While the application of uPVC single-hung or double-hung windows in renovations of buildings with historical importance are technically possible, many of these renovations require much higher performing window designs including those that are commercially rated. Many PVC single and double hung designs do not attain commercial ratings and would therefore be unsuited to these applications.

The REHAU System 4500 tilt & turn window designs achieve excellent structural, thermal and sound insulating performance, can be fabricated in large sizes, require fewer profiles to stock and in general have more robust design properties than most hung-sash windows.

Meant for residential as well as commercial uses, the REHAU System 4500 is a popular choice for commercial as well as institutional applications by being able to have limited ventilation possibilities for the building occupants. The design of the hardware mechanisms can be configured to limit the sash operation to tilt only, allowing safe and secure ventilation at the top, making the window safe for use on upper floors of buildings. In this mode, the mechanisms can be unlocked by maintenance or janitorial personnel for cleaning or general maintenance.