How To Design a Roof Garden

If you live in an urban area, you may think that having a garden is a goal that will never be realized.  If so, you're just not thinking high enough!  More and more communities are encouraging their residents to plant roof gardens, or green roofs, as they're sometimes called.  The psychological and environmental benefits of roof gardens are numerous.  Gardening can be calming and relaxing, which in turn decreases the incidence of stress-related illnesses.  It's also beneficial to the environment, particularly in urban areas.  Adding a green roof to your house or apartment building can decrease storm water runoff, reduce fire risks, help decrease heating and cooling costs, and control pollutants from rain water.  In addition, a roof garden can improve the aesthetic quality of a building.  In fact, many communities now have ordinances which require a certain percentage of new construction to have green roofs.

1. The first consideration when installing a roof garden is the roof itself.  Your roof must be reasonably flat and have some kind of access.  After all, you can't enjoy your garden if you have to climb a ladder every time you want to look at it.  It must also be capable of supporting a heavier-than-normal load.  Wet soil can weigh more than eighty pounds per square foot.  If your roof can't support this much weight, you can still have a roof garden, but you'll have to settle for gardening only in containers, or structurally altering your home. 

2. If your roof passes these first three criteria, next you'll need to be sure it has a waterproof membrane.  Otherwise, you could end up with a very wet ceiling in your home!  Two of the most commonly-used waterproofing materials are thermoplastic sheeting and rubberized asphalt.  Keep in mind that you will want an extremely durable membrane, so that you don't have to dig up your entire garden to replace it in a few years.
3. Once you've determined that your roof is capable of sustaining a garden, you'll need to consider your climate.  If you're in an urban area with many tall buildings, your building may be partially or mostly shaded for a good part of the day.  You'll need to consider this when choosing plants.  If your roof is in direct sunlight for much of the day, it may be much hotter up there than on the ground.  This can also be very drying for the plants that you choose, as can the higher winds that are prevalent among rooftop gardens.  Many plants that are drought-tolerant will do well when planted on roofs.
4. Now that you know what kind of plants you need to plant, think about what kind of garden you'd like to have.  The possibilities are limited only by your imagination.  Any kind of garden that can be planted on the ground can usually be a roof garden, just reduced in size.  Container gardens can be particularly appropriate.  If you need some ideas, purchase a book on small-space gardens.  Most of these can be planted on roofs, also.  There are also many books which deal specifically with green roofs.
5. When planting your roof garden, you'll need to pay special attention to the materials that you use.  Plastic pots are lighter than clay or terra cotta.  If you want to use large rocks in your garden landscape, you'll need to use those which are made of a fiberglass composite, rather than the real thing.  In general, try to use lightweight materials to reduce the strain on your roof.

Now that you've designed your perfect rooftop garden, get busy planting and have fun!