Rooftop gardens not only improve the aesthetics of your home, but also function as insulation, protecting your house from sudden temperature fluctuations. Intensive rooftop gardens house large shrubs and trees requiring 4 to 6 feet of soil and the ability to support 150 pounds per square foot. These gardens are usually flat and open to people, and specifically called "roof gardens." Extensive rooftop gardens, on the other hand, require little maintenance and exist for environmental purposes. These are called "green roofs" and are not open for traffic.
Find out whether your roof and home can withstand the pressure of a roof garden. For this, you may have to enlist the help of a structural engineer. For an intensive roof garden, it has to be able to support 80 to 150 pounds per square foot and be relatively flat. You may have to make changes to your roof to make it accessible and sound.
Apply for a permit at your local zoning or building department. Before construction begins, you will need to prove that your building can withstand this design. You will need to supply drawings of existing roof conditions, structural framework, weight capacity (including snow load) and the proposed garden.
Remove the existing roofing on your home. Apply a waterproof membrane to protect your house from moisture. Look for one that is resistant to decay from the acids that plants emit. The best type of waterproofing material is called a monolithic membrane, which is a rubberized asphalt applied as a hot liquid.
Add a chemical or physical root barrier. This will protect the roots of your garden from piercing the waterproof membrane. A drainage layer made of clay, plastic or gravel goes on top of that, taking care of excess water and maintaining airflow. Next comes a geosynthetic filter mat, which prevents fine particles from washing away.
Add a lightweight growing medium ontop of the protective layers. For rooftop gardens, this usually consists of high quality compost and recycled materials. These materials will retain water and air and resist rot, heat, flying sparks and frost. Apply as much medium as your plants will need to grow effectively.
Plant the shrubs, trees and other plants you wish to grow on your roof. Maintain these plants properly, watering, fertilizing and pruning to keep them healthy and in check.