Abstract: A building roof structure includes a roof deck having a first fire-retardenat layer affixed to and extending at least partway across at least one of the top and bottom surfaces of the deck. One or both of the thermal insulating member and a second fire-retardant layer are disposed upward of the roof deck and its affixed first fire-retardant layer. A layer of waterproof material is disposed atop the thermal insulating member or the second fire-retardant layer. Preferably, the roof deck and first fire-retardant layer are separated from the remaining layers by a moisture impermeable membrane. The preferred first-retardant layers include perlite, Kaltherm or other siliceous material disposed in a resin binder, or gypsum boards. The thermal insulating member is preferably a foamed urethane, while the waterproof layer is an elastomer. A method for constructing the disclosed roof structure is also disclosed.