Paxton's roofing system incorporated his elegant solution to the problem of draining the building's vast roof area. Like the Chatsworth Lily House (but unlike its later incarnation at Sydenham) most of the roof of the original Hyde Park structure had a horizontal profile, so heavy rain posed a potentially serious safety hazard. Because normal cast glass is brittle and has low tensile strength, there was a risk that the weight of any excess water build-up on the roof might have caused panes to shatter, showering shards of glass onto the patrons, ruining the valuable exhibits beneath, and weakening the structure. However, Paxton's ridge-and-furrow roof was designed to shed water very effectively. Rain ran off the angled glass roof panes into U-shaped cast-iron channels which ran the length of each roof section at the bottom of the 'furrow'. These channels were ingeniously multifunctional. During construction, they served as the rails that supported and guided the trolleys on which the glaziers sat as they installed the roofing. Once completed, the channels acted both as the joists that supported the roof sections, and as guttering—a patented design now widely known as a "Paxton gutter". These gutters conducted the rainwater to the ends of each furrow, where they emptied into the larger main gutters, which were set at right angles to the smaller gutters, along the top of the main horizontal roof bearers. These main gutters drained at either end into the cast iron pillars, which also had an ingenious dual function: each was cast with a hollow core, allowing it to double as a concealed down-pipe that carried the storm-water down into the drains beneath the building.