Everything You Need to Know about the "Green Roof" Movement

green roof-Reed College, Oregon.jpg

Considering Sustainability and A Green Roof

Thinking about becoming more eco-conscious in the way you live? Sustainability is a practice that you can incorporate into your green space that can help you to live in a more eco-friendly way. From planting drought-resistant plants that require less watering to eliminating evasive species and replacing them with native plants, every little action you take can work to lessen our impact on the environment.

One bigger action you might be interested in taking is adding a “Green Roof.” Retrofitting your home, garage or shed with a green roof can provide you with benefits, like keeping your home cooler in the summer and warmer in the winter, meaning lower energy use. A green roof can also be made very aesthetically attractive, adding to your home's curb appeal, or even used to grow food.

Here’s a look at what constitutes a green roof, the three different types, the benefits of installing a green roof and how to choose the right green roof to meet your needs.

What Exactly is a Green Roof?

A green roof consists of a layer of vegetation planted over a waterproofing system that is retrofitted on top of a flat, or slightly-pitched roof. The green roof takes advantage of what’s been learned about growing plants in soilless mixes to create a garden weighing substantially less than one using actual soil.

Also, known as eco-roofs, or vegetative roofs, there are three main types. An extensive green roof has a shallow growing medium - typically less than six inches, a modest roof load, limited plant diversity, minimal watering needs - and is often not accessible to users. In addition to climate control, its value to the homeowner is the visual pleasure of the garden’s design.

An intensive green roof has more soil and a deeper growing medium, sometimes as deep as several feet. That means the green roof can support more diverse plant choices, including small trees. It also needs more maintenance and watering. It is typically accessible and can even be used for growing vegetables and fruits or used for recreation.

A semi-intensive green roof uses the characteristics of both extensive and intensive roofs. The best choice depends on a number of factors like the structure of the roof, the plants you choose, annual rainfall, and stormwater performance needs.

The Advantages and Disadvantages of a Green Roof

Both extensive and intensive green roofs have specific advantages and disadvantages. The extensive green roof is lightweight, suitable for large areas, and can be installed on roofs with as much as a 30-degree pitch and low maintenance.

There's typically no need for any irrigation or drainage system, and it's relatively easy to install. Typically, extensive roofs are retrofitted on existing structures and are relatively inexpensive. They also look more natural, and because they require little or no structural adjustments, extensive green roofs are easier to get the necessary building approvals.

Since intensive green roofs feature a deeper growing medium, they also need irrigation and drainage systems to accommodate the diversity of plantings. Because of their depth, they can offer insulation benefits, meaning you'll use less energy heating and cooling your home. 

The disadvantages are minimal. The extensive green roof has a limited choice of plants that will thrive. There's also typically no or limited access, so it is not appropriate for growing food, or recreational use.

The intensive roof has a much larger weight-load, so you may need to include structural adjustments and an engineer to your budget. The use of irrigation and drainage systems also means higher energy use, water use, and more materials. An intensive roof should only be installed by a certified professional due to the complexity of the construction.

All three types require specific construction with different layers of materials not found on a typical roof. The basic green roof consists of: (from top to bottom)

• vegetation
• growing medium
• filter membrane
• drainage layer
• waterproof/root repellant layer
• roofing membrane support
• thermal insulation
• vapor control layer
• structural roof support

Each layer performs a specific function in the system, from keeping the plants alive to structural protection.

Choosing The Right Green Roof

When it comes to choosing the right green roof, consider first the available space and your goals. For example, small-scale green roofs are perfect for placing under your main roof – think porch roof, garage roof, or on the shed. 

Determine whether your green roof will be extensive, intensive or a hybrid. An extensive roof typically needs less maintenance. While an intensive roof will have more layers and require more care, the place you choose to build will help you to make this decision. 

The best solution is to speak with a landscape architect who works with green roofs, especially if your roof is pitched over 10 degrees, or under 2 degrees. They can help you to strategize the design to meet your needs. The condition of the roof itself must be taken into consideration as well. Only roofs that are leak free, and in good solid condition should be considered. A small green roof can weigh between 13 and 30 pounds per square foot before saturation. Your specialist should take structural considerations into account when designing your green roof. 

Here are two links to learn more:


A green roof is an affordable way to add curb appeal while contributing to a healthier environment. What do you think?

Ann Yakimovicz