Do you want to turn your once-abandoned rooftop space into one decked with plants, string lights, and benches? Your green roof won’t only revitalize your area and add to your home’s beauty but aid the environment by providing a habitat for wildlife and food for pollinators. And it will also reduce heat flux from roof to building by 72%. First, let’s understand the difference between rooftop gardens and green roofs.
The Difference Between Rooftop Gardens and Green Roofs
Green roofs are vegetated roofing systems grown over a waterproof membrane. And in contrast, a rooftop garden is a garden on your rooftop. In essence, a rooftop garden is a type of green roof.
Varieties of green roofs include intensive and extensive, and intensive green roofs include rooftop gardens. These have more than 6 inches of media and accommodate taller plants, while extensive green roofs have thinner soil layers (4-6 inches) and accommodate smaller plants. This makes them low maintenance.
Beyond improving aesthetics, green roofs act as insulation, help manage stormwater run-off, lower your building’s carbon footprint, and reduce the intensity of heat islands in urban settings. Note that heat islands contribute to higher daytime temperatures and air pollution with reduced nighttime cooling.
Building Your Green Roof
Here are the steps you should follow.
1. Assess Whether You Need Repairs
Before beginning, you need to assess if your roof can sustain the weight of the garden, is sturdy, and waterproof. If there are water leaks, blocked gutters, cracks, or damaged shingles, go for re-roofing or a complete roof replacement before working on your garden.
It is important to note that if your roof has 2 layers of shingles, building codes prohibit you from installing a third layer; you will need a full roof replacement in that case. Work with certified roofing professionals to do so.
2. Consider the Roof’s Angle, Weight, and Insulation
Flat surfaces are ideal for installing a green roof; however, for pitched or steep slopes, you need reinforcing systems or frames such as tray planting to hold soil in place. Green roofs can weigh between 60 to 150 kg per square meter; consult structural engineers to check if you need extra reinforcement. If your roof is over a conditioned space, go for insulation. Otherwise, you can opt for a layer of building felt for protection over a waterproof membrane.
3. Install Waterproof Layers
Add a waterproof layer over your shed to prevent leaks. You can go for a bitumen membrane or asphalt. Include a root barrier, such as a plastic sheet, to prevent roots from damaging the structure. Next, install a roof drainage membrane to ensure proper drainage into gutters and downpipes. It is better to get your roof professionally waterproofed.
4. Build a Frame
Use lightweight materials such as mesh gutter guards to build a frame and keep it at the same depth as your soil. Nail the corners together to hold the plants and soil in place. Add holes to the side of the frame to allow rainwater to drain.
5. Add Your Soil and Begin Planting!
Choosing Horticultural perlite and peat moss or shale-blended mixtures is preferable as they are lightweight and have good water drainage to grow your vegetation. Check with local nurseries for plants that grow the best in your area. As rooftop temperatures reach 150F in summer, you can pick succulents or cacti varieties for ground covers.
Your roof may need to be weeded twice or thrice a year for maintenance to prevent vegetation from clogging the drains. Make sure only to remove invasive plants, not cover crops or native wildflowers, as these are critical for soil health and a sound ecosystem where pollinators can thrive.
Being surrounded by nature under the sky and on top of your roof will be a peaceful experience, and building your green roof can fill you with personal satisfaction. You can do it yourself or have professionals work with you. However, as the cost may vary according to whether you chose intensive or extensive green roofs, the soil depth, the type of plants, and more, consider your budget and the material quality for your ultimate dream rooftop garden.