What Is a Green Roof? (2023)

A green roof, also known as a living roof, is a roofing system that involves covering the roof of a house with vegetation, such as plants and grass, over waterproofing membranes. Green roof houses may also include additional features like drainage systems, root barriers, and irrigation systems [[SOURCE 1]].

Different Types of Green Roof Systems

There are two main types of green roof systems: extensive and intensive.

Extensive Green Roof System: An extensive green roof can hold up to 25 pounds of vegetation per square foot. These roofing options have a shallow build-up height and are lightweight. They are best suited for herbs, sedum spices, and grasses. Extensive roof systems are designed to withstand wind, drought, sun, and other natural conditions. Maintenance for extensive green roofs is relatively low, typically requiring only one to two inspections per year [[SOURCE 1]].

Intensive Green Roof Systems: Intensive green roofs are more accessible and multifunctional, often resembling a garden roof. They require more weight and a deeper build-up system. Intensive green roofs require regular maintenance and can vary depending on the landscape design and plant material. With intensive green roofs, you can grow perennials, trees, shrubs, and lawns, depending on the substrate depth. Intensive green roofs can also include additional features like pergolas, ponds, driveways, and walkways [[SOURCE 1]].

Both extensive and intensive green roof systems have a layering system that establishes a base for planters using mats, soils, and various materials to retain nutrients and remove waste by-products [[SOURCE 1]].

Green Roof Benefits

Green roof houses offer various benefits that can improve both your home and the surrounding community. Some of the key benefits include:

1. Improve the drainage system: Green roofs contribute to sustainable drainage, which helps counter flooding during excess rainfall. Water is stored in the substrates and plants before being released naturally into the environment. This helps prevent flooding and reduces the strain on urban drainage systems [[SOURCE 1]].

2. Increase the lifespan of the roof: Green roofs act as a protective barrier for the underlying waterproof membrane, extending the lifespan of the roof by at least three times. The vegetation helps shield the roof from harsh climatic conditions, such as rain, wind, fluctuating temperatures, and UV rays [[SOURCE 1]].

3. Boost thermal performance: Green roofs have a significant impact on thermal performance. They provide insulation, reducing heat loss during winter and minimizing heat gain during summer. This can lead to energy savings and improved comfort inside the house. The plants on the roof absorb the sun's energy, reducing roof temperatures in summer and aiding thermal efficiency in winter by trapping heat inside [[SOURCE 1]].

4. Help the environment: Green roofs play a role in reducing carbon dioxide emissions, a major contributor to global warming. They help reduce the need for air conditioning, which in turn reduces energy consumption and CO2 emissions. Additionally, green roofs contribute to biodiversity and create a habitat for wildlife, supporting a healthier ecosystem [[SOURCE 1]].

5. Improve air quality: Green roofs help improve air quality by reducing air pollution. They absorb pollutants like sulfur dioxide and nitrous acid, which are major contributors to poor air quality in urban areas. Studies have shown that green roofs can reduce sulfur dioxide by 37% and nitrous acid by 21% [[SOURCE 1]].

Disadvantages of Green Roofing

While green roofs offer numerous benefits, there are also some disadvantages to consider:

1. High maintenance: Green roofs require regular maintenance, including watering, weeding, and monitoring for plant growth and potential issues. This can be time-consuming and may require additional expenses for professional maintenance services [[SOURCE 1]].

2. Potential for damage: The weight of a green roof can put additional stress on the structure of the house. If not properly designed and installed, it can cause sagging or other structural issues. Additionally, plant roots can potentially damage the roof, leading to costly repairs [[SOURCE 1]].

3. Insurance and liability: Due to the potential risks associated with storms and droughts, insurance for green roof houses can be expensive. It's important to consider the potential liability issues that may arise from the weight and maintenance requirements of a green roof [[SOURCE 1]].

The Cost of Green Roof Systems

The cost of installing a green roof can vary depending on several factors, including the type of green roof system, the amount of vegetation, and the materials used. On average, the cost ranges from $10 to $25 per square foot. Extensive green roofs tend to be less expensive, while intensive green roofs can be more costly due to the additional weight and maintenance requirements [[SOURCE 1]].

It's important to consider the long-term maintenance costs when budgeting for a green roof project. Maintenance costs can range from $0.75 to $1.50 per square foot annually. Some companies may offer free maintenance for a certain period, but it's essential to factor in ongoing maintenance expenses [[SOURCE 1]].

Design Standards for Green Roofs

When installing a green roof, there are three key design standards to consider:

1. Wind uplift: Wind uplift can cause damage to both the house structure and the green roof. To prevent this, the RP14 Wind