The Thames-side site posed several engineering problems: the foundations, the need for a fire-resistant structure, the desire to use reclaimed land for the terrace and the provision of building services such as heating, ventilation and drainage.

It has been said that the Houses of Parliament is the first building in which the services provision materially affected the design.

To deal with the foundations and terrace, a 920ft long coffer dam was constructed in the river to the design of Walker & Burgess. It remained in position until 1849. The outer wall was made of a double row of piles with puddled clay between.

The river wall is 7ft 6in thick at the base and 5ft thick at the top. The terrace is made of 26,000 cubic yards of mass concrete. The building sits on yet more concrete: a 7 acre raft with an average thickness of 5ft and thicker under the towers.

The three vertical elements — Victoria Tower, Central Spire and Clock Tower (housing Big Ben) — were governed by ventilation considerations.

The basement is constructed in brick and feature groined vaulting. The floor and seating in both Houses is supported on cast iron columns and raking girders. The pitched roofs are constructed with cast iron plate-clad trusses screwed to the rafters.

The roof of the Commons was replaced after it was destroyed in WW2.

The one surviving part of the Palace of Westminster -- Westminster Hall, originally built at the end of the C11th and rebuilt in 1394 — forms part of Barry's complex.

Architects: Sir Charles Barry and A.W.N. Pugin
Contractors: Henry & John Lee (coffer dam) and Grissel & Peto (building)