The Building Owners and Managers Association — an organization for commercial real estate professionals — grades office buildings according to their competitive ability to attract similar types of tenants. A building's rating depends on a variety of factors including rent, finishes, system standards and efficiency, amenities, location, and market perception. 

1144 Fifteenth earns high marks for its amenities and modern design, image via Pickard Chilton

The grading system is broken down into three distinct categories. The 'Class A' designation is afforded to "prestigious" buildings which compete for "premier" office users. Rent at these properties is usually above the neighbourhood average. They typically feature high-quality finishes, state-of-the-art building systems, and easy accessibility. 'Class B' office space is characterized by average rents and finishes comparable to other buildings in the area. 'Class C' buildings compete for tenants "requiring functional space" at below-average rents. They are typically defined by older technologies and antiquated infrastructure. They may also be located in less desirable areas. A building's grade is relative to other properties in a given market. Therefore, a Class A building in a small town compared to Class A space in Manhattan will not share the same qualities. 

1000 Saint-Antoine West in Montreal, image retrieved from Google Street View

Dozens of office towers are under construction across the United States, including 1144 Fifteenth, Denver's first Class A office building in over three decades. It boasts a modern design, spacious floor plates, a mixed-use podium filled with amenities, and environmental features that earn it LEED Gold certification. On the other hand, the 1925-erected 1000 Saint-Antoine West in Montreal is a Class C property, likely losing marks for its age. 

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