More than any other part of the stadium, the roof - or more precisely, the lack of cover it affords from rain - has come in for criticism. Although a pressure bulge develops over the stadium, reducing rainfall by 30%, complaints forced a rethink as the development progressed. It is the one part of the finished design that appears gauche: the earlier phases of the cantilever roof extend 34m, while the last phase - over the Hogan stand - extends 48m. The overall effect, despite the subtleties of the design which responds to orientation by varying the amount of glazing in each canopy, looks clumsy.
"In retrospect, we wouldn't make that decision again," McMahon (architects) admits. Back in 1992, the GAA believed they couldn't afford the extra £2m which would have been added to the construction cost for every extra metre of cantilever over and above the initial 34m. Now they make that much whenever there's a major championship match.
The huge extra cost was a result of the horseshoe shape and phasing, as the roof of each stand had to be independently stable. The optimum shape for a column-free stadium roof providing full cover is circular or oval, where the front edge of the cantilevered roof can be designed as a compression ring that prevents it sagging. The biggest problem facing a horseshoe cantilever is bending from uplift, however, caused by wind rushing in under the canopy. The longer the cantilever, the greater the strain, and full rain cover would have required the stand to project well beyond the touch line, leaving only the central 40% of the pitch uncovered. Exposing the steel structure above the roof produces the turbulence necessary to prevent uplift of the roof.
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