R. C. DE VEKEY Building Research Establishment, Garston.

The paper covers some of the history of the development of wall ties and cavity walls in Britain, the research which has established the performance requirements and characteristics of wall ties and the work towards a performance standard for ties started at the Building Research Establishment around 1979 in response to the need for cheaper designs for the more durable stainless steel ties. This is now the basis of DD140:Part 1:1986 for testing of wall ties and Part 2: for specifications of wall ties. These DDs include plastic-based ties and ties for timber frame structures in addition to metal ties. Before the DDs are accepted as BS it is hoped to develop the specifications to deal with other ties such as dovetail-slot, steel frame and replacement ties. Factors relevant to the specification of such lies are discussed.