Last Updated on
If you learn how to build a rooftop garden, you will not only make your otherwise dull rooftop a beautiful spot but also be able to grow all seasonal flowers, almost all perennial flowers, almost all vegetables and fruits and all succulents.
All over the world, rooftops of keen urban gardeners and environmentally aware people have been transformed into living green areas which have numerous benefits including growing your own flowers and vegetables.
Wouldn’t it be great to have a few home-grown vegetables for dinner or a bunch fresh-cut roof flowers for your living room vase?
Plants take carbon dioxide out of the air while releasing breathable oxygen. If you live in an apartment or a house with no yard, rooftop gardens can still let you do a world of good for the environment while growing ornamental trees and bushes, flowers, and edible plants.
Contact a structural engineer and map out your garden before you begin planting. Choose the right plants and decorations to make the most of what space you have.
If you enjoy gardening but find yourself limited by space, rooftop gardening can provide an excellent alternative, especially for city dwellers. These gardens have numerous benefits as well. You can make use of space that would otherwise go unused and turn a gray rooftop into a beautiful and peaceful spot.
Types of rooftop gardens
Rooftop gardens not only provide a unique way for city gardeners to do what they love most. In addition, depending on the type of garden you go for, you can also save on energy since rooftop plants supply buildings with additional insulation and shade.
There are three types of rooftop gardens. They vary in terms of construction and purpose.
Firstly, you can make a container garden on your roof and grow smaller plants, herbs flowers, and vegetables.
Secondly, you can install a lot of raised beds to grow different plants in greater numbers. These raised beds can be either permanent (made of concrete) or wooden, plastic or metal.
Lastly, you can make your whole roof or a selected part a vegetation ground like a regular garden. This will require much more planning, efforts and time but your green roof will have greater benefits on a larger scale.
What about drainage and insulation?
Every rooftop garden consists of several layers which serve specific purposes and are made of appropriate materials. Here’s one example of the rooftop garden layers:
1. Waterproofing Layer
Your roof must be waterproof, durable and frost resistant. If you decide to start growing plants on it, the roof must be waterproofed. This goes for growing plants in containers, raised beds or on the roof itself and should be the first step in order to protect the roof from leaking.
Waterproofing should cover up the whole surface of the roof and spots where the plants will be planted need special attention.
2. Insulation Layer
The insulation layer (Protection Layer) makes a roof garden resistant to moisture and temperature fluctuation and provides sufficient mechanical strength. It is made mostly of XPS extruded polystyrene boards, PIR panels or polyurethane foam.
PIR panels are super efficient as a layer of insulation on the roof garden as they have special grooves as well as milled edge connections. These allow the rainwater to pass to drainage systems easily.
3. Drainage Layer
Drainage layer on your roof garden is used to quickly discharge the rainwater from the vegetation layer into the drainage system. It is also used to collect all excess water.
4. Geotextile Layer
Geotextile fabric layer is used to separate the drainage layer from the plants you will be growing in soil. This layer prevents depositing of soil and other fine particles which would otherwise clog the drainage system.
It also counteracts the reduction of water rapidly from the vegetation layer by circulating the moisture. Geotextile layer needs to be waterproof and vapor-permeable and also chemically and biologically resistant and robust.
5. Vegetation Layer
Vegetation layer is the growing medium, the surface where you’ll grow plants and all the plants themselves. The growing medium (soil) needs to have good air circulation and it should be water permeable.
The soil depends on the plants you’re growing. In general, plants require fertile and slightly acidic soil, which can be prepared by mixing garden soil, humus, farm manure or compost and organic matter.
The thickness of the growing medium also depends on the type of the plants you will grow in it.
Preparations for building a rooftop garden
Do not start any preparations before checking your city's building codes, your area, block and your building or house in particular. If there are no legal restrictions for building a rooftop garden, it’s important that you have a licensed professional check out the structural capacity of the building.
This is an important step which you need to make beforehand in order to assess whether or not the roof is stable enough to support the additional weight of a rooftop garden.
The expert assessment will also determine the type of rooftop garden design specific to your building and roof condition.
After that, start by checking out your roof to see how sunny and windy it is. This will determine the choice of plants which will thrive in those conditions. In general, you should primarily go for drought- and heat-tolerant plants, which do well on rooftops.
