A Rooftop Garden with Altitude

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by Jane Anderson

I’ve always loved gardening. I grew up in a suburb of New York City, where I helped my family garden. So when my husband and I moved our family farther upstate, I looked forward to big, beautiful gardens on our 1-acre lot. What I got instead was an influx of destruction.

Every attempt at a vegetable garden turned into a feast for local wildlife. Chicken wire? The deer laughed at that. Wooden picket fencing? The chipmunks squeezed right through, and the groundhogs gnawed themselves an entryway. When I found a chipmunk running away from my damaged garden with a cherry tomato in its mouth, I’d had enough.

Our house is roughly barn-shaped, with a deep gambrel roof sloping down to the front and back. As a result, the tops of the house and the attached garage are flat. When our children were young, we set up a baby pool on the garage roof each summer; with southern exposure, the location was perfect. By 2018, they’d outgrown baby pools, and the roof deck laid dormant. I eyed my damaged garden attempts, and then eyed the deck. It was the perfect spot for a garden: constant sun and easy access through a sliding door, as well as gated stairs from our back deck. Before we could enjoy any bounty, however, we needed to do some research.

Our house was built with steel I-beams, rather than wood. During a home inspection, our inspector remarked that the roof deck’s structure could support an entire story if we’d ever want to build onto it.

Water, soil, drainage material, and plants weigh more than you think. Rooftop gardens can be “extensive,” such as potted plants or container gardens, or “intensive,” where the garden’s design is incorporated into the roof itself. While extensive gardens weigh about 20 to 34 pounds per square foot, intensive gardens range between 80 and 150 pounds per square foot, according to “A Guide to Rooftop Gardening” provided by the City of Chicago Department of Environment. That’s heavier than most roofs can withstand. So if you’re considering a roof garden, have a professional engineer or architect look over your site first.

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