CONTEXT 185 : SEPTEMBER 2025 15 ROOFING Scottish tradition of slating in diminishing courses. Larger slates were used at the bottom as they were better able to handle large volumes of rainwater that shed down off the roof. The smallest slates were the most robust against strong winds, so it was sensible to fix these closer to the ridge. Smaller slates also allowed for single centrefixings, which made ongoing maintenance and repair easier, as slates could be simply swung to the side to replace any damage underneath. Slates are usually laid in a double lap in Scotland. This is best able to cope with the Scottish weather, but the ratios of side lap to head lap will vary depending on the size of the slates used. Experienced slaters will calculate these proportions at every new course as the size of slates changes. Traditionally, the slates would be laid on sarking boards (rather than batons) to allow for slates of random sizes to be laid and provide more robustness against wind lift. A ‘penny gap’ was left between boards to allow for free moisture and vapour movement. When underlays were introduced, this was to reduce any draughts coming through, rather than replacing a well-calculated side lap to make the roof watertight. Pantiles Clay pantiles have been used in Scotland since at least the 17th century, originally due to Scottish trading ties with the Low Countries, until pantiles started to be made locally in the 18th century. The range of colours from local clay variations and distinctive undulation add their own specific character to the roofscape. The properties of clay change depending on the type of deposit they are formed from, which varies both the colour and durability. Unlike slates, pantiles are typically laid in a fixed-gauge single lap, where the s-shaped tiles have notches or mitres that fit closely. This distinctive shape means that, when laid correctly, rainwater is directed right down the centre of the tiles and off the roof. Replacing damaged tiles with ones which do not match closely can throw off this line and cause issues with water shedding. Clay ridge tiles would typically be laid in a lime mortar and there would be a lime-mortar skew fillet to ensure that the roof was kept weathertight, but still breathable and compatible with the vapour-permeable clay tiles. In some areas, the bottom courses of a pantile roof are finished in slate. This allows for a gentle easing to slightly flatten out the roof into a bellcast profile. This detailing is useful in more exposed and windy areas as it gives greater protection from the rain at the wall head and helps to prevent damage caused by uplift from the wind. Thatch While the number of thatched roofs has declined dramatically since their heyday, those that remain are an important reminder of their former ubiquity and the aesthetic of Scotland’s community-led vernacular building tradition. Materials varied greatly and changed depending on what was available locally at the time, with a mix of crops such as rye, barley, black oat, and gathered materials like heather, broom, rush, marram grass and bracken. When thatching a roof, a base layer of, for example, a woven web of ropes or timber poles would first be needed to support the thatch. A layer of turf on top was also sometimes added, which could help with the weatherproofing of the roof structure as a whole. The thatching material above would shed water through a combination of surface tension and gravity, directing water over and off the roof edge. It was important that the thatch was applied thickly enough to prevent any rainwater penetrating the roof. Available materials and the type of thatch also led to the development of different finishing details such as those on the ridge and verges, and different methods of fixing, such as using hazel spars or rods, as well as netting (and later chicken-wire). Additional weights such as logs, bricks and stones were also sometimes added, Sarking boards, showing the distribution of nails (Photo: Madeleine Clark) Pantiles at Culross Palace (Photo: Historic Environment Scotland)
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