular roofs and details, and encourage more recording and research so that lasting records of these important traditions are built up. In time, they may well provide irrefutable evidence that these techniques and materials do perform well and are entirely suited to modern-day living. Chris Wood is chair of the IHBC education, training and standards committee. Now retired, he was formerly head of building conservation and research at Historic England. He was the main author of the Roofing volume in the English Heritage Practical Building Conservation series. Penmaen Cottage was carefully studied and recorded before it was repaired. Videos showing the work can be seen at http://bit. ly/4eJbbrQ. The roof had no underlay, and allimportant features such as the singlecut valleys have been retained. The roof still has no felt and does not leak. (Photo: Terry Hughes)
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