The roof design may look as though it came from the imagination of an architect, but it was the tight limitations of the historic railway site that determined design and specification.
The concrete slab of the London Underground Northern ticket hall formed the base of the site, which meant only limited space for supports. English Heritage and Camden Council did not want the roof any higher than the listed Western Range building and its Grade I listed status meant that it could not be modified to bear any loads from the concourse roof. The designers also had to incorporate the curved Great Northern Hotel to the South, which had been conveniently obliterated by Sir Norman Foster in a previous masterplan for King’s Cross.
The engineer Arup and architect John McAslan + Partners quickly realised that a large spanning half dome requiring a limited number of supports was the only form that would fit the requirements of the site and provide enough space for passengers and retail units. (It’s three times the size of the Sourthern concourse.)
Together they drew up the design for the roof which was supported by 16 tree columns and the funnel. The roof has a diagonal grid structure similar to the the Gherkin, but with beams incorporated to account for the unusual concourse shape.
The roof is covered with 1,012 glazed triangular panels at the perimeter and towards the funnel, but to provide necessary shading the rest of the roof is covered with aluminium cladding laid over acoustic panels. This gives station announcements a rare clarity and reduces ambient noise to a comfortable level.
The curvature of the Great Northern Hotel was not the same as that of the roof, so different gutter widths were used to fill the varying gap between the new and existing structures.