Rooftop Gardens in Urban Spaces

If you don’t have a lawn but want a garden, consider putting one on your roof! If properly created and maintained, you’ll have the benefits of a healthy garden while saving space.

Rooftop gardener

Steeply slanted roofs make it hard — although not impossible — to garden on.

Photo by Fotolia/kazoka303030

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Abigail Gehring has put together a simple and informative guide to basic independent living in Self-Sufficiency. Whether families are trying to move completely off the grid or just reduce their impact on the environment, this book is full of tips, advice, and instructions for everything, from tasks like building furniture and water systems to raising animals and making soap. Use this resource to find inspiration on living greener and more responsibility.

If you live in an urban area and don’t have a lawn, that does not mean that you cannot have a garden. Whether you live in an apartment building or you’re a homeowner without yard space, you can grow your very own garden, right on your roof!

Is Your Roof Suitable for a Rooftop Garden?

Theoretically, any roof surface can be greened — even sloped or curved roofs can support a layer of sod or wildflowers. However, if the angle of your roof is over 30 degrees you should consult with a specialist. Very slanted roofs make it difficult to keep the soil in place until the plants’ roots take hold. Certainly, a flat roof, approximating level ground conditions, is the easiest on which to grow a garden, though a slight slant can be helpful in allowing drainage.

Also consider how much weight your roof can bear. A simple, lightweight rooftop garden will weigh between 13 and 30 pounds per square foot. Add to this your own weight — or that of anyone who will be tending or enjoying the garden — gardening tools, and, if you live in a colder climate, the additional weight of snow in the winter.

Will a Rooftop Garden Cause Water Leakage or Other Damage?

No. In fact, planting beds or surfaces are often used to protect and insulate roofs. However, you should take some precautions to protect your roof:

1. Cover your roof with a layer of waterproof material, such as a heavy-duty pond liner. You may want to place an old rug on top of the waterproof material to help it stay in place and to give additional support to the materials on top.

2. Place a protective drainage layer on top of the waterproof material. Otherwise, shovels, shoe heels, or dropped tools could puncture the roof. Use a coarse material such as gravel, pumice, or expanded shale.

3. Place a filter layer on top of the drainage layer to keep soil in place so that it won’t clog up your drainage. A lightweight polyester geotextile (an inexpensive, non-woven fabric found at most home improvement stores) is ideal for this. Note that if your roof has an angle greater than 10 degrees, only install the filter layer around the edges of the roof as it can increase slippage.

4. Using moveable planters or containers, modular walkways and surfacing treatment, and compartmentalized planting beds will make it easier to fix leaks should they appear.

How to Make a Rooftop Garden

Preparation

1. Before you begin, find out if it is possible and legal to create a garden on your roof. You don’t want to spend lots of time and money preparing for a garden and then find out that it is prohibited.

2. Make sure that the roof is able to hold the weight of a rooftop garden. If so, figure out how much weight it can hold. Remember this when making the garden and use lighter containers and soil as needed.

Setting Up the Garden

1. Install your waterproof, protective drainage, and filter layers, as described above. If your roof is angled, you may want to place a wooden frame around the edges of the roof to keep the layers from sliding off. Be sure to use rot-resistant wood and cut outlets into the frame to allow excess water to drain away. Layer pebbles around the outlets to aid drainage and to keep vegetation from clogging them.

2. Add soil to your garden. It should be 1 to 4 inches thick and will be best if it’s a mix of three-fourths inorganic soil (crushed brick or a similar granular material) and one-fourth organic compost.

Planting and Maintaining the Garden

1. Start planting. You can plant seeds or seedlings, or transplant mature plants. Choose plants that are wind-resistant and won’t need a great deal of maintenance. Sedums make excellent rooftop plants as they require very little attention once planted, are hardy, and are attractive throughout most of the year. Most vegetables can be grown in-season on rooftops, though the wind will make taller vegetables (like corn or beans) difficult to grow. If your roof is slanted, plant drought-resistant plant varieties near the peak, as they’ll get less water.

2. Water your garden immediately after planting, and then regularly throughout the growing season, unless rain does the work for you.

Things to Consider

1. If you live in a very hot area, you may want to build small wooden platforms to elevate your plants above the hot rooftop. This will help increase the ventilation around the plants.

2. When determining whether or not your roof is strong enough to support a garden, remember that large pots full of water and soil will be very heavy, and if the roof is not strong enough, your garden could cause structural damage.

3. You can use pots or other containers on your rooftop rather than making a full garden bed. You should still first find out how much weight your roof can hold and choose lightweight containers.

4. Consider adding a fence or railing around your roof, especially if children will be helping in the garden.


Benefits of Rooftop Gardening

• Create more outdoor green space within your urban environment.
• Grow your own fresh vegetables — even in the city.
• Improve air quality and reduce CO2 emissions.
• Help delay storm water runoff.
• Give additional insulation to building roofs.
• Reduce noise.


For more from this book, see: A Comprehensive Guide to Beekeeping Basics.


Reprinted with permission from Self-Sufficiency: A Complete Guide to Baking, Carpentry, Crafts, Organic Gardening, Preserving Your Harvest, Raising Animals, and More by Abigail R. Gehring, published by Skyhorse Publishing, 2010.