In terms of interior design, Number Twenty Nine reflects the dominant architectural and decorative style of the period 1790-1820; the Neo Classical as epitomised by figures such Robert and James Adam and represented in Dublin by fine buildings such as the Customs House and Four Courts by the English Architect James Gandon.
The emphasis of Neo Classical design is on the formal and on the sense in which all of the individual parts of a plan, be it a scheme for a room, or the façade of a building, if properly designed and proportioned will fit together to form a harmonious whole.
By the dawn of the 19th century however, greater variety was introduced into decoration and we see the introduction of a range of new styles into the Neo Classical, including the Empire Style frequently drawing inspiration from Egypt, which was stimulated in part by Napoleon's military campaigns, the Neo Grecian style, illustrated by the Neo Grecian General Post Office designed by Francis Johnston. Evident also at this time was the neo-gothic, which took its inspiration from Northern European architecture of the medieval period and which can be seen as a reaction against the restraint of Neo-classicism. All of these trends can be seen in the pieces and decorative finishes of Number Twenty Nine.
The furniture, glassware, ceramics, and painting on display is mostly Irish from the late 18th century or early 19th century. To meet the rising demand of an expanding Dublin, manufacturers of luxury goods prospered in the city.
Dublin in 1798 possessed at least 25 coach builders, over 30 gold and silversmiths, and nearly 50 cabinet makers , all supplying to the inhabitants of the large mansions found in Merrion Square and Stephen's Green and increasingly to those moving into the more moderate developments in areas such as Mountjoy Square and Fitzwilliam Street Lower.