Why might a reflective top coating be applied to a BUR roof?

A reflective top coating is often applied to a Built-Up Roofing (BUR) system primarily to reduce cooling costs by reflecting sunlight. This is particularly important in warmer climates where the sun's heat can significantly raise the temperature of a building, leading to increased energy consumption for air conditioning. By reflecting sunlight, the top coating helps maintain lower surface temperatures, which can contribute to reduced indoor cooling requirements and overall energy savings.

This practice is part of a broader strategy known as "cool roofing," which aims to improve energy efficiency and reduce the urban heat island effect. The application of reflective coatings serves not only to enhance energy performance but also to extend the life of the roofing materials by protecting them from the degrading effects of UV radiation and heat exposure.

While other options mention repair, waterproofing, and structural integrity - these focus on different aspects of roofing maintenance and performance that do not directly relate to the primary purpose of a reflective coating. The main advantage lies in energy efficiency, which makes the correct reason for applying a reflective coating to a BUR roof centered around reducing cooling costs.