|The same general principles described in Urban Gardens and Farming can
be applied to rooftop gardening.
roof plantings may provide food, temperature control, water-saving benefits, architectural enhancement, habitats or corridors for wildlife, recreational opportunities, and in large scale it may even have ecological benefits.Discovering the load-bearing capacity of a purpose-built roof garden is easy – you simply need to look at the title deeds. When it comes to older properties, chances are the space was originally intended to be somewhere to hang out the washing, or access the roof. How much weight it can take is debatable, and it’s likely you won’t find the information on the title deeds.
I'm going to discuss rooftop gardens on smaller, one and two story buildings, not tall apartment buildings. That takes a lot more consideration than putting one onto a one family home.
In order to be certain, consult a structural engineer who will calculate what you can – but more importantly what you can’t do – on an older-style roof garden.
New roof gardens are often seen to be an extra floor, and if you live in a conservation or urban area, you’ll need to check any plans with the local authority. Get a permit. Get it inspected for safety after it's complete.
Access and safety of your rooftop garden
Access is another key factor that will affect what you can do with a rooftop space. You’ll probably need to bring materials and plants up and down and perhaps through the house, so always measure stairwells, corridors and doorways to check that you can easily maneuver plants and materials.
Safety is of course paramount, so avoid hanging anything over the edge or placing pots on ledges, unless they’re firmly secured. Do check with your local authority though – some won’t allow you to do this. Pergolas, trellis, wirework or shade sails should be fixed securely, with the fixings easily accessible so that they can be tightened regularly. The balcony needs to be in good condition too
If weight is an issue, there are obvious things you can do. Plastic planters, along with fibreglass imitations, weigh much less than concrete, stone or terracotta containers. Avoid placing pots in the centre of a roof terrace and don’t have too many (fewer containers look better). Fixing pots to surrounding walls or placing them on cantilevered shelves will help as the walls will be taking the weight, not the roof. Also, choose lightweight collapsible garden furniture instead of a huge, glass-topped table.
Factor in wind when designing a rooftop garden
Wind is a common problem in rooftop gardens. Many plants can cope with it, but you might need some shelter if you want to enjoy the space all year.
Taller wind-tolerant shrubs offer some protection. Think of them as a living screen.
Go for a simple, linear layout with contemporary materials such as polished stone, rendered walls, Cor-Ten steel or concrete, or traditional ones such as woven hazel and clay pavers using them in a modern way. Choose materials to complement patterns or colours in the surrounding landscape or adjacent buildings so the design blends in.
Whatever layout you choose, take account of the view.
Outdoor lighting can be a very effective addition to a rooftop garden design scheme. Plan your lighting with the specifics of the rooftop location in mind, avoiding designs that are lightweight and flimsy, as they will most certainly be ripped off by strong winds. I like the pathlight types that can be stuck firmly into the ground, or hung on any fencing you might have installed.
Be aware of how your rooftop garden lights affect your neighbors. I have some issues with a neighbor's spotlight across the alley, shining like a beacon into my kitchen at night, if he forgets to turn it off. It's in his backyard, and his backyard faces my backyard. You don't want to interfere with traffic, either. Youdon't need high-powered lights up there. You won't be gardening at night. It's best to use solar path lights, ssmall tring lights or dimmable lights to create a relaxing ambience if you'll be relaxing or enjoying cocktails up there. Bright lights on a roof remind me of the movies about prisoner escapes. Duck and run. Doesn't sound very relaxing to me. And you'll attract bugs. I like using the mason jar fairy light strings - the jars can be hung wherever you like or set upon a bistro table.
Consider built-in wall lights if you have access to electricity, if you still want the dreamy ambience of fairy lights, choose ones that are on the heavier side, and position them in a sheltered corner above seating, or attach them to a wall.
Fencing - anything other than decorative garden edging, or fencing that you install so that you are safely traversing your roof, should be approved by your local inspector/permitting agency. As if you were building a balcony. Structure is important. And fencing needs to be stable and firmly grounded. You don't want to install anything that might fly off in a storm and hurt someone, damage someone's property, or cause traffic accidents. Just look at the design as everything having to be permanently rooted to the roof or the planters.
Be aware of how you place the container plants. They will be heavy, filled with soil. Consider putting large planters with shrubs and trees on those plant lifters. But skip the wheels. Last thing you want is for your large, heavy containers and landscapes rolling off the roof.