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RCI December 2017

PITCHED ROOFING Keeping the tradition Allan Liddell, of CUPA PIZARRAS, says Scottish roofs are recognised for their distinctive, uneven surface and the use of natural slate tiles in diminishing courses. Traditionally, the high quality grey slates from the Ballachulish quarries were used. However, the quarries were closed in the 1950s, which presented a new challenge to architects and roofing contractors working on re-roofing heritage sites. Here he offers his view on a solution to this problem While some Scottish quarries produced slates in standard sizes, most produced the material in random sizes and thicknesses to ensure the most efficient use of the quarry output. This led to the practice of laying the material in diminishing courses also known as random roofing. Here the roofing is laid with the largest tile at the base of the roof with the smaller ones laid nearer the ridge. The roofing was then fixed in place using a single nail in the centre of the slate head. They were then trimmed at the shoulders of the head to make it easier to move the product aside to access any that were broken or damaged. The pattern of a Scottish slated roof is dictated by the size of the tiles and although it has a distinctive character, this varies from building to building. Preserving heritage Scottish heritage preservation is of great importance so when re-roofing heritage sites, it is key that the same unique look is achieved. Care should be taken to match as far as possible the dimensions, thickness, texture and colour of the original roof. It is also important that the original pattern is replicated as much as possible by using the same number of courses, sidelap and treatment to elements such as skews and dormers. In fact, city planners in Scotland will often still stipulate the use of diminishing courses on these sites. Modern slate as a replacement As no Scottish slate – such as Ballachulish – has been produced for over 50 years, sourcing suitable replacements for use in repair or re-roofing work can be challenging. The issue with modern versions is that it is usually produced in set sizes, and while salvaged or reclaimed Scottish product may be available in some instances, it is scarce and costly. Alongside this, there is also the issue that according to BS 5534, when it comes to fixing the tiles to roofs in Scotland, it is now recommended to do so with two nails. This is due to the extreme weather conditions of this area and the fact that modern versions are often lighter than what was used historically. However, this isn’t in keeping with the traditional look that is so often seen with the roofs of Scottish heritage buildings. Replicating Scottish slate Despite many modern options being incompatible with the needs of the Scottish heritage market, there are producers that offer the material in a range of sizes and in the required weight. These options allow for diminishing courses as well as the use of just one nail making them the ideal replacement product. Our Random format, which uses Heavy 3 natural tiles, is a great example. Heavy 3, which has the same colour, texture and markings as Ballachulish, is specifically for those involved with heritage builds in Scotland with the Random version providing the option of diminishing courses. What’s more, its true heaviness, thanks to a thickness of 7-8mm, gives it the perfect strength to withstand the Scottish weather, making it ideal for using the traditional fixing method of single nail fixing. Modern slate provides a great finish for so many projects but for Scotland, with its very specific aesthetical and weight requirements, especially when it comes to heritage buildings, many modern options can’t fulfil these needs. However, thanks to products that have been specifically created for the Scottish market, re-roofing these buildings in keeping with their heritage is now possible and in a cost effective way. This allows roofing contractors and architects to meet stipulations set by city planners simply and efficiently while allowing the preservation of Scottish heritage. www.cupapizarras.com/uk History of slate roofing in Scotland “The pattern of a Scottish slated roof is dictated by the size of the tiles and although it has a distinctive character, this varies from building to building” Above: Tobermoy church Left: Balhousie Castle


RCI December 2017
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