From the 1760s the strict conventions of Palladianism were challenged and then modified by a new breed of professional architects of whom the greatest were Robert Adam (1728-92), his younger brother James (1732-94), Sir William Chambers (1723-96) and James Wyatt (1746-1813). Robert Adam was the leading force in creating a new style, spending several years abroad and examining sites of antiquity at first hand. He denounced the eternal repetition of the same traditional classical elements and brought a greater degree of flexibility to the interpretation of classical architecture. Inspired by his study of the ruins of Diocletian’s Palace in Dalmatia, he also introduced a new range of decorative motifs. The result was a new architectural style which is generally known as Neo-classical or even simply as ‘Adams style’. It was characterised by buildings with light, elegant lines unbound by strict classical proportion. Adam treated ornament freely – introducing delicate swags and ribbons into his interiors which were painted in delicate greens and blues, lilacs, dove greys and faint yellows. The fan light was a prominent feature of Adams style. They were at the peak of their popularity between 1760 and 1780 when they consisted of a complex pattern in iron and lead typically of spokes radiating outwards from a central floret and decorated with swags and garlands. Windows were taller with thinner glazing bars. Lower down the social scale, smaller houses were built to precisely the same proportions only on a reduced scale. The distinctions were codified in the great Building Act of 1774 which aimed at preventing poor quality construction and reducing the risk of fire. By the Act, houses were categorised or ‘rated’ according to value and floor area. Each rate had its own code of structural requirements as regards foundations, external and party walls.