The green roof on the Chicago City Hall, with a growing medium that varies from 3 to 24 inches in depth and includes a variety of plants such as grasses, succulents, and trees, is best described as intensive and extensive.
- Extensive green roofs typically have a growing medium depth of up to 6 inches and are generally planted with drought-resistant plants like sedums and mosses.
- Intensive green roofs have a greater depth of growing medium (usually over 6 inches) and can support a wider variety of plants, including shrubs and small trees.
Given that the depth ranges from 3 to 24 inches, it supports the presence of more diverse plant life, which indicates characteristics of both intensive and extensive green roofs.
Therefore, the correct response is intensive and extensive.