Feature Stories

Growing Green On The Roof


On the Delmarva Peninsula, and across America, the green movement is focused on wind turbines and solar panels. But one Worcester County architect is hoping to add something else to the conversation: green roofs…or as they’re officially known: “vegetated roofs.” They typically consist of a 3-5 inch layer of special soil and hearty plants. They’re laid on top of the traditional waterproof membrane used in all roofs.

David Quillin has been an architect since 1997. He’s spent most of that time working out of his home office in South Point, a quiet community that overlooks Assateague Island and Assawoman Bay. Over the years, much of his focus has been on “sustainable designs,” homes and buildings that are environmentally friendly.

Buildings consume more than 50 percent of the overall energy we consume. David Quillin, Architect

He said if people really want to cut energy use, they need to pay more attention to buildings.

“Buildings consume more than 50 percent of the overall energy we consume,” he said. “Miles per gallon and vehicles get a lot of attention. But really the miles per gallon of buildings has a far greater impact on our energy use. Over 50 percent of all the energy we consume goes to building construction or building maintenance.”

That reduced energy use is why green roof technology has been embraced around the world. But this is not something new. It’s been around since the 1970’s. Europe is well ahead of America when it comes to vegetated roofs. Quillin says more than 10 percent of buildings in Germany now have them. But the trend is catching on in America, particularly in big cities.

Quillin has a a small patch of vegetated roof at his home. He uses it to show clients what it looks like and how it works.

He and several groups, like the Environmental Protection Agency and the International Green Roof Association tout the many benefits of a vegetated roof.


Reduced Energy Use: A green roof absorbs heat and acts as an insulator, reducing the need for heating and cooling.

“It does not exactly increase the insulation of the roof, but what it does is dampen the temperature swings that the roof insulation is exposed to,” Quillin said. “The house itself will stay cooler in summer and warmer in winter because there’s this 5 inches of thermal mass that kind of holds the temperature steady.”

Reduced Air and Water Pollution: Lower demand for air conditioning means less greenhouse gases from the AC units. But the roof gardens also pull pollutants out of the air.

This is not a new technology; this is done all over the world and has been for decades. David Quillin, Architect

“The atmosphere is filled with pollutants and on many days those pollutants gradually settle out onto everything…buildings, cars, and the ground,” Quillin said. “You wipe your finger on the car after a week with no rain, and that’s the grime. That’s a lot particulate pollutants that fall out of the atmosphere. Buildings get covered with all that, and then when it rains all of those pollutants get washed off the roof, and usually finds its way into the water pretty quickly.”

Those pollutants are typically nitrogen and phosphorous. Experts say those are the main culprits contributing to the poor health of the Chesapeake Bay and its tributaries. Quillin says a vegetated roof actually puts the bad stuff to good use.

“With a vegetated roof all particulates, nitrogen and phosphorous get settled onto the vegetated roof. When it rains those particulates get washed down into the root system of the vegetation. The vegetation uses them, it’s like fertilizer. So it basically converts these things that are pollutants into biomass, leaves and stems and benign things, So I think the biggest benefit is you short-circuit that cycle of pumping nitrogen and phosphorous into the waterways.”

Quillin also says vegetated roofs help to reduce flooding from storm water runoff. During the summer, they typically retain 75 percent of the rainwater that falls on them. In winter, it falls to around 40 percent.

Extended roof life

The typical roof lasts 15-20 years. When it’s replaced, all of the old shingles and materials get hauled to the landfill. Quillin says a vegetated roof, pitched or flat, lasts much longer.


Quillin’s Vegetative Roof

“What breaks down a flat roof normally are sun cycles and freeze/thaw cycles,” he said. “And a vegetated roof protects the membrane from both of those things. So a membrane that’s under a vegetated roof will last indefinitely.”

Quillin says green roofs improve the view, and ultimately people’s health, especially in cities. “They can be really beautiful, particularly for commercial buildings. It’s kind of hard to quantify the value of aesthetics, but there are a lot of studies that show workers call in sick 20 percent less if they work some place with views of vegetation and the outdoors. They get sick 30 percent less. You can quantify the value of a happier workforce that’s exposed to nature, vegetation in this way,” he says.

The Environmental Protection Agency estimates the cost of a green roof to be between $10-$25 per square foot, depending on the type of vegetated garden. There are two types: Extensive and Intensive. An intensive vegetated roof consists of 2 feet of soil, with hearty plants on top. Think of it as a giant planter on your roof. That extra soil adds significant weight, and cost. That’s why most green roofs are extensive, less than 6 inches of light soil and plants. Quillin says it’s important to make sure your roof can handle the extra weight.

Quillin says the soil mixture is very lightweight. It’s made mostly of vermiculite, a mineral that when processed becomes puffy and lightweight. Think small pieces of environmentally-friendly Styrofoam mixed with soil. The plants used are succulent plants and herbs that are hearty and drought-resistant.

The soil and plants are kept in trays that are 2 feet-by-4 feet. The trays interlock and are designed to allow the root system to spread from tray to tray. Quillin says once the trays are in place, there’s an initial watering phase to help everything get started. After that, there’s very little maintenance. Quillin says maybe a little weeding once a year, but even weeds have a hard time surviving in that environment.

The Worcester County architect says he’s designed four homes with vegetated roofs, but only one has been built. A Lewes homeowner says he’s very happy with how it turned out. A study by Green Roofs for Healthy Cities found that the number of vegetated roofs installed grew by 10 percent in 2013, and Washington, D.C. had the most growth.

They are more costly at first, but researchers say they pay off over the long run. The EPA cites a 2006 University of Michigan study. It compared the expected costs of conventional roofs with the cost of a 21,000-square-foot green roof and all its benefits, such as storm water management and improved public health from the absorption of nitrogen oxides. The green roof would cost $464,000 to install versus $335,000 for a conventional roof in 2006 dollars. However, over its lifetime, the green roof would save about $200,000. Nearly two-thirds of these savings would come from reduced energy needs for the building with the green roof. Granted a residential roof wouldn’t be that big, but the study offers a perspective on cost and benefits.

As David Quillin sits in his office working on a home design, he’s hoping to convince more home builders and homeowners to go green with a vegetated roof.

“This is not a new technology,” he said. “This is done all over the world and has been for decades. It’s a proven. It’s not a risky, exotic thing to do. It’s only new to this area. All the kinks have been worked out.”

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More Information

David Quillin, Architect, Berlin, MD

Environmental Protection Agency

International Green Roof Association

Green Roofs for Healthy Cities

Department of Energy Cool Roof Calculator

2006 University of Michigan Green Roof Study

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