To qualify for an area factor increase based on frontage, a building must have a minimum of what percentage of its perimeter on a public way or open space?

To qualify for an area factor increase based on frontage, a building must have at least 25% of its perimeter adjacent to a public way or open space. This requirement is often established in zoning ordinances to ensure that buildings are sufficiently integrated into the urban fabric and have accessibility, visibility, and a presence in relation to public spaces.

Having a significant portion of a building's perimeter facing a public way or open space contributes to the overall planning and development goals of ensuring that buildings not only benefit from public exposure but also enhance the urban environment by encouraging interaction between the building, pedestrians, and surrounding infrastructure. This threshold is set to strike a balance between site utilization and making sure that developments contribute positively to the public realm.

Lower percentages, like those suggested in the other options, would not fulfill the intent of promoting buildings that engage adequately with their surroundings and could consequently undermine the public interest in urban design and accessibility standards. Thus, 25% is the minimum required to qualify for this increase, reflecting a commitment to effective urban integration.