Next, draw a plan of your garden, including the positions of containers, pots and any garden furniture. Make a list of seeds or saplings to buy and before you know it you’ll be busy gardening!
What can you grow in your rooftop garden?
A rooftop garden is suitable for growing various shrubs, grasses, annuals, perennials, herbs, vegetables and even dwarf fruit trees. Everything except tall tree with long roots will be fine.
The choice of plants depends on what you want to grow, the climate in your area, your budget, the available space and the roof conditions.
Overall, the gardening opportunities are limited by the weight and height so you need to provide adequate support and enough weight bearing capacity for the soil, the plants, and the containers.
Types of rooftop gardening projects
Here are the two main types:
Rooftop Container Garden
The most common rooftop garden makes use of lightweight containers or raised garden beds. This design is very popular and easier to maintain. In addition, it offers more flexibility and is less expensive.
Rooftop container gardens are perfect for roofs with limited weight capacity and can fit any lifestyle or budget. Many items, such as containers, may already be on hand and readily available to all urban gardeners.
These might include plastic butter bowls, Tupperware containers, or similar items that are suitable for growing plants. Add some drainage holes and you get an inexpensive container.
Since weight issues can often be a factor in choosing appropriate containers for a rooftop garden, lightweight containers, such as these, are excellent choices. Fiberglass or wooden planters can also be used. If you want to save some time, most gardening containers and raised garden bed kits are affordable and widely available.
Lining the bottoms of containers with a lightweight material, such as peat or sphagnum moss, is another great idea.
Rooftop container gardens offer limitless options when it comes to rearranging or relocating your plants, especially during winter. If you want to save some time, you can buy which are readily available and affordable.
Green Roof Garden
This is a much more complex construction which involves turning the entire roof, or the majority of it, into a garden. A green roof garden needs layers to provide insulation, drainage, and a growing medium for plants.
Since this type of construction is more difficult to create, the assistance of qualified professionals is almost always required.
The first layer of the green roof is applied directly to the roof and serves the purpose of guarding the roof against leaks as well as providing insulation. The next layer contains lightweight material, such as gravel, which allows water to soak through while keeping the soil in place. The final layer includes both the growing medium and plants.
The growing medium – the soil
Whichever type of rooftop garden you go for, the growing medium should always consist of lightweight soil or compost. The soil application should also maintain a depth that will sufficiently anchor plants while fitting into the weight capacity of the roof as well.
In addition to being attractive, rooftop gardens are energy efficient and easy to care for, requiring little maintenance as long as you choose the right soil and monitor its properties and growing quality regularly.
When selecting the soil for a rooftop garden, you need to consider the average rainfall in the summer months, the average high and low temperatures during the growing season and the types of plants to be grown and their particular nutritional needs.
If you’re in an area with a lot of humidity and rain during the growing season, you need a media that dries out fast. In a dry environment, it is better to use a growing medium that holds water longer to minimize drought stress on plants.
How to build a rooftop garden - Step by step guide
Part 1 – Preparing your roof
Step 1- Check your city's building codes
You need to check your city’s building codes before beginning construction to make sure rooftop gardens are allowed in the area where you live. Your area might have restrictions on your garden's height, how you use your roof space, and whether certain decorations are too distracting.
Your building might be a part of a historical neighborhood in which case there might be strict regulations as regards changing the building in any way.
If you are renting your apartment in a building or a house, ask your landlord for permission before starting your rooftop garden.
Step 2 – Check your roof's loading capacity
A structural engineer must evaluate your roof's loading capacity so that you get the exact data on the load the roof can take. This load includes your plants, plant containers, furniture, equipment, visitors, but also weather loads like snow.
Based on the loading capacity you will be able to decide on the number of containers, planters, garden beds and the overall design of your garden.
Step 3 - Check that your building gets enough sun exposure
Depending on the plant, your garden may need as much as 6 to 8 hours of sunlight a day. Note the sunlight patterns over a period of at least one week to make sure the sunlight isn't obscured by other buildings.
Monitoring the sun in the morning, midday, and evening in order to get an accurate sense of how exposure changed throughout the day. This will matter a lot when you move on to positioning your containers.
Step 4 - Take the wind exposure into consideration
The wind is most often stronger on the rooftop than on the ground level, especially if your building has several stories. Too much wind can damage or even kill plants so structural windbreakers may be needed if you notice strong winds on your roof. Windy environment means more frequent watering as the wind will dry the soil faster. The best water hose is a must, just like with a regular garden. And a faucet nearby.
