If you’ve read any of our articles, you know that there are a lot of benefits to installing a green roof. Any discussion around whether or not to incorporate a green roof will ultimately come to one thing: “How much does it cost?”
In many cities, Denver included, it may cost you more, or just as much to NOT install a green roof. The city of Denver Green Roof Ordinance requires that any building project over 25,000 square feet have at least 20% of it’s roof space be vegetative. You can view the specific requirements here.
Of course there are exemptions, as well as a $25/square foot cash in lieu fee if a developer decides not to install a green roof in accordance to the ordinance. But the application process is lengthy and expensive, and many extensive green roof systems that fall under the cities guidelines can cost much less than $25 a square foot(1).
Let’s use the new construction of a 300,000 square foot office building with a roof size of 6,000 square feet as an example. If Denver requires that 60% of the roof be green, then 3,600 square feet of the roof will need to be vegetative. The cash in lieu price is $25/square feet, so if you decided to not install a green roof, you will already be paying at least $90,000. That doesn’t include the $4,000 - $20,000 you might have to pay structural engineers or consultants to show proof that your planned or existing structure cannot support a green roof (2). If you ignore the mandate entirely, you could be fined up to $999 per year and imprisoned for each day you do not comply with the law (3).
Obviously this example is one of many scenarios, and it may not make sense for certain development projects to have a green roof. However, there is a Green Roof Task Force Committee determining how to make options for developers to install environmentally friendly roofs at an affordable price. It is also important to note that developers will need to have Green Roof permits for new construction, and roof replacement permit for existing structures.
In many cities the impact of a conventional roof and the resulting urban heat island effect is not compensated for after a building is constructed. With Denver being the 3rd highest urban island effect city in the U.S., it makes sense that everyone do their part to help mitigate the environmental impact of large development projects.
With the kind of price tag the cash in lieu fees alone will cost, you could easily build a green roof for less or close to that amount of money. And even if the costs of installing a green roof exceeded the cost of the cash in lieu price, the heating and cooling reduction alone would compensate for the difference. Green roofs also come with some nice perks such as higher valuation, reduced costs in storm water fees, and additional amenity space. Green roofs just make good financial sense.