France is leading the “cool roof” movement. All new buildings in commercial zones across the country must comply with new environmental legislation-they must be covered in plants or solar panels.
Cool roofs are one of the leading green building technologies used today, and while it is not a new concept, cool roofs are working to solve a growing problem. Think about how you’d dress on a hot August day. Do you wear all black? Generally not. You wear light, airy, heat reflective colors like white or blue or yellow. So why do we choose to disregard what builders in hot climates have been doing for hundreds of years, and cover our roofs with dark, non-reflective, heat-absorbing materials?
In densely populated areas like cities and suburbs, these choices have real-time consequences. These cities have been dubbed “heat islands” because of the huge variance in temperature caused by the built environment.
Chris Briley, Principal at BRIBURN, a reputed New England architecture firm dedicated to sustainable design, explains, “In the south, the heat island effect is very real. The city can be 5-10 degrees hotter than the surrounding suburbs and that’s because of dark pavement, dark roofs and a lack of respiring vegetation.” Something as simple and inexpensive as choosing a light color roof paint instead of black shingle or tar can immediately normalize surrounding air temperatures and help bring down the “heat island” effect.
Are cool roofs worth considering up north?
While New England’s cooler climate might not make “heat islands” a top concern, a creative twist on cool roofs help to solve a different problem here. Water quality. Enter the beautiful and functional “vegetated roof.”
A vegetated roof remembers technology that people have been using for centuries. By covering the roofs of both homes and office buildings with plants, we can greatly improve storm water conditions. The roof can absorb and hold the water of a 1” rainstorm, and any water that then runs off the roof and into streams, lakes, ponds and eventually the ocean has been preconditioned with sulphurs and phosphates and already neutralized.
“Imagine districts like Portland, Maine,” Briley positions, “with a direct watershed to Casco Bay and a combined sewer system. Every large storm is bad for Casco Bay because of the overflow and unconditioned runoff from our urban and suburban districts. If every roof were a vegetated roof, this negative effect would be greatly reduced.”
Plus, vegetated roofs are cool roofs in the traditional sense that when temperatures are hot, they cool the structure down. Briley explains that because as the plants respire, their heat gain in the summer is ZERO. That can have a huge effect on the cooling load and energy use of an air-conditioned building, as well as increase the comfort of a non air-conditioned building or home. The expense of air conditioning doesn’t make it worth it to most New Englanders, but there are summer months when all of us would appreciate a cooler interior temperature. Vegetated roofs provide that.
“This may seem like a small thing, but you are covering your roof with a natural material that will sequester carbon and release oxygen. And of course, they look beautiful.” – Chris Briley, Principal, BRIBURN
For all of the reasons outlined here, TideSmart Global, a marketing firm based in Falmouth, Maine, is working with BRIBURN on the design and installation of 5,000 ft2 of vegetated roof at their logistics center. The hope is that such a high profile and large-scale cool roof will likely bring attention to the vegetated roof as a viable New England construction feature.
Is a cool or vegetated roof right for you?
There are many more benefits to installing a cool roof at your home or office. Decreased utility bills, increased occupant comfort, extended roof life and even utility rebates in some locations are helping homeowners decide to make the switch. Because of New England’s cooler climate, vegetated roofs are becoming more popular, but there are many factors to take into consideration before deciding on the best cool roof material for you.
What about the snow loads we see here in the New England? A leaky roof is independent of whether it’s green roof or traditional. It has to do with the installation and design specification of the structure. All roofs must have a proper waterproofing membrane, green roofs included.
There is no evidence to suggest that green roofs are more susceptible to leaking. In fact, some studies suggest that the longer life cycle of a green roof is due to the protection of the waterproof membrane from ultraviolet sunlight. The plants and substrate act as a natural barrier to weathering.
The Cool Roof Rating Council offers a multitude of resources to help guide you through building material options, rebate opportunities, and even reputable contractors.