Architecture news & editorial desk The Council has outlined evidence they say proves that uPVC (unplasticized or rigid PVC) window frames do not pose a significant risk of accelerating the spread of fire on an external wall compared to a non-combustible, or metal, frame. uPVC is an exceptionally energy efficient material that assists with the overall performance of a home. The Council is seeking to modify the Deemed-To-Satisfy (DTS) requirements, with a concession for window sashes and frames from the non-combustibility requirements for external walls of buildings over three storeys. Without a DTS solution, it means that uPVC and timber window frames are unable to be used in some residential buildings of three storeys or more.