This study began in November, 1960 and involved studies of all bats living within one large and complex roof. Furzebrook House, built in 1885, was of brick with hollow walls and a black slate roof. The roof consisted of 9 distinct sections comprising some 385 m³ of which 60 % was accessible for searching. Eight species were caught in these accessible regions and because Plecotus spp. were the most numerous, they became the chief study. The study became more significant when Plecotus austriacus (Fischer) (first described by Bauer, 1960), was identified in the roof. Detailed descriptions of the two English Plecotus have already been published (cf. Stebbings, 1967). The aim of this report is to present evidence that might suggest reasons for the distribution of the two Plecotus in northern Europe, and particularly their northern limits.