Pearce's design was revolutionary. The building was effectively semi-circular in shape, occupying nearly 6,000 m2 (1.5 acres). Unlike Chichester House, which was set far back from Hoggen Green, the new building opened directly onto the Green. The principal entrance consisted of a
colonnade of
Ionic columns extending around three sides of the entrance
quadrangle, forming a letter E (see picture below). Three statues, representing
Hibernia (the
Latin name for Ireland), Fidelity and Commerce (later carved by
Edward Smyth) stood above the
portico. Over the main entrance, the royal coat of arms was cut in stone. According to Patrick Wyse Jackson, curator of the Geological Museum at
Trinity College Dublin, the granite used in the central 'piazza' of the Parliament House may have come from the Baltyboys quarry close to
Blessington, where contemporary documents show that one William Borrowdale was paid
£6-16s-2d for 'mountain stone' on 24 December 1729. It is known that granite quarrying had been taking place in west
Wicklow since the early 1700s from several openings at Baltyboys, and "from 1740 in more significant volumes at Woodend and Threecastles nearby and then from
Golden Hill." The Parliament House is also noteworthy for its decorations, which, unusually, were carved from granite as opposed to a more malleable stone. Wyse Jackson notes that "they would have been difficult to produce, on account of the coarse texture of the rock, and so reflect the considerable skills of the stonemasons. It is unusual to find granite so delicately carved". The building underwent extensions by architect
James Gandon, between 1785 and 1789 he added a new House of Lords entrance at the east of the building, facing onto
Westmoreland Street. Unlike the main entrance to the south, which came to be known as the House of Commons entrance, the new peers' entrance used six
Corinthian columns, at the request of peers who wished their entrance to be distinct from the Ionic columns of the main entrance. Over this, three statues by Edward Smyth were placed, representing Fortitude, Justice and Liberty. A curved wall joined the Pearce entrance to Gandon's extension. This masked the uneven joins of some of the extensions, as shown below. The wall, built of
granite was also inset with blind niches. Another extension was added on the west side into Foster Place, designed in 1787 by architect Robert Parke; while matching Gandon's portico, he tried a different solution, linking the other portico to the main Pearce one by a set of Ionic columns in a colonnade. The result was poorly received and when the
Bank of Ireland took over the building, it employed Francis Johnston to create an architectural unity by replacing this set of Ionic columns by a curved wall in line with Gandon's original design. Ionic columns were then added to both curved walls, giving the extensions an architectural and visual unity that had been lacking and producing the building's ultimate exterior. The interior contained one unusual and highly symbolic feature. While in many converted parliamentary buildings where both houses met in the same building, the houses were given equality or indeed the upper house was given a more prominent location within the building, in the new Irish Houses of Parliament the
House of Commons was featured, with its
octagonal parliamentary chamber located in the building's centre. The smaller
House of Lords was given a lesser position nearby. The original, domed House of Commons chamber was destroyed by fire in the 1790s, and a less elaborate new chamber, without a dome, was rebuilt in the same location and opened in 1796, four years before the Parliament's ultimate abolition.
Materials Patrick Wyse Jackson, curator of the Geological Museum in Trinity College, assessed the building in 1993 and noted the following: :
"It has a façade forty-seven metres long with a portico supported by impressive Ionic columns. The building has Calp Limestone rubble walls, which have been faced with Portland Stone. If you look closely at this stone you will find that it is full of shells, predominantly fossils of oyster shells... (The interior) contains a fireplace of black Kilkenny Marble. The Cash Office is floored in a chessboard pattern with slabs of Cork Red Marble alternating with Portland Stone." ==Pearce's design copied==