A method of repairing an electrostatic precipitator, including building a temporary support truss assembly, supporting the temporary truss assembly at the level of the hot roof of the electrostatic precipitator, transfeffing the weight of the internal components of the electrostatic precipitator from the upper girders to the temporary truss assembly, repairing or replacing the upper girders of the electrostatic precipitator, and then transferring the weight of the internal components to the repaired or replaced upper girders.