Chapel Walks

Just because you can, doesn’t mean you should – Balancing pragmatism with ambitious design

Manchester’s Chapel Walks project is set in the beautiful grade II listed building currently occupied by Sam’s Chop House. Brimming with history, the structure was built in Victorian England with several 20th-century alterations made due to damage sustained in WW2.

renaissance client Investream were looking to transform the characterful location into a tastefully renovated office development. With a fantastic central location and a deft touch applied to the heritage structure, the offices would be sought after by anyone eager to be in the hustle and bustle of the UK’s second city.

As with all heritage projects, every change made to the structure had to be carefully considered. At the Chapel Walks project, there were many potential ways to proceed, including the potential addition of extra floors and an accessible terrace.

While these highly ambitious designs were achievable in theory, were they necessarily appropriate given the building type and its rich heritage?

An ambitious plan for a tricky site

At the outset of the project, we worked with our client to understand their goals and aspirations. We delivered several options, outlining the different structural alterations that could be made. With plans ranging from a structurally minimalist, high-quality refurbishment to an expansive new airspace level and accompanying terrace, there were many varied directions to take the project.

Investream decided to go with the latter option, adding aspiring new levels to the structure. The renaissance team set to work investigating the inner workings of the building and doing the leg work required to bring the client’s vision to life.

This exercise gave us a crystal-clear picture of what would need to be done to accomplish the plan.

We developed a uniquely engineered solution by providing a diagrid as a transfer floor plate to distribute loads and manage building settlement. This allowed loads to be evenly distributed, providing a theoretical solution which could be practically delivered. The challenge then was to work through each of the risk items to verify the theory with fact!

Challenge 1 – The potential for disruption

The first challenge was the need to install only 2 new columns that would support the excess load of the additional levels. While additional columns are not a challenging factor on their own, the situation was complicated by the fact that Sam’s Chop House was at that time intended to be in operation on the lower ground floor of the building.

Although not an insurmountable challenge, the installation would’ve provided a significant operational disruption to the hospitality outfit.

Challenge 2 – The ground quality of the lower ground floor subslab

To support the load of additional stories, we’d need to do foundation work in the lower ground floor area. The site investigations uncovered poor-quality ground conditions at the lower ground floor level. 2-inch thick stone slabs covered a large quantity of historic demolition rubble, meaning any structural interventions would be severely hampered.

This added to the challenge of accessing the machinery needed to make new structural supports for the additional floors and associated costs and logistics of implementation.

Challenge 3 – The ground conditions presented problems for the existing walls

After digging trial pits to investigate the geotechnical ground conditions for the existing walls, we found that they were founded on poor-quality strata. The addition of the new structure and the additional load it would’ve put on the walls coupled with these ground conditions meant the building fabric was at risk due to differential settlement which would be difficult to control without extensive grand improvements.

Even though the settlement could be managed and controlled, given the ground conditions encountered, the likely outcome was that these voids would prove excessive the façade of the building would experience differential movement. Given the Grade II Listed status of the building, there was a material risk that its heritage would be impacted by the proposals.

Challenge 4 – The piers of the existing walls were hollow

Because we were looking at putting additional levels on the building, the piers of the perimeter walls would need to support the extra floors required. In theory, given the size of the piers, they had the capacity. However, our investigations of the building fabric uncovered that these piers were no solid.

This void feature is a known feature in some Victorian buildings with the voids acting as flues for smoke or gas. From a structural perspective, it reduced the capacity of the piers. For them to take a larger structural role in the building, we would need to enhance their capacity.

This would require filling them with limecrete, a material similar enough in nature to the brick piers such that it wouldn’t create structural issues. However, there were practical issues associated with engaging both the existing masonry and new infill as a composite section.

Challenge 5 – The roof and chimneys

The roof of the building presented several challenges to consider before adding additional levels. For one, the perimeter of the building was relatively irregular and would be tricky when trying to tie that in with the new floor level.

Secondly, there were three chimneys in the centre of the building that would need to be carried upwards to the new top level of the building. This presented a number of heritage challenges in providing a solution which was sympathetic and complimentary, whilst also managing the additional loads.

Our approach to the challenges

Whilst the plans for Chapel Walks were ambitious, there were solutions we developed which responded positively and provided a pragmatic response to the challenge. However, the existing onsite conditions presented additional challenges which started to tip the balance in terms of engineering pragmatism and commercial viability

Truly understanding the makeup of the current building and researching its history put us in the best position possible to understand what it would take to make the visionary plans a success. These investigations ultimately revealed that there was little if any spare capacity in the building to do what was proposed without the application of additional interventions. While these challenges weren’t insurmountable, they did bring with them certain levels of risk and associated cost for the developer.

The end result

In the end, this was a case of “just because you can, doesn’t mean you should”. Our client concluded that the plans for new levels were just too prohibitive to pursue and instead opted to go for a pragmatic high-quality refurbishment with minimal structural changes.

As with many heritage projects, the building itself often directs you to do what’s best for it and is informed by the factual data you collate through investigation. There were solutions which could be implemented to respond to each of the challenges. However, on this occasion, just wasn’t the best thing for the structure or the developer.

Client: Investream
Location: Manchester