CLASPED PURLIN ROOFS are found in many of Surrey's roofs; it was almost unrivalled as a roof type in the smoke bay period of construction, c1550-1590, and continued in use to the end of the timber-frame tradition and beyond. In mediaeval examples wind braces were used and the principal rafters were wider below the purlins to house the bottorn end of the braces. After 1550 the number of windbraces in a house was slowlv reduced, so that by the chimney period some houses had none at all (although they remained in use in barns). The positions of the windbraces is important to understanding the ground plan. In mediaeval hall houses the braces are generally symmetrically arranged in the hall where they served in part for decoration. Conversely, windbraces are seldom found within a smoke bay, presumably for fear that they should catch alight (or perhaps because all houses which did have them in the smoke bay did burn down!)
The clasped purlin roof is part of a larger set of roof types called through purlin roofs, which includes those with purlins trenched into the top of the principal rafters. The latter form occurs in some Victorian church roofs and Victorian barns and houses but is not vernacular to Surrey. The purlin in Surrey is "clasped" by the collar or raking queen posts against the underside of the principal rafter.