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Overcoming the challenges of the restoration of World Heritage Sites

  • Posted on 13th July 2015
  • Category: General

This article appeared in the July 2015 issue of Building Engineer.

World Heritage Sites – often ancient buildings of special cultural significance – are some of the most important buildings to conserve and restore, yet some of the most challenging.

Their age and design can mean these sites are difficult to work on, as so many things need to be considered to ensure that there is no damage or negative impact on the building.

Mark Turner, director at Patrick Parsons Consulting Engineers and a conservation expert, discusses the challenges involved and the restoration project he has been leading at the historic Durham Cathedral.

Durham Cathedral, an 11th century Norman building, is one of the finest in the country and was one of Britain’s very first World Heritage Sites. Patrick Parsons’ skilled engineers have provided structural engineering design services to the Cathedral for more than 40 years, with an ongoing relationship with the Estates Office that has led them to work on a number of projects and commissions located within the grounds.

This work involves the ongoing engineering and restoration works to the Cathedral and associated buildings, in order to help preserve the quality of one of the North East’s most recognisable and cherished buildings.

In 2011, Mark Turner and his team were appointed as civil and structural engineers for a £10 million project Heritage Lottery Fund; the engineering phase due to be completed late summer 2015. The work is part of a multiphase development project called Open Treasure, this current phase involves the creation of stunning exhibition spaces in medieval buildings around the Cathedral Cloister. The project incorporates new build elements   providing enhanced visitor facilities and involved sensitive restoration from the team.

Restoring this type of building, without causing irreparable damage or resulting in inappropriate additions, is a challenge faced by heritage experts across the country and one which conservation expert Mark Turner has to consider on a daily basis.

As a chartered civil and structural engineer and expert in the assessment and refurbishment of existing structures and in particular, the conservation of historic properties, Mark has worked on some of the most renowned heritage projects in the UK.

Mark explained: “Admission will be charged for entry to the new exhibiton spaces, with income  contributing towards the ongoing conservation of the Cathedral and its collections. Combined with  additional revenue through ancillary spending and donations, this income will ensure that  access to the Cathedral Church itself remains free.”

During the team’s work on this project, there have been many changes due to the development of the design as it has progressed. These have included multiple re-designs of various structural elements as a result of architectural changes.

The team from Patrick Parsons working on the project includes senior structural engineer Leon Walsh, and technicians Andy Turner and Joanna Pullan as well as Mark himself – all of whom have years of experience in historic buildings and conservation.

Mark said: “The Open Treasure project is the largest investment in the Cathedral in modern times and because of the fluidity of this type of historic project, we have faced many challenges and design changes. This is due to the exposure of archaeology and uncovering of areas on site that have required amendments to the structural design, in order to provide the best and most sympathetic result without affecting the historic structure.

“All structural elements specified which are built into the Cathedral, such as lintels and pad stones, are sympathetic to the existing structure using traditional materials. New connections into the existing building have been kept to an absolute minimum with new steelwork using existing pockets, and steelwork has been designed to cantilever where support could not be taken from the existing structure.”

The project involved taking out a building comprising 1950s infill situated between two medieval buildings.  A stunning new state of the art two story gallery space is being built.   Steel sizes for this space  have been kept to a minimum as access for the steelwork was via the courtyard by mobile crane, although spans of 10m were required to support the new roof. Membranes have been laid below new concrete to protect the historic sub floor and to allow easy removal in the future if required.

Mark continued: “Other challenges involved designing the new structure to allow the passage of services within floor zones without affecting the existing building.  The design of plenum and floor structure arrangement to control the air flow in the Great Kitchen exhibition area – where the 7th century St. Cuthbert’s coffin will be housed – was difficult due to the octagonal shape of the Great Kitchen.”

During the archaeological excavations and site preparation there were a variety of interesting finds. Thousands of animal, fish and bird bones were excavated in the Covey area next to the Great Kitchen, which gave a good insight into what the monk’s diet consisted of and how the food was prepared.

Additionally, newspapers from 1880 were found underneath a book case in the Monks’ Dormitory whilst it was being dismantled, and whilst removing plaster from one of the walls in what is to be the Collections Gallery, part of an arch was discovered. This was found to be of historical importance, so will be retained and made into a complete arch again to become a feature in the exhibition.