Preserving China’s roofs: insights from Yangxin Hall’s centuries-long battle with water infiltration

This study examines the historical water leakage in Yangxin Hall, also known as 养心殿, located within China’s Forbidden City. Yangxin Hall encountered roof leaks from the 1700s through at least the end of the Qing Dynasty. By reconstructing the history of leaks, analyzing repair methods, and investigating architectural modifications, insights are provided into the building’s long-term water management challenges. The present research considers factors such as design modifications, material degradation, thermal stresses, and environmental influences. The findings reveal complex interactions between original design elements and later additions, particularly in the Tiangou area, which impacted the building’s water management capabilities. This analysis suggests that the flying rafter underneath the extended roof connection carries a load that exceeds its designed capacity, causing structural movement and deflection within the wood frame. Through cracks caused by the movement of the flying rafters, moisture penetrates the internal wood structure, which is the most probable reason for the rainwater leakage. These findings provide guidance for preventing and remedying rain leakage in gable and hip roofs in ancient Chinese architectural structures. The relevance extends beyond the context of Yangxin Hall and can contribute to the preservation of different architectural forms and structures in ancient Chinese history.