Green roof, Denver Botanic Gardens
Source: Denver Green Roof Initiative

Denver passed a green roof initiative this past November that took effect on January 1, 2018. I am hopeful that over time, it will improve Denver’s air quality, and I think it will be interesting to see it evolve. In today’s blog, I wanted to give you an overview of the new ordinance and some insight on how it’s expected to affect our market.

Denver’s New Green Roof Ordinance

Last November, voters in the City and County of Denver passed Initiative Ordinance 300, also known as the “Denver Green Roof Initiative,” by a margin of 54.3% to 45.7%.

The ordinance requires Denver buildings with 25,000 square feet or more of gross floor area to dedicate a percentage of the building’s roof area to green, vegetative space. The percentage that must be “green” increases as the building’s square footage increases, from 20% coverage for buildings between 25,000 and 49,999 square feet of gross floor area, up to 60% coverage for buildings with 200,000 square feet of gross floor area or more.

The ordinance applies to commercial buildings in Denver, as well as to residential buildings in Denver that are at least four stories high and have at least 25,000 square feet of gross floor area.

When Does It Take Effect?

Owners of buildings subject to the ordinance will need to make the change to a green roof at the time of a normal roof replacement. For a building built in 2017 (before the initiative’s passage), that could be 10-15 years from now. Developers of new buildings are subject to the initiative’s provisions right away. A building may have its entire roof covered in solar panels to be exempt, and other exemptions are available.

Benefits of Green Roofs

According to research conducted by the Environmental Protection Agency (EPA) in Region 8 (Colorado, Montana, North Dakota, South Dakota, Utah, Wyoming and 27 Tribal Nations), green roofs offer unique benefits:

• Green roofs create a place for stormwater to soak in, reducing the amount of stormwater runoff from a building. The foliage also slows and filters the stormwater that does run off the roof.
• Green roofs can reduce the Urban Heat Island Effect, in which large areas of concrete and the surface area of large buildings make the temperature about five degrees hotter in downtown than other parts of the city. (Denver is the city with the third-highest urban heat island effect in the United States, after Las Vegas, NV and Albuquerque, NM.)
• Having enough green roofs in a city can actually reduce the energy expenses of surrounding buildings as the urban temperatures are reduced
• Region 8 experiences very warm summers and very cold winters. Green roofs reduce energy expenses for buildings by providing insulation to reduce heat loss during the winter and air conditioned loss during the summer
• Due to our increased elevation from sea level, buildings in Region 8 are exposed to intense solar radiation, which damages the roof membrane. Green roofs extend roof lifespan by protecting the membrane from sun damage
• Green roofs can provide habitat for birds, butterflies, insects, etc.

Existing Green Roofs in Denver

The Denver Botanic Gardens (DBG) Green Roof, built in November 2007, is the first green roof on a city-owned building in Denver. In the 10 years since then, the DBG has kept meticulous records of the species they planted and the care they gave to the plants. As a result, they now possess unique insight into which plant species are well-suited to use on green roofs, as well as which are not (you can see their report here).

The EPA Region 8 building in downtown Denver has a green roof, covered in trays of sedums. The green roof provides insulation to the building, reducing heating and cooling costs. They have also done experiments with solar panels and the sedums. The vegetation keeps the solar panels cool and the solar panels provide shade for the plants.

Opposition to Green Roofs

The Denver Post published an editorial a few weeks before the November 2017 election, urging voters to vote no on the ordinance, stating that the cost of the improvements would be passed along to building tenants.

In a story on TheDenverChannel.com the week before the election, Andrew Friedson, an economics professor at University of Colorado Denver, said, “From an economic standpoint, it’s pretty well understood that whenever you put regulations on a building, it increases the cost of construction.” The professor didn’t go so far as to condemn the ordinance, saying, “I would argue if you’re going to do something like this, this is probably the better time, from a business-cycle standpoint in Denver, to do it.”

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