What is the primary material used to cover most commercial flat roofs?

The primary material used to cover most commercial flat roofs is tar and gravel. This roofing system is popular because it effectively provides a waterproof membrane that is crucial for flat roofs, where water drainage can be a significant concern. Tar and gravel roofs are constructed by applying layers of hot tar and embedding gravel on top, which not only helps in waterproofing but also adds weight to resist wind uplift and provides some fire resistance.

The use of tar and gravel is well-suited for commercial buildings, where durability and long-term performance are essential. This type of roofing can last for many years with proper maintenance, making it a cost-effective choice for many businesses. Its reflective properties can also help improve energy efficiency by reducing heat absorption.

In contrast, shingles and tile are more commonly associated with residential roofing applications, as they are typically designed for sloped surfaces. Metal sheets, while also used in some commercial roofing scenarios, are not the primary choice for flat roofs due to their cost and potential thermal expansion issues. Tar and gravel remains the standard due to its proven performance and suitability for the specific challenges presented by flat roof designs.