The earliest surviving oast house is at Golford, Cranbrook near Tunbridge Wells. It dates from sometime in the 17th century and closely mirrors the first documentary evidence on oasts soon after their introduction of hops into England in the mid 16th century. Early oast houses were simply adapted barns but, by the 18th century, the distinctive tall buildings with conical roofs had been developed to increase the draught. At first these were square but around 1800 roundel kilns were developed in the belief that they were more efficient. Square kilns remained more popular in Herefordshire and Worcestershire and came back into fashion in the south east in the later 19th century. In the 1930s, the cowls were replaced by louvred openings as electric fans and diesel oil ovens were employed.