The Guildford Formation and its influence on residential construction

The Western Australian residential development industry has evolved practices for the preparation of subdivisional areas over Guildford Formation soils, which require Lot classifications to achieve an ‘A’ or an ‘S’ classification under AS2870-1996, and which require rainfall other than roof runoff, to be managed substantially within the individual Lots rather than by immediate discharge to Local Authority street drainage systems. This paper discusses the current procedures and notes that both issues (soil reactivity and the subsoil drainage necessary to ensure immediate surface runoff to street drainage does not occur) must be considered concurrently. The current practices were developed at an earlier time; with a maturing of the Western Australian engineering market and the development of smaller Lot sizes this paper proposes that it may be time to review the regulatory conditions that are driving current practices.