A roof for a computer rack aisle is provided. The roof has a canopy that may be flexible and/or fire-resistant. The canopy has a retracted position and an extended position. In the extended position the canopy may cover the top of an aisle between two computer racks, while in the retracted position the aisle can be uncovered. A canopy retractor is provided to move the canopy from the extended position to the retracted position when a predetermined condition is met. The canopy has first and second lateral edges that are slidably received within the channels of guide tracks to facilitate the smooth movement from the extend position to the retracted position.