Green Building Community
Denver to require rooftop gardens to reduce heat island effect
Posted by: Kalyani.rc // Passive House / Sustainability Enthusiast
Denver’s status as one of the nation’s most intense urban heat islands has spurred a group of activists to propose a “green roofs” ballot initiative — a measure that could animate environmentalists while mobilizing developers to fight it.
How green roofs can help:
In large cities, heat-radiating roofs and pavement often elevate temperatures several degrees in the summer heat. A 2014 analysis by Climate Central, a scientific advocacy group, found that semi-arid Denver’s average daily summertime temperature during the previous 10 years was 4.9 degrees higher than in nearby rural areas; it recorded the third-largest “heat island” effect among U.S. cities, behind Las Vegas and Albuquerque.
Advocates of green roofs — also called “living roofs” — say the increased vegetation reduces that heat effect, results in less storm-water runoff and also helps fight air pollution.
What the initiative says:
The proposal sizes up a new building based on gross floor area (excluding parking) and sets an increasing percentage of available roof space that must be covered by “green roof” components.
The required coverage proportion ranges from 20 percent for buildings between 25,000 and 50,000 square feet to 60 percent for buildings of more than 200,000 square feet.
Industrial buildings would face different requirements, while multifamily residential buildings of four stories or less would be exempt entirely. Building owners also could opt to incorporate solar panels to fulfill part of the requirement. City officials would be able to make other exceptions or allow smaller roof gardens in certain cases.
The green roof requirements also would be triggered for existing large buildings by roof replacements and additions that increase the size to 25,000 square feet or larger.
Other American cities, including Chicago, Seattle, and Portland, have tended to offer density bonuses or other incentives to encourage the incorporation of green roofs, rather than blanket requirements. Denver offers no building incentives for green roofs.
Denver updated its building code last year. The Department of Community Planning and Development was hesitant to pursue a green roof mandate.
Spokeswoman Andrea Burns said the department would prefer to give architects and engineers “the flexibility to design a roofing system that works best for their needs and their budgets” — while leaving it to builders to decide whether to incorporate green or solar components.
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