The Elizabeth Tower is one of the UK’s most recognisable landmarks. Completed in 1859, the 96-metre structure is more commonly known as Big Ben, after the famous 13.5-tonne bell that is housed in the Tower and sounds the hour across London.
Throughout its 160-year history, the tower has endured two world wars and witnessed many of Britain’s most significant events. However, decades of exposure to pollution, weather and wartime damage had all taken a toll on the building, calling for a major conservation effort.
Collaborating closely with the Parliamentary In-House Services and Estates (IHSE) team, architect and contractor, our structural and heritage engineers played a vital role in this complex refurbishment, applying our extensive expertise to safeguard the tower while respecting its architectural heritage.
The most extensive restoration in the Tower’s history
When the Parliamentary IHSE team first commissioned the refurbishment in 2012, it was anticipated that only minimal, routine maintenance would be required. However, after closer inspection, it quickly became clear that significant repairs were needed. This was especially true for sections of the structure damaged by bombing during World War II, which were never fully repaired.
Ultimately, the 5-year restoration programme amounted to the largest in the tower’s history. The works included: repairing and redecorating the cast iron roof, clock faces and high-level metalwork, waterproofing the belfry, repairing the external stonework, installing a new lift, providing a new fire alarm system, establishing conservation heating, and undertaking a comprehensive systems re-servicing.
Overcoming complex challenges
Working on a structure of this historical importance required more than just structural expertise. The Tower’s status as a Grade 1 listed building meant that every aspect of the work needed to balance preservation with modern safety standards.
For example, one of the most complex tasks was the erection of a 98-metre scaffold system around the tower, for which we prepared the concept design. This temporary structure, which took six months to assemble, allowed for the safe restoration of both the roof and stonework.
Another challenge we faced was the limited documentation of previous repairs and wartime damage. Without detailed records, our engineers had to rely on information sourced from old photographs and newspaper articles of previous restoration works undertaken in the 1950s and 1980s.
In addition, a 3D point cloud scan of the building was undertaken using drones. This scan was used to develop a full BIM model of the tower, which was then used to coordinate all further design development.
Working within a UNESCO World Heritage site further complicated the project. Surrounded by equally protected historic buildings, extreme care was required to avoid damage during construction.
Bringing together contractors and artisans from across the nation
One of the project’s key successes was the collaboration between large contractors and skilled artisans from across the UK, whose combined expertise delivered exceptional results.
For the 30-metre cast iron roof, thousands of intricate iron components were carefully removed, and restored or recast in specialist workshops across the country. This extensive effort ensured that as much of the original material as possible was retained.
Skilled stonemasons also replaced over 700 masonry pieces, working from a temporary workshop established at the base of the tower. One of the more challenging tasks was sourcing replacement stone for the weathered limestone cladding. With the original Victorian-era quarry no longer in operation, the design team identified a new quarry that could provide a similar stone. Each piece was then hand-carved to blend seamlessly with the tower’s original façade.
For the past century and a half, there has only been one way up and down the tower – a single, narrow stone staircase. To facilitate easier maintenance and emergencies, a lift was constructed in an existing ventilation shaft. By collaborating with small UK-based manufacturers and a steel contractor, we were able to develop a design to support the lift frame using standard steel section sizes, rather than having to fabricate bespoke supports. This significantly reduced the cost of the lift installation.
Preserving history
As part of the restoration works, we carried out a detailed analysis of the delicate cast-iron clock faces. Through this work, we were able to justify that, even though there were some cracks in the intricate iron frame, structural repair of the clock faces was not required. This not only saved time and reduced costs, but it also ensured that all of the historic fabric of the clock faces was retained.
We also worked with SPS Technologies to design a new “crash system” to protect the electrical equipment in the basement of the tower in the event that one of the heavy cast iron weights that drive the clock – the heaviest of which weighs 1.5 tonnes – should ever break free and plummet down the weight shaft (a 50-metre drop).
All information gathered during the restoration has been integrated into a digital asset register and recorded in a full BIM model of the tower, ensuring that future conservation teams will have detailed records of every component.
An exemplary approach to heritage restoration
The Elizabeth Tower refurbishment is a strong example of how modern engineering and traditional craftsmanship can come together to preserve a national icon.
To mark the completion of the refurbishment works on the Great Clock mechanism, Big Ben chimed on Remembrance Day (13 November 2022) – the first time that Big Ben and the quarter bells had chimed since the bells were silenced in August 2017.
Now complete, our work has not only protected the tower from further deterioration, but also improved its future resilience, enhanced accessibility and simplified routine maintenance – securing its place as an iconic landmark for generations to come.