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Repairing a cupola

Peter Scott Aiton sets out the complex task of repairing the cupola at Orbital House in East Kilbride

When buildings are designed, there is often the desire to create something different or at least involve a feature that will make the building stand out from the crowd. This was most certainly the case when the iconic Scottish headquarters of British Energy was built in East Kilbride. 

Orbital House is shaped like a crucifix on plan and the four wings are centred on an impressive four storey atrium with a fullsized glass cupola. While the glazed cupola was an exceptional product for the early 1980s, many of the component parts had reached the end of their useful life. 

The cupola had been maintained and patched to try and extend the value that could be extracted from it, but it got to the point where full replacement was the only viable solution. 

Technology and manufacturing of bespoke glazed cladding products has advanced significantly since the 1980s. However, replacing a glazed atrium that sits some 20 metres above the main common space within a fully occupied building is not a simple project. 

As much effort had to go into designing the scaffolding and temporary protection as the cupola itself. 

We designed a self-supporting scaffold tower that ran all the way up the centre of the atrium, with a cantilevered platform to seal off the work area from the building below. This platform was fully protected with Corex sheeting and waterproof membranes to ensure no debris or water could reach the occupied areas of the building. 

Hoovers and wet vacs were left at this level to catch any issues quickly. An external work platform around the edge of the glazed cupola was also needed. 

A scaffold access stair was built off one of the third-floor balconies and a walkway was then formed off the pitch of the slate roof below the cupola. The imposed loads all had to be carefully scrutinised by a structural engineer so as not to overload any part of the building.

Finally, we designed a waterproof cover over the cupola that would prevent excessive water ingress during the works. All sorts of scaffold structures and tin roofs were investigated but finding something that could take the wind load in such an exposed location was not easy. The design team settled on having a bespoke thick waterproof hap made. It was supported by the internal structural steelwork, but we had to draw on our contacts within the competition sailing world to establish the best way to tie it down. Instinct would tell you to tie it tight, the experts’ advice was the opposite. By tying the hap loosely, it allowed the wind to get under it and exit the other side without causing any damage. 

Once we had the site setup arranged, the replacement of the cupola was fairly straightforward. We insisted that the contractor had a site presence 24 hours a day while the cupola was off. This meant that the hap could be supervised and any water ingress cleared up quickly. 

Although cupolas are great design features and allow good natural light, purchasers should be aware of the future liability and prohibitively expensive cost of replacement. The Galbraith building surveying team prides itself on being aware of such wider property implications. This sort of advice is always offered when commissioned to complete building acquisition surveys. Early awareness means that budgets and asset management approaches can be put in place from the outset.