City Engineering encourages the use of green roofs on city facilities. Five city buildings have green roofs including the Madison Municipal Building, Central Library, Fire Station 12, Water Utility Operations Building, and the Larry D. Nelson Engineering Operations Building.
A green roof or living roof is a roof of a building that is partially or completely covered by vegetation. A green roof consists of the vegetation, growing medium (soil), tray system, root barrier, drainage layer, and protection layer. A green roof must be maintained with occasional weeding and watering practices.
There are two different types of green roofs – an extensive green roof and an intensive green roof. An extensive green roof system is six inches or less in height and weighs 15-50 pounds per square foot. The extensive system is generally lower maintenance and more common than the intensive system. An intensive green roof system is over 50 pounds per square foot and supports a larger variety of plant species due to the deeper soil medium.
The Facilities Section encourages the use of green roofs due to the numerous benefits. Some of the benefits include:
- Stormwater Management: Reduces the volume and peak runoff rates of stormwater leaving a site by absorbing water.
- Thermal: Prevents the roof from becoming hot in the summer and transferring that heat to the inside of the building which would require additional cooling. Green roofs do not provide direct thermal resistance like insulation.
- Economic: Protects the roof membrane from sun and ultraviolet degradation which extends the life of the roof membrane.
- Aesthetic: Provides pleasant roof view compared to an exposed membrane roof.
- Habitat: Attracts pollinators like bugs, bees, butterflies and birds.
- Green Building Certification: Using a green roof provides points for green building certification.