Step 5 - Map out your roof garden's design
Using graph or blueprint paper, make a rough sketch of your garden and decide where you want to put plants and furniture. This will help you to keep your rooftop organized when you begin building your garden. Keep the map on hand when shopping for containers, seeds, and accessories.
Part 2 - Buying the plants
Step 6 – Choose suitable plants for rooftop gardens
Stick to drought and heat-tolerant plants. The potentially strong wind and sunlight will make stronger plants more suitable than beautiful but fragile ones.
Stronger seedlings will be more likely to survive the first year. Add shade or windbreakers if you insist on more fragile plants. The staff in nurseries will help you with advice on which plants will suit your weather and roof conditions.
Ornamental grasses, honeysuckles, and magnolias all do well in hot, sunny
Make sure you regularly water your plants, even those that are drought-resistant.
Image titled Create a Rooftop Garden
Step 7 - Buy plants native to your area.
Plants originating from your state or climate will adapt more easily to your garden than non-native plants. In addition, they are more likely to attract native fauna, like birds and butterflies to aid the process of pollination.
Step 8 – Bear in mind the size of the plants
Choose ornamental trees and shrubs over larger plants which will weigh down your roof and leave less room for other plants. Small, ornamental trees and shrubs do well in rooftop gardens. This is especially the case if they are protected with windbreakers and placed in stable containers.
If you go for ornamental trees, make sure to trim your trees' roots every few years to keep them at a manageable size. Great ornamental trees and shrubs for rooftop gardens include Dogwood, Japanese Lilac Tree, Crabapple, Star Magnolia, and Jack Dwarf Flowering Pear.
As for other plants you can grow, please check our suggestions in the introduction.
Step 9 – Don’t go for large-leaf plants.
Plants with large, supple leaves tend to get shredded by the high winds on rooftop gardens. They are also more likely to suffer winter-burn during the colder seasons. Smaller-leaved plants or pines, on the other hand, thrive on rooftops.
Part 3 - Building your rooftop garden
Step 10 – Planning your plants’ watering needs
Unless you receive enough rainfall for a storage system, using a hose to water your garden will be most space-effective. Connect a hose that leads up to your rooftop. Check for a faucet or water line on the roof, and attach your hose.
If you can find neither, use the best watering can which is also light enough to carry around. The most reliable watering method involves setting up an automatic (timer controlled) watering system.
Step 11 – Adding containers or raised garden beds
Add containers for your plants or install raised garden beds, depending on your preferences. Refer to your garden map as regards the intended location of individual containers or flower/vegetable beds.
Step 12 - Planting seeds or seedlings
Depending on your preferences and skills, you can raise your plants from seeds or transplant young plants from nurseries. Seedlings are usually stronger and pest-resistant, while seeds are much cheaper.
Seedlings will have better chances to survive in cooler or windier climates. Alternatively, you can also plant the seeds indoors and transplant them outdoors later as seedlings.
Step 13 - Install trellis/windbreakers.
Windbreakers will keep your plants from drying out or getting damaged in a strong wind.
Trellises are a preferable option for rooftop gardens because they have holes, as solid windbreaks will be knocked over easily by the wind.
You can build or buy a trellis and decorate them with crawling ivy, sweet peas, climbing roses, morning glory or other suitable vining plants.
Part 4 - Decorating Your Garden
Step 14 - Add garden furniture and decorations
After you've finished planting, it’s time to bring in furniture and position it as planned. Go for lightweight furniture to avoid putting too much pressure on your roof. Foldable furniture, like lounge chairs, is really lightweight and good for conserving space.
To prevent the furniture from being blown away in heavy winds, secure it to immovable objects or store it inside when you’re not using it.
Step 15 - Make use of vertical space
Instead of crowding the ground level of your garden, use vertical space when possible. This will make your garden feel more spacious, so we recommend planting climbing vines or hanging smaller flower containers on adjacent walls if possible.
Now that your garden is completely set up, it’s time to pick a focal point which will tie your garden together. Choosing a centerpiece will make your garden feel balanced and harmonious.
A good focal point might be a larger plant, a statue, a smaller decorative tree or a lightweight foldable outdoor sofa where you can sit down and enjoy the view of your lovely green rooftop oasis.