The oldest surviving part of the Palace of Westminster has been secured for generations through a decade of conservation work.

Completed in 1097 by William Rufus as a Romanesque Hall, the now Grade I-listed Westminster Hall was the seat of government from the late medieval period. For almost 1,000 years, it has hosted state events including coronations, banquets, public trials, and the Queen’s lying-in-state.

Between 2010-2020, DIA and Parliament’s Strategic Estates Team worked on the first non-reactive repair and conservation project at Westminster Hall in a century. Work comprised of three phases: stonework repairs to the north wall and the installation of a stained-glass window in the 14th-century North Window; cleaning of the internal masonry walls and windows; careful conservation of the 14th-century hammerbeam roof and lantern.

The design approach was one of minimal intervention based on historical research, extensive site surveys, trials and investigations. Where appropriate, well-established conservation methods were used. However, the particular conditions of the fabric required innovation, including the use of nano-lime to consolidate carved medieval Reigate stonework and latex poultices containing potassium hydroxide for stone cleaning. Repairs were generally detailed following the historical design, but changes were made to the design of the lantern to improve rainwater drainage.

This research and subsequent work furthered technical knowledge of conservation techniques for Britain. The findings have been incorporated into studies by Historic England on the conservation of Magnesian limestone and by Historic Royal Palaces on Reigate stone, informing the conservation and repair of listed buildings and Scheduled Ancient Monuments across Britain.

Westminster Hall remained open to the public throughout the construction stage as an events space and main entrance to the Houses of Parliament to recognise the democratic right of citizens to visit Parliament.

In consultation with the building users, the House of Commons Education Department and Visitor Services identified opportunities for visitor and public engagement, therefore temporary interpretation was installed throughout the three phases of work to contribute to the visitor experience. This also benefited school groups who visit daily.

The project provided learning opportunities for students from the Society for the Protection of Ancient Buildings (SPAB) and apprentices from the Building Crafts College. The latter worked alongside DBR stonemasons, providing a rare opportunity for the apprentices to work on gothic revival masonry.

• Client: UK Parliament Strategic Estates 
• Structural engineer: Alan Baxter ltd 
• Contractor (phase 1): Skillington Workshop 
• Contractor (phase 2): DBR (London) ltd 
• Contractor (phase 3): Mitie Projects 
• Masonry sub-contractor (phase 3): DBR ltd 
• Joinery Company no.1 (phase 3 hammerbeam roof and lantern): Dolmen Conservation Carpenters 
• Joinery Company no.2 (phase 3 lantern vaulting): Sands & Randall Carpenters 
• Wood supplier (phase 3): Dolmen Conservation Carpenters 
• Window glazing/leaded lights (phases 1 and 3): Reyntiens Glass Studio 

• Europa Nostra Awards: Conservation and Adaptive Reuse category (2024)
• Wood Awards: Restoration and Reuse category (2023)