What is the primary purpose of gravel on a built-up tar and gravel roof?

The primary purpose of gravel on a built-up tar and gravel roof is to provide ballast to help secure the roofing membrane. The weight of the gravel is crucial in keeping the roofing system in place, particularly in areas prone to high winds. This stability is essential, as it prevents the membrane from lifting or becoming dislodged, which can lead to leaks and other structural issues. Additionally, the gravel layer helps to protect the underlying membrane from ultraviolet (UV) degradation and physical damage, thereby extending the life of the roof.

While insulation, aesthetic appeal, and water drainage efficiency are important factors in roof design, they are not the primary functions of gravel in this specific roofing system. Insulation is typically provided by other materials, aesthetic considerations can vary widely based on design preferences, and water drainage is generally managed through the roof's slope and drainage system rather than through the gravel itself. Thus, the critical function of gravel as ballast is what defines its essential role in maintaining the integrity and longevity of a built-up roof.