What is a Green Roof?

Roof with plants on the bottom half

Searching for an eco-friendly roof that will stand out? Consider a green roof. But what is a green roof?

Green roofs, also known as living roofs, provide unique natural beauty that makes them an eye-catching roofing choice. Not only do they add curb appeal with their attractive plants, shrubs and flowers, they also offer many benefits to homeowners and the environment.

What is a Green Roof?

A green roof system, also known as a living roof, is a vegetative layer of plant life growing over a waterproof membrane substrate. Unlike conventional roofs, the roof surface of a green roof is made up of a garden of plants. 

Green roofs date back to ancient times, the first prominent example being the Hanging Gardens of Babylon. The modern version of a green roof began in Germany during the 1960s. Since then, the green roof industry has become increasingly popular. Green roof technology has spread to other countries in Europe and around the world. 

The primary components of a green roof are the waterproof layer protecting the roof’s structure, the growing media, and the vegetative layer of plants that we see on top. Under that, there are multiple layers:

  1. Structural roof decking
  2. Vapor barrier
  3. Thermal insulation
  4. Root barrier
  5. Drainage layer
  6. Filter membrane
  7. Growing medium
  8. Vegetation layer

The waterproofing barrier shields the roof from water damage, protecting the roof decking from rain and other elements. 

Green roofs must be placed on flat or gently sloping roofs with no more than a 45-degree angle. 

Aside from a waterproof membrane, a green roof also needs a root barrier to protect the roof’s membrane from being damaged by growing plant roots. 

3 Types of Green Roofs

There are three main types of green roofs:


An extensive roofing system supports only a shallow planting system, typically no deeper than 6 inches

An extensive roof accommodates only plants with shallow roots such as:

  • Grasses
  • Mosses
  • Succulents
  • Wildflowers

Sedums are frequently used because they are a hardy plant capable of surviving in harsh conditions. 

Extensive roofs are fairly light, supporting 15 to 50 pounds of plant life per square foot. Aso, you are not able to walk on these roofs.

Aside from annual fertilization and weeding, extensive roofs don’t require much maintenance. Extensive roofs are generally left to grow and thrive without much landscaping.


Although they are more expensive, Intensive roofs support considerably more diverse vegetation than extensive roofs. They are deeper with a thicker soil layer than extensive roofs and can support as much as 80 to 150 pounds per square foot. 

Intensive green roofs allow owners to choose from a wide selection of plants:

  • Bushes
  • Flowers
  • Grasses
  • Mosses
  • Shrubs
  • Trees

Intensive roofs require more work. An intensive roof is like maintaining a garden in your backyard. They require regular care such as watering, weeding, and trimming. 

Depending on the size of the roof, intensive green roofs can be quite elaborate, hosting trees, shrubs, and even benches and walkways. They can function as recreational areas like a small garden or park.


Semi-intensive green roofs are a combination of extensive and intensive roofs.

Typically semi-intensive are accessible, like a mini-garden. They have more depth and hold larger plants than an extensive roof. Semi-intensive roofs have a deeper substrate than extensive roofs, but they aren’t quite as deep as an intensive roof

Semi-intensive green roofs require more maintenance than extensive roofs, although they also offer a wider range of plant types. 

Pros of a Green Roof

green roof
Photo Credit: Geograph

There are pros and cons of a green roof.

Here are some benefits of a green roof for both you and the environment: 

  • Reduce city heat
  • Provide insulation
  • Aid in stormwater management
  • Provide clean air
  • Last a long time
  • Great garden space
  • Reduce stress
  • Reduce noise
  • Contribute to biodiversity
  • Accommodate solar panels

Cons of a Green Roof

green roof
Photo Credit: Arlington County / Flickr / CC BY-SA 2.0

Green roofs have a few drawbacks: 

  • Expensive
  • Put weight on your home
  • Can cause roof damage
  • High maintenance
  • Limited plant options
  • Not ideal in some climates
  • Hard to detect roof issues

What to Consider Before Getting a Green Roof

There are several things to consider before getting a green roof:

  • Budget. Green roofs are costly, especially if you have to retrofit your roof. You should calculate if the installation and maintenance of a green roof is within your budget. 
  • Location. Make sure the local climate is suitable for the types of plants you’ve chosen. 
  • Roof type. Do you want an intensive, semi-intensive, or extensive green roof? You will need to decide what roofing type works best for you. 
  • Shade. Some plants don’t thrive in areas with a lot of shade. Before planting your rooftop garden, make sure that your plants on your roof will receive the right amount of sunlight.
  • Slope. Green roofs require a flat or low-sloping roof. Green roofs should not have more than a 45-degree angle. 
  • Weight. Green roofs weigh a lot, so buildings will need reliable structural support to support all the extra weight. 

Cost of a Green Roof

green roof
Photo Credit: Emmanuel Berrod / Wikimedia Commons / CC BY-SA 4.0

The cost of a green roof installation ranges from $13,000 to $50,000. The national average for the cost of a green roof is $15 to $50 per square foot.

No two roofs are alike, and the cost will vary depending on several factors:

  • Size
  • Shape
  • Slope
  • Location

Costs differ from the different types of roofs, as intensive green roofs are more expensive than extensive or semi-intensive green roofs. Consider the upfront cost in addition to the continuous maintenance costs. 

Some states and cities offer incentives to homeowners to encourage the installation of more green roofs. For example, New York offers tax abatements for green roofs, and Portland, Oregon, offers incentives for those with ecoroofs – another name for green roofs. 

FAQ About Green Roofs

Do you mow a green roof?

You do not necessarily have to mow your green roof, though it depends on what you want your green roof to look like. 

An extensive green roof is generally left to grow naturally on its own, so it will not need mowing. 

If your intensive green roof is a grass meadow, you might want to keep your grass trimmed. Accessibility will factor in, as well. Depending on the arrangement of your roof, it may not be feasible to get your lawn mower onto your roof. It is easier to mow a flat roof, but it is impossible (and dangerous) on a low-sloped roof.

How often do you replace a green roof?

Thanks to the protection of green roofs, the waterproofing membrane underneath the soil and vegetation needs to be replaced only every 40 to 50 years. 

What plants are best for green roofs?

Some plants won’t thrive in certain climates. In selecting plants for your green roof, consider how the local weather conditions will affect your rooftop plants. Your plant selection also will depend on whether you have an intensive, semi-intensive, or extensive roof

Here are some plants that work best on green roofs:

● Asters
● Birdsfoot trefoil
● Gold sedum
● Houseleeks
● Meadow saxifrage
● Oregano
● Sea thrift
● Two row stonecrop
● White stonecrop
● Widow’s cross
● Yarrow

Can I convert my traditional roof to a green roof?

It is possible to convert a traditional roof to a green roof. However, a green roof adds considerable weight to a home, so it will have to be retrofitted to ensure it can support the weight of a roof. 

You will need to consult a roofing professional about the project. Your roof also will need to be inspected to determine if it’s suitable for a green roof. 

Plan on Getting a Green Roof?

The natural beauty of a living roof offers many benefits. By reducing the urban heat island, managing stormwater runoff, and improving air quality, green roofs offer great benefits to your community. 

Green roofs provide personal benefits as well, such as insulation, noise reduction, long lifespan, and a recreational place where you can hang out. 
Do you want to get a green roof? Find a local roofing professional who can build a rooftop garden for you.

Main Photo Credit: Ryan Somma / Flickr / CC BY-SA 2.0

Danielle Gorski

Danielle Gorski lives with her family in Texas. She has a degree in Professional Studies and a minor in marketing. Her hobbies include reading, drawing, and writing.