Here is our guide to the types of green roofs, including the differences between comprehensive, semi-intensive and intensive green roof designs.
If you want something a little more environmentally friendly than your average roof, a good alternative is a green roof. These are also often referred to as eco-roofs, living roofs or vegetated roofs, and they incorporate vegetation into their designs.
Here we break down everything you need to know about implementing a green roof for your own space.
What is a green roof
A green roof is constructed with vegetation that completely or partially covers the surface. The plants lie over a waterproof membrane that often has different layers to ensure adequate drainage, insulation and growth.
The layers of a green roof generally consist of many different sections. It starts with a load-bearing roof that can withstand the weight of the green roof.
This is followed by the following layers: moisture barrier, insulating material, waterproof membrane, drainage, filtration, growing soil and plants. See more roof types here.
Extensive green roofs
The first type of green roof we will look at is comprehensive green roofs. If you are considering a green roof for a single family residential building or a small complex with few families, you will want to explore extensive green roofs.
These are often described both as low profile and as performance mode for a larger system. The main focus in comprehensive green roofs is to keep the weight low so smaller buildings and act as a basic structure without taking on unnecessary damage.
Types of Extensive Green Roofing Plants Used and Maintained
The plants included on an extensive green roof are chosen for two main reasons. First, consider what weight one of these buildings may have.
An extensive green roof means you need to carefully consider how much weight plants can add. This focuses on low weight plants that can thrive on a thin layer of growing medium.
In general, the most popular choices for extensive green roofs include sedums, moss, grass, herbs and succulents.
These are smaller, less heavy options that will spread your green roof up without adding weight that it cannot handle. In addition, it keeps your maintenance expectations low and manageable.
Extensive green roof depth
Of course, you need to consider the general dimensions of the roof. Yet the width and length of the roof is not this main focus in what is considered a comprehensive green roof relative to another option. Instead, this definition focuses in depth.
The depth of the average extensive green roof is only about three to five inches. In terms of the weight it comes with this depth, you can expect approx. 15 to 25 pounds per. Square foot.
Semi-intensive green roofs
Intensive green roofs and extensive green roofs both have their benefits. Conversely, they cater to both extremes. Where does a green roof fit into a building does not fit any of these options?
This is where semi-intensive green roofs come in. You can rely on this option when you need something that uses a bit of both concepts. While extensive green roofs are more of a living machine, and intensive green roofs act as a garden or park, these green roofs act as a small habitat.
Types of semi-intensive green roofing plants used and maintained
The plants used in semi-intensive green roofs usually include options such as sedums, ornamental grasses, small shrubs, herbs and selected perennials. Not all perennials will thrive in this size of environment.
In terms of maintenance, you can also expect a workload that falls in the middle. For example, you will want a partial irrigation system that you can use as needed instead of automatically using it as on an intensive green roof.
Semi-intensive depth with green roof
In a similar form as the rest of the concepts on this type of green roof, the roof depth sits between the average between a comprehensive and an intensive green roof.
The depth of a semi-intensive green roof is in a range of 5 to 7 inches. This adds a weight of approx. 25 to 40 pounds per. Square foot depending on construction and living components.
Intensive green roofs
Intensive green roofs are used more often on commercial buildings than on homes. We take a closer look at the concept of comprehensive versus intensive green roofs later, but intensive green roofs are known for their higher level of ongoing maintenance, care and a higher initial installation effort.
They also often have inorganic components in the design. This can include an option such as a table to sit at or a bench to chat with others on or just take plant life. Visit this page for more ideas for roofing.
Types of intensive roofing plants used and maintenance
The most important care you need to worry about for an intensive green roof is the installation of a professional irrigation system. This is because they often have several plants with a wider variety and thus varying needs.
On the other hand, due to the different plants in the design, you also need to pay close attention to their maintenance. This can include anything from ground cover like lawns or vegetables, flowers (especially perennials), shrubs, herbs, vegetables and in some patterns even trees!
Intensive green roof depth
Like the other options we have looked at so far, it is a crucial point to look at the specifications for an intensive green roof. This means looking beyond what you can grow on an intensive green roof to consider the space you need for this design.
For an intense green roof, you need a depth within a range of 7 to 24 inches. As for the weight of an intense green roof, plan for a range of 35 to 80 pounds or more per day. Square foot space.
Comprehensive vs. intense green roof
As we have covered, the two main types of green roofs are extensive and intensive options. When it comes down to it, though, what’s the biggest difference?
The biggest difference is how laborious they are. Extensive green roofs are easy to install and they do not require as much constant maintenance and care as irrigation. They are also the easiest option for a green roof.
Intensive green roofs, on the other hand, are more expensive and the most complex. They require a professional irrigation system and regular maintenance. On the other hand, these are considered “high-performance” options.
Layer of a green roof
When building a green roof, they are not a single layer. Instead, they are divided into a number of layers, each with its own meaning. These are built from the existing roof deck.
The first layer is to lay a waterproof membrane on your roof. That said, in retrofit situations, you may find that this layer already exists.
It may still be necessary to replace it if it is no longer waterproof. Common materials for this purpose include polyvinyl chloride (better known as PVC) and polymer-modified bituminous membranes.
The next step is to add a root barrier. This should be a flexible material but still be resistant to tears and punctures. This helps prevent roots from growing through the waterproof membrane, causing your roof to leak.
A protective mat is next and it is made to protect the previous layers from damage. On the other hand, it also acts as a reservoir for nutrients and water as well as for noise reduction.
The next layer is the drainage layer and it looks a lot like an egg carton but thicker. This works to retain the water that the plants need to thrive. However, the excess water is drained away through a built-in system that leads it to the roof drains.
The filter cloth is next, and it simply keeps the drainage layer and the growth medium – or, clearly, the soil – from washing away with the water.
This means that the medium is directly on top of the filter cloth. This usually includes soil, as mentioned, while it also includes mineral or organic additives to the mixture for extra nutrients.
Finally, you can add your green roofing plants. However, the exact plants you can add here vary. Specifically, you want to consider the climate of your region, the load capacity and budget of your tag in addition to your personal preferences.
For more eco-friendly designs, see our page on backyard greenhouse ideas.