Chances are, you don't spend a considerable amount of time on the roof of your home, and if you live in an apartment or home you probably don't even have access to it. But more communities are encouraging or even mandating this often invisible space to be a little more useful. In the City of Denver, citizens recently voted to pass Initiative 300, requiring all new buildings over 25,000 square feet to devote a portion of its roof to vegetation.
With an increasing focus on environmental and energy standards in the United States, developers are continually facing new challenges, and now they are expected to build green roofs. Although many might see this as local government overstepping an already highly regulated industry, the reality is that there are more pros than cons for developers to adopt green spaces into their planning, and roofs are no exception.
Natural Resource Management
When developing a property, you are not only concerned with the cost to construct but also the cost of maintenance throughout the life of the building. Stormwater management and energy costs are an increasingly regulated system in urban areas, and green roofs can reduce the price tag associated with both.
In many cities, developments often require a retention pond for stormwater runoff, requiring the purchase of additional land. With a green roof, such purchases can be reduced or mitigated entirely. For example, a 4″ extensive sedum roof could potentially capture 60-75% of annual rainfall. A deeper growing medium could retain even more water, reducing stress on sewage systems and instances of flooding.
Another benefit regarding natural resources is the thermal insulation and heat shield provided by green roofs. Studies have shown that the microclimate of an apartment underneath a green roof is comparable to that of one on the ground floor. In the summer months, HVAC systems can see a reduction in stress, leading to lower costs associated with maintaining air conditioning and coolants. Alternatively, in the winter, natural gas and oil costs are reduced as the green roof acts as an insulator, keeping heat inside the building. In fact, many green roofs have been known to reduce heat flux from roof to building by up to 72%.
Extended Life Expectancy
During their lifespan, roofs can take a real beating. With temperature fluctuation, UV-radiation, hail, and wind the average flat roof will only last 15-25 years. The cost to repair or replace a roof damaged by natural wear and tear can be mitigated by protecting it.
The waterproofing membrane and insulation of a traditional roof will see a reduction in physical and biological stress with the addition of vegetation. The life expectancy of a green roof can last 29-60 years. In Germany, there are many green roofs that have lasted over 50 years without a single leak.
Aesthetics and Increased Property Value
Developing new property is an investment, and no one wants to live, work, or shop in an ugly building. Ensuring that your property is aesthetically pleasing is not only important for attracting tenants, but also for increasing the value of your property over time. In many urban areas, vegetative roofs often replace the green spaces lost by the development of new residential and commercial buildings. Green roofs are also a more attractive and lucrative use of space. Since roofs are often severely underutilized square footage in a development, and by adding a green roof with vegetation or recreational space you can reduce the purchase of additional land at ground level.
Additionally, by adding vegetation to your roof you are adding a benefit to tenants and the surrounding community while bolstering the value of your property, making it more attractive to potential buyers in the future. Studies have shown that the addition of a rooftop garden increases occupant satisfaction, productivity, and psychological well-being. Green roofs also create a noise reduction barrier, which helps if you plan on developing near airports, entertainment districts, or industrial areas. By developing a building with a higher quality of life and lower energy costs, you could potentially justify a higher lease payment.
Cost-Benefit and ROI
Green roofs do have additional costs associated with the initial planning, building, and regular maintenance. But with all these benefits, are you saving money in the long run? The evidence we have so far states a resounding "YES." In a Cost-Benefit Analysis conducted by the U.S. General Service Administration, the return on investment for a green roof was at least 220% with a 5 1/2 to 7-year payoff. This is a national average, depending on the size of the roof and the complexity of the project.
The bottom line: green roofs are just as much of an investment as the building itself, creating value and putting money back into the pockets of developers and property managers. As is often the case with green initiatives, when done right there are just as many (if not more) economical benefits as there are environmental.