Rooftop gardens are revitalizing cities and creating a beautiful oasis of greenery and color amidst concrete jungles. Urban gardens are lowering heating and cooling costs, providing ways to filter pollution from the air and to cut down on acid rain. There are two types of rooftop gardens: extensive gardens, which weigh less and uses a combination of a thin layer of soil and containers, and intensive gardens, where layers of protective membranes are installed and soil is brought into to create landscaped gardens.
Extensive Rooftop Gardening
Sketch a basic layout of the garden. Include the size of the roof. Consult an architect or structural engineer to find out how much weight the roof of your building can handle. Acquire a building permit because most but not all cities consider rooftop gardening construction. Purchase these items for extensive gardens: waterproofing membrane (available as a vinyl coating that can be painted), roof membrane (polymer-modified bitumen sheets) to protect the roof from root damage, irrigation system (rain barrels and a garden hose), drainage system (layer of pea gravel and filter fabric), containers for growing, soil and vegetation.
Coat the rooftop with waterproofing membrane and allow to dry. Depending on the ambient temperature and humidity, this will take one to two days. Install bitumen sheets as the roof membrane. Cover the roof membrane with 2 inches of pea gravel and a filter fabric (woven geosynthetic fabric) to create the drainage system.
Layer soil to a depth of 5 inches. Put rain barrels in easily accessible locations. Connect a garden hose to an outdoor spigot. Place growing containers in their designated spots and fill with soil. Plant desired vegetation. Set up a barrel compost bin.
Intensive Rooftop Gardening
Paint the rooftop with vinyl coating to protect it from water damage. Place a layer of protective board (quarter-inch polyurethane) to protect from damage from construction. Install foam board insulation across the roof. Layer bitumen sheets over the insulation.
Install a drainage layer with pea gravel and cover with filter fabric. Cover with one foot of soil. Install an irrigation system using rain barrels and hoses connected to an outdoor water spigot. Drip irrigation using hoses or PVC pipe can be installed in intensive rooftop gardens.
Plant desired vegetation and install a barrel compost bin. Lay down a burlap blanket over exposed soil to prevent soil blowing away until vegetation has had time to take root. Cut small burlap blankets to place around trees and other large plants to hold mulch in place.