By Ben Stuart
Roofing solutions might not top the bill as the most glamorous part of a building, but get it right and they can be as memorable as any other element. Think of Wilkinson Eyre’s retractable engineering genius at Wimbledon or any one of Zaha’s sinuous structures.
But first and foremost the roof has to be functional, could we even argue here that form HAS to follow function? Alongside the aesthetics, a roof primarily has to be watertight, it also has to be well insulated to reduce energy consumption and in the case of 5 Broadgate – and the majority of commercial buildings – it has to be robust enough to hold a whole lot of plant equipment that forms the hidden engine of the building.
5 Broadgate is a concrete decked, steel framed construction with a large, flat roof, virtually the size of a football pitch. ‘Hot melt’ roofing is often the go to solution for projects of this nature – whereby bitumen is heated to melting point and applied in two thin layers, with a reinforcement layer between. British Land has used hot melt on the majority of their buildings on the Broadgate estate to date, even as far back as the first buildings in 1984, so they have first-hand experience of its reliability and durability.
One of its primary benefits over alternative solutions is the speed with which it can be applied. On a project of this size, many of the construction packages are deliberately overlapped in order to accelerate the process. With a hot melt solution a second layer can be applied almost immediately onto the first, tested for leaks and the insulation installed. This was an important advantage because it allowed for the plant-supporting concrete overslab to be laid fairly quickly, a crucial factor on a site that’s home to 1,000 construction workers and over 700 tonnes of plant.
But it’s not a panacea – a hybrid solution with cold plastics was employed on several tricky details where the membrane was penetrated. And although hot melt is 50 per cent recyclable, it’s not the most sustainable solution on the market.
Creativity in roofing materials is still needed – even if it is purely for function rather than form – certainly if waterproof concrete or a cold plastic solution is advanced enough to bring down the cost and timescale factors, they’ll undoubtedly take the place of hot melt as the go-to-roofing-solution for buildings of this nature.