Between 1909 and 1912 the medieval timber roofs over the choir and nave (which were found to be unsafe) were replaced with new oak roofs, under the direction of William Thomas Oldrieve, Architect for Scotland within the Office of Works. The weight of the roof was reduced by the substitution of copper sheeting for lead and slate, and the distinctive green copper roofing on the exterior of the nave and choir dates from that time.[20]