Green Dream: Installing a Rooftop Garden

Rooftop greenery guards against water damage and bland meals

By John B. Carnett Posted 12.14.2009 at 2:08 pm Comments

The Green Dream: Vertical Garden John B. Carnett, PopSci’s staff photographer, is using the latest green technology to build his dream home. Follow his progress in each issue, and visit popsci.com/greendream for tips, videos of the build, and John’s blog. Peter Bollinger

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

The Specs

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

What's Inside: A Green Roof: Peter Bollinger

SOIL A four-inch bed of lightweight dirt is plenty to support herbs and wildflowers.
RUBBER Sheets of thermal polymer called TPO protect against temperature extremes and UV damage.
ROOF BOARD A fiberglass mat creates a hard, deck-like surface. It also thwarts mold and wayward roots.
ADHESIVE Sticky foam secures the roof board to the insulating panel below.
TAPERED INSULATION A layer of insulation installed at a slight pitch helps drain any excess water.
ROOF PANEL The garden’s foundation is an 11-inch-thick roof panel made of recycled expanded polystyrene that can support up to 70 pounds per square foot.

Already Have a Home?

Four Ways to Green Up Your Greenery

E-YARD GEAR Nearly 17 million gallons of gas are spilled annually refilling yard equipment. Ryobi’s new battery-powered chainsaw, string trimmer, leaf blower and hedge trimmer recharge in an hour, without a wasted drop of fuel. Plus, there’s no worrying about changing spark plugs. Available this month.
$100–$120; ryobitools.com
ECO-INSECTICIDE Based on plant oils that protect against insects, this natural insecticide from EcoSMART won’t harm people or pets. Spread the granules, which are infused with thyme, eugenol and sesame oil, over the lawn to kill more than 100 kinds of insects, including ants and mosquitoes. Available this spring.
$13/10-pound bag; ecosmart.com
A REEL MOWER
Gas-free mowers struggle through tall grass and twigs. The Fiskar Momentum uses a 6.9-inch-wide cutting wheel with 4.5-millimeter-thick blades to generate twice as much power as other reel mowers while requiring 30 percent less force to push. Lift the blades up to four inches with the touch of a button. Available this month.
$220; fiskars.com
SMART WATERING
Dial in specifics about your lawn’s environment, like soil type, climate and water requirements, and the Intelli-Sense irrigation controller calaculates an efficient watering schedule. The system uses daily updates from NOAA satellites and other weather data to trim your water use by up to 45 percent.
Starting at $325; toro.com

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

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finishing

12/22/12 at 2:02 pm

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.www.thaicartrick.com