CONTEXT 185 : SEPTEMBER 2025 25 ROOFING Terry Hughes is an independent and Historic England slate and stone roofing consultant, and the UK slate industry’s representative on UK and European technical committees. He is grateful for contributions to this paper from Chris Wood and Richard Jordan, and to Welsh Slate Ltd for support in obtaining special slates. Slope 5B. The original random slating near the eaves was renewed with similarly thick slates. These tilted the tally slating above to ensure that the slates rested on the head battens. In anticipation of worsening storms, the resistance of headpegged verge slates was improved with tee nails. These fix the slates at a lower position into the counter batten. All the slating except Slopes 10 and 11 was torched with wellhaired 1:1 air lime:sharp sand mortar, further stabilising the slating and preventing condensation drips on to the mill machinery. valley a doubled slate was laid to tilt the slating, and turn water away from the verge and into the valley. At the other verges the slating was tilted by doubling or lifting it on counter laths or battens. Wind resistance The two early systems on Slopes 2–4 and 6 and the reslated Slopes 1 and 8, were renewed by pegging to riven laths and head bedded in 1:1 air lime: sharp sand mortar. This supports the slates’ heads, locking them together with surrounding slates, so they share fluctuating wind loads as they ripple across the roofs. At the eaves where there were no wall plates, a doubled layer of mortar bedded under eaves slate, was reinstated. This levelled the wall head and provided tilt, ensuring that the overlying slates’ heads were on the battens. Similarly, on Slope 5, when the slates had been replaced with tally slates, they were laid on to the original random slates at the eaves. Replicating this with similarly thick random slates provided tilt to the tally slates. At the verges, the overhang was reduced slightly to reduce wind exposure. To improve the resistance, tee nails were used at every third or fourth course, fixed into the counter laths or battens. All the slating, except on Slopes 10 and 11, was torched with well-haired 1:1 air lime: sharp sand mortar, further stabilising the slating, and having an additional purpose, to absorb condensation. Drips of condensation from cold slates would wet the flour, clogging the mill stones and machinery. Slopes 10 and 11 were not torched originally or in the reslating, to allow moisture from the corn drying to ventilate through the slates. Originally there was also a vent at the ridge, yet to be reinstalled, for the same purpose. Completion Work started in September 2024 and was completed by Christmas, with the original vernacular and modern techniques applied throughout and using authentic slate types on each slope. The techniques’ effectiveness was demonstrated during Storm Darragh when only Slope 1 had been slated – the opposite slope was effectively open to the 96mph wind measured in Aberdaron. Not a single slate was disturbed, although other roofs nearby were damaged. Later the finished slating was completely unaffected by the severe Storm Éowyn in January. Further reading English Heritage (2005) Stone Slate Roofing Technical Advice Note, (revision including metamorphic slates in preparation) Historic England (2013) Practical Building Conservation: roofing Emerton, Gerald (2017) The Pattern of Traditional Roofing Hughes, Terry (2023) ‘Surveying vernacular roofs’, Context 178, December Historic England (in preparation) Code of Practice for Slate and Stone Roof Repair and Conservation
RkJQdWJsaXNoZXIy MzI0Mzk=