Extensive and Intensive Green Roof - What Is the Difference?

Green roofs have recently become a popular addition to buildings and skyscrapers all over the world. They can help reduce energy use, manage rainwater, and improve air quality.

There are two types of green roofs: intensive and extensive green roofs. 

Both types can include beautiful green rooftop gardens but differ in design, maintenance, and purpose. 

Extensive green roofs are more lightweight and need less care. Intensive green roofs are more like traditional gardens and need more attention.

Knowing the differences between these two types of green roofs can help you choose the right solution for a building.

If you can't decide between an extensive and intensive green roof, this article will help you make that decision.

What Is an Extensive Green Roof?

An extensive green roof is a type of green roof system installed on top of buildings. 

They're primarily focused on providing environmental benefits rather than serving as a space for human use.

Since extensive green roofs are usually shallower than 250mm, they're lightweight. They also need less maintenance.

They can also manage stormwater, and they even provide insulation.

Extensive green roofs can include a wide variety of plants, supporting biodiversity. For instance:

• Sedums
• Grass
• Herbs
• Moss
• Succulents
• Wildflowers
• Small shrubs

These types of plants must be able to thrive in shallow substrates. They help the roof remain sustainable, visually appealing, and functional with minimal maintenance.

These sustainable roofs demand minimal upkeep, offering lasting environmental benefits. They're great for urban areas that have limited support. 

What Is an Intensive Green Roof?

Intensive rooftop gardens are typically deeper than 250 mm. So, they offer more space for deeper substrates and a diverse plant life. 

These types of roofs often serve as usable outdoor spaces. 

Intensive green roofs are designed for supporting a wide variety of plants, just like traditional gardens or parks. These plants can include:

• Perennials
• Grass and sedges
• Shrubs
• Herbs
• Trees
• Vegetable and fruits
• Vines and climbers

Intensive green roofs offer the flexibility to plant more vegetation. But because of this, they need regular maintenance and irrigation. 

This also means they are harder to install, and more expensive as well. 

Unlike extensive systems, they are more aesthetically pleasing and nicer to look at. However, they have higher maintenance needs and require safe access so the space can be maintained.

They are ideal for buildings that can withstand heavier weight loads.

Extensive vs. Intensive Green Roof

When installing a green roof, building residents usually aren't sure which type to choose - extensive green roof vs intensive green roof.

The design and installation of a green roof is a major investment and there is a lot of professional input required to achieve a successful outcome.

You should know all the answers before making up your mind. 

Here are the main differences between extensive and intensive green roofs:

1. Depth and weight loading of roof space
2. Vegetation
3. Maintenance
4. Use and accessibility
5. Installation costs and ongoing maintenance costs

Let's take a closer look at the main differences between these two types of green roofing solutions.

Depth and Weight

The key difference between an extensive and intensive green roof is their depth and weight. 

Extensive green roofs have a shallower substrate, typically shallower than 250mm. 

Because of this shallow depth limit, these types of green roofs can only tolerate smaller plants. For instance, mosses, sedums, herbs, grass, and small shrubs.

Extensive roofs are lighter in weight. They also place less stress on the building structure if weight loading has been identified as an issue.

Because of the shallow substrate and limited plant mass, extensive green roofs are much lighter than intensive green roofs. 

This makes them suitable for a wider range of buildings, including those with less structural capacity to support heavy loads and retrofitting of existing roof spaces.

Intensive green roofs have a deeper substrate, typically deeper than 250mm.

The depth can vary significantly, allowing for a wider range of plants, including shrubs, trees, and lawns. 

Because of the deeper substrate and larger plants, intensive green roofs are much heavier. 

This added weight requires that the building's structure be specially reinforced to support the extra load.

Vegetation

An extensive and intensive green roof also differs in vegetation types.

Extensive green roofs have a shallower substrate layer. This limits plant selection to low-growing, hardy species that can thrive in thinner substrate layers. 

The plant selection for extensive green roofs usually includes hardy, low-maintenance species. For instance, sedums, mosses, herbs, succulents, and grass.

These plants are chosen for their ability to thrive in a shallow substrate. They can also withstand exposure to harsh rooftop conditions. 

These could include high winds, intense sunlight, and temperature fluctuations.

The variety of vegetation on an intensive green roof can be extensive. This can be everything from small plants like flowers and herbs to larger vegetation like bushes and small trees. 

Because of the deeper substrate, intensive green roofs can support a more diverse and complex range of plants. 

For instance, perennials, shrubs, small trees, and even vegetable gardens. 

This diversity allows for the creation of complex landscapes, like those found in ground-level gardens and parks.

Maintenance

Another important difference is maintenance requirements.

Extensive green roofs are designed to be low-maintenance. They often need minimal intervention after the initial establishment period.

They are typically self-sustaining. This may include the occasional:

• Weeding
• Fertilising
• Irrigation during prolonged dry periods
• Seasonal clean-up

But, in general, these roofs need little ongoing care to remain healthy but will require regular visits to ensure plant health and functioning of the roof space. 

Intensive green roofs need more maintenance, just like a traditional garden. 

The reason why these types of gardens need more work is because of the diverse range of plants.

The type of maintenance needed can include:

1. Regular watering
2. Weeding
3. Fertilising
4. Pruning and trimming
5. Sometimes mowing 
6. Substrate management 
7. Drainage maintenance
8. Replanting
9. Pest and disease control

Maintaining an intensive green roof involves a combination of regular and seasonal tasks.

Irrigation systems are often installed to help maintain plant health. This is especially important during dry periods.

Use and Accessibility

You may not know this, but intensive and extensive green roofs actually have different uses. 

Extensive green roofs are typically not designed for regular use. In fact, they are often inaccessible except for maintenance purposes. 

Their primary functions are ecological.

This includes stormwater management, insulation, and reducing the urban heat island effect.

So, technically speaking, they are only for looking at and enjoying the view. They are great for neighbouring dwellings and office spaces to look out onto.

Intensive green roofs are often designed as accessible spaces. These tend to be rooftop gardens where people can walk, relax, and even host events. 

They can be a functional extension of the building's usable space.

This is what makes intensive green roofs more like traditional gardens and parks. 

Cost

The final difference between an extensive and intensive green roof is the cost.

Extensive green roofs are more cost-effective because of their lighter weight, simpler planting schemes, and lower maintenance requirements.

They are more cost-effective to install and maintain compared to intensive green roofs.

Intensive green roofs need more structural support and ongoing maintenance. That's why installing them is a more costly investment. 

Of course, there are various factors that can influence the price, such as:

1. Roof size
2. The complexity of the project (accessibility, ability to deliver materials to roof, etc.) 
3. Location of the building
4. Structural requirements
5. Required materials 
6. Plant selection
7. Irrigation system
8. Long-term costs

Despite these varying factors, intensive roofs are always going to be more expensive to install and maintain than extensive green roofs. 

What Is the Next Step?

Have you made a decision on what type of green roof you want? The next step is to find a green roof contractor you can trust. 

Evergreen Infrastructure is a green spaces consultant offering a wide range of services, including green roof design, installation and management.

We have experience with both intensive and extensive green roofs, and we can advise you on which option is a better fit for your roof. 

With cutting-edge technology, customised solutions, and innovative ideas, we are here to transform your plain rooftop into a beautiful, lush paradise.

Contact us if you want to know more about our green roof services. 

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