“The Science of Roof Design: How Ancient Architects Knew Best”
Adrian Bejan, a visiting professor in Benevento, Italy, noticed a unique pattern in the local architecture – all the roofs looked the same. Intrigued by this observation, Bejan, an expert in thermodynamics and heat transfer, decided to investigate further.
Collaborating with Pezhman Mardanpour, assistant professor of mechanical and materials engineering at Florida International University, Bejan conducted a study to analyze the heat retention properties of different roof shapes. Their findings, published in the journal International Communications of Heat and Mass Transfer, revealed that certain roof shapes can maximize heat retention.
According to Bejan, the height and slope of a roofline play a crucial role in determining how air flows within the attic space. For roofs with peaks less than three feet tall, the air flows smoothly and uniformly. However, for taller peaks, the air tumbles chaotically, leading to heat loss.
Based on the physics of airflow and heat transfer, Bejan recommends specific height-to-width ratios for optimal heat retention. For roofs with peaks shorter than three feet, the peak should be three to four times wider than it is tall. For taller peaks, an equilateral triangle shape with a height-to-width ratio of one is ideal.
Interestingly, these ratios align closely with the traditional rooflines found in older buildings worldwide, including the ones Bejan observed in Italy. While he doubts ancient architects were consciously applying thermodynamics principles, Bejan believes their designs were not accidental.
Bejan emphasizes the importance of considering the physical shape of buildings in energy efficiency design. He suggests that modern architects could benefit from incorporating these principles into their designs to improve energy efficiency.
The study was supported by the U.S. Air Force Office of Scientific Research. Bejan hopes that this research will encourage architects and engineers to think creatively about the impact of physical shape on energy efficiency in building design.