Abstract: A method of constructing a waterproof layer on a roof deck includes applying an array of coverboards covering the roof deck and a water impermeable membrane. In a leak detection method, an electrical potential is applied between a conductive detector on top of the membrane and a conductor below the membrane such that current flows between the conductor and the conductive detector through moisture or liquid in any leak in the membrane. Each coverboard comprises a base layer of an electrically non-conductive support and insulating material with an upper surface which has laminated thereto a facer sheet material which is formed of an electrically non-conductive material which can be fibers in a binder with an electrically conducting material mixed into the binder.