Understanding Green Roof Weight

Are you thinking about installing a green roof? If so, you might have thought about how much it will weigh. 

Green roof weight is something you definitely need to consider before you take that step.

The weight of a green roof affects everything from the building's structure to its maintenance.

A roof must be strong enough to support the extra load. If it isn't, it could lead to safety risks or building damage. 

Knowing the weight also helps meet local building codes and requirements.

This article explains how much a green roof weighs. It also looks at what affects that weight and why it matters.

Types of Green Roofs and Their Weight

Green roofs are a popular solution for making buildings more eco-friendly. 

They offer a range of benefits for both the environment and the community. Some of the key advantages include:

• Energy savings
• Reduced stormwater runoff
• More opportunities to create green spaces in cities
• Better air quality
• Improved physical and mental health
• Higher property values
• Improved biodiversity
• More spaces to build communities

There are two main types of green roofs: extensive and intensive. Each has a different design, plant selection, and level of maintenance. 

The biggest difference between them is how much they weigh and what kind of plants they can support. 

Knowing the weight is important when planning a green roof. This is especially true for older buildings or ones with limited structural strength.

Extensive Green Roof Weight

Extensive green roofs are the lighter option. They're designed to be lightweight and easy to care for. 

These roofs have a thin layer of growing media, usually shallower than 250mm. 

The growing media is just deep enough to grow small, hardy plants like:

• Sedum
• Moss
• Wildflowers
• Short grasses
• Succulents

These plants don't need much water or maintenance. This makes them great for people who want the benefits without too much upkeep.

One of the main reasons people choose an extensive green roof is its light weight. 

When fully soaked with water, the roof can weigh between 50 and 170 kilos per square metre. 

Because of this, it's a good option for buildings that were not originally built to hold extra weight. 

Extensive roofs are also more affordable to install. 

They don't need special access or complex irrigation systems. This makes them a popular choice for:

• Residential homes
• Garages
• Small office buildings

Even though they are thinner and simpler, extensive green roofs still offer benefits. 

They keep buildings cooler, reduce energy use, and help manage rainwater. 

In urban areas, they can also support pollinators and small wildlife. So, even though they're light, they pack a lot of value.

Intensive Green Roof Weight

Intensive green roofs are much heavier and more complex. They're designed to hold many types of plants, including:

• Flowers
• Shrubs
• Small trees
• Vegetable gardens
• Perennials
• Vines and climbers

To support this, they need growing media deeper than 250 mm. Because of this depth, they hold a lot more water and plant roots, which adds to the total weight.

A fully watered, intensive green roof can weigh anywhere from 200 to more than 730 kilos per square metre.

That's a big load, so the building must be specially designed or reinforced to support it. These roofs also need more care. 

They often need irrigation systems, drainage layers, and regular gardening to keep the plants healthy. 

In most cases, they also need safe, easy access so workers can perform maintenance.

While they cost more and need more planning, intensive roofs offer a lot in return. 

They can turn rooftops into full gardens or parks, giving people a space to relax or even grow food. 

They also provide better insulation and can last a long time when well cared for. In cities, they add beauty and green space where it's often missing.

Intensive green roofs are best for new buildings or large commercial spaces. 

But when done right, they offer benefits that go beyond those of a standard roof.

Factors Influencing Green Roof Weight

The weight of a green roof depends on many parts of its design. 

Each layer, plant choice, and added feature can change how heavy the roof becomes. Knowing these factors helps you plan for a safe and lasting green roof.

The factors that influence green roof weight include:

1. Growing media depth 

Growing media is the main source of weight on a green roof. The deeper the media, the more it weighs, especially when wet. Shallow media layers, like those on extensive roofs, are lighter. Deeper media, used for sturdier plants on intensive roofs, adds much more weight.

2. Water retention

Green roofs soak up rainwater. It stays in the growing media and drainage layers, making the roof much heavier when wet. Roofs with more layers to hold water can be useful for managing stormwater. However, they increase the load on the building.

3. Plant type

Different plants require different growing conditions. Small plants like moss or sedum are light and need little growing media. Larger plants like shrubs or trees need more media, more water, and more care. These choices can raise the total weight of the roof.

4. Drainage and support layers

A green roof includes more than just plants and growing media. It also needs drainage layers, root barriers, filter fabric, and sometimes insulation. Each of these parts adds extra weight. Stronger drainage systems and protective layers may be necessary on larger, more complex roofs.

5. Weather conditions

Heavy rain can soak the growing media and quickly increase the load. Hot, dry conditions may not add weight, but they affect how often the roof needs watering. Irrigation systems and water storage layers can also raise the total weight. In coastal areas, strong winds may need extra anchoring systems, which adds to the load as well.

6. Maintenance features

Some green roofs include walkways, planters, benches, or irrigation systems. These features can improve how the roof is used, but they also add extra weight. Any extra structure on the roof must be counted in the total load.

Why Is Green Roof Weight Important?

Knowing the weight of a green roof is key for safety and success.

It affects how the roof is built, how long it lasts, and how well it works. Ignoring the weight can lead to damage, costly repairs, or even danger to the people who live there.

It's important to know the weight of your green roof because of these considerations:

1. Structural safety

Every building has a weight limit. A green roof adds extra load, including the growing media, plants, and water. If the roof is too heavy, it can cause cracks or sagging. In the worst case, it could lead to roof failure. Before adding a green roof, a builder or engineer must check if the structure can handle the extra weight.

2. Design planning

Different roof types have different weight needs. An extensive green roof is much lighter than an intensive one. Knowing the weight helps builders choose the right materials and support systems. It also helps them plan for extras like walkways, railings, or water tanks.

3. Cost and maintenance

Heavier green roofs often need stronger support, which can increase the building cost. They may also need regular care, like watering or trimming. Planning for the right weight means fewer surprises later. It also helps avoid damage that could come from overloading.

4. Weather readiness

In places like Australia, where rain, heat, and wind vary, weight can shift. Wet growing medial is heavier than dry soil. Adding features to deal with drought or wind can also add more weight. Planning for these changes keeps the roof safe in all seasons.

5. Building code compliance

In Australia, green roofs must follow local and state building codes. These codes help make sure the roof can handle the extra weight. They also check that the design includes proper drainage, waterproofing, and fire safety. Before starting, you or your builder will need to submit plans to the local council. If it meets the regulations, you'll get feedback regarding the project and then a permit to begin construction.

Choosing the Right Green Roof for Your Project

Green roofs are a smart and sustainable way to improve both buildings and the environment. But for a green roof to work well, planning is key, especially when it comes to weight.

Things like growing media depth, plant choice, weather, and extra features all affect the weight of the roof. Knowing how much weight your building can support keeps the structure safe. 

If you're planning a green roof, it's best to work with experts who understand every step—from design and weight to permits and upkeep.

Evergreen Infrastructure is ready to help. 

We are leaders in green roof design and installation. Whether you're building a small garden or a full rooftop landscape, our team offers the support you need from start to finish.

Ready to get started? Contact Evergreen Infrastructure today and bring your rooftop to life.

{{cta}}