How did the tailiang system shape the roofs of traditional Chinese buildings?

The tailiang system, also known as "terraced beams" or "beams-and-columns," is a fundamental structural method in traditional Chinese architecture that defines the shape of a building's roof through a flexible, stepped-up framework.1

In this system, a series of elevated tie beams are stacked transversely across the building. These beams are sequentially shortened as they rise, alternating with vertical struts that support the roof purlins and the main ridge beam. This gable-end framework allows for significant control over the roof's profile; by adjusting the proportions of the vertical rise and horizontal span, architects could create various silhouettes, ranging from the low, straight roofs common in northern China before the Song dynasty to the increasingly elevated and concave curves seen in later dynasties.1

While the tailiang system provides a standardized approach to roof construction, it is distinct from the chuandou system, which uses tall, thin columns along the gable end to support the roof. In prominent buildings, the tailiang framework is often moved inward and may be partially or completely masked by hip-and-gable or full-hipped roof designs.1