Home Grown: A Green Roofs Primer

Enlarge Image Image Gallery Green roofs, such as these in Norway, have been common in Scandinavia for centuries.

When Diana Cohen and her husband, Wes Slaymaker, decided they needed more space in their home in Madison, Wisconsin, they looked up rather than out. Hoping to enlarge their living area without increasing their ecological footprint, they decided to build an “addition” on top of their house by installing a green roof. After consulting a structural engineer, they resolved to build the 220-square-foot structure themselves. Several months of research, a few weekends of installation and $1,500 later, the Cohen-Slaymakers have a luscious outdoor living space where they can relax, grow food and watch birds, bees and butterflies at work. 

You, too, could increase your family’s living and gardening space by installing a green roof. Although modern green roofs are a fairly new concept, the idea of rooftop gardens is ancient. The hanging gardens of Babylon, a series of terrace gardens that are one of the Seven Wonders of the World, were constructed in 600 B.C. in what is now Iraq. Sod houses dotted the American prairie during frontier settlement, and green roofs have been scattered across Scandinavia for centuries.

Modern green roofs—composed of vegetation and layers of growing medium such as shale and compost—were introduced in Germany in the late 1950s. They have since exploded in popularity throughout Europe and are on the rise in North America. Though green roofs are more common on commercial buildings, homeowners are also taking advantage of this living home improvement.

Raise the roof 

There are plenty of reasons to get excited about a green roof. They can offer expanded outdoor space without requiring more land. They provide a fabulous place to grow food and host parties. And they attract birds and beneficial insects to your home.

Green roofs also help manage rainwater, diverting 50 to 90 percent of rooftop precipitation from the sewer system and returning it to the water cycle. Excess stormwater drains more gradually, reducing the sewer system’s peak flow volume. Green roofs aid efficiency by moderating temperature extremes. By providing modest thermal insulation, green roofs keep homes cooler in summer and a bit warmer in winter. High volumes of concrete and buildings create “heat islands” in many cities. Through heat absorption, green roofs help lower urban temperatures. Most roofs are exposed to ultraviolet rays, temperature extremes, hail and other elements. Green roofs buffer those elements and can double the lifespan of rooftop waterproofing.

For urban homeowners without yards, green roofs offer the opportunity to garden. “We’re seeing a lot of people moving toward rooftop agriculture, especially in areas where land space is difficult to come by,” says Ty Voyles, Green Roof Professional for DC Greenworks. “To use it to grow produce is a really inventive and ingenious way of using that space,” he says.

Root structure