What’s a green home without actual greenery? I wanted my eco-friendly house to feel more connected to nature, so I turned the flat stretches of roof into gardens. Rooftop flora is not only scenic, but it can also protect a home against temperature extremes, absorb carbon dioxide, and triple the life span of a roof.
The first thing to know about building a green oasis on top of your home is that dirt is heavy, and it gets even heavier when wet. Before I did anything, I consulted an engineer to figure out the maximum load my roof could handle. Standard green roofs hold four inches of soil and weigh 15 to 20 pounds per square foot. The deeper the soil, the more options for planting, but four inches is plenty of depth to grow a wide range of flowers and herbs.The next step was prepping the roof for proper drainage and waterproofing. First I put down a tapered layer of insulation to channel excess water into storage tanks on the ground. Over that goes a layer of deck paneling secured to the roof with foam adhesive. These panels provide a hard surface for the garden and keep wayward roots from reaching the roof. The final layer is a special weatherproofing rubber.
With the roof fully protected, I was ready to add soil. Some people toss dirt over the entire roof, but I opted to load it into a patchwork of trays. Containers are easier to install and easier to remove should the roof require repairs. Many companies deliver trays fully loaded with lightweight soil specially designed for green roofs and mature plants. Although these are convenient, some cost up to $20 per square foot. By buying the trays and soil in bulk and loading up the trays myself, I was able to reduce the cost to about $5.50 per square foot.
The fun part—actually planting things—starts this spring. Look for all the details on that in the March issue.
Next month: Save copper with wireless light switches
House: 3,500-square-foot, four-bedroom contemporary
Location: Greenwich, N.Y.
Project: Building a green roof
Cost of materials: $15.50 per square foot for entire project
Time to install: Six days
Eco-advantage: Creates wildlife habitats, absorbs CO2, insulates roof
John B. Carnett, PopSci's staff photographer, is using the latest green technology to build his dream home. Follow along as the project progresses on his Green Dream blog: popsci.com/green-dream
Five amazing, clean technologies that will set us free, in this month's energy-focused issue. Also: how to build a better bomb detector, the robotic toys that are raising your children, a human catapult, the world's smallest arcade, and much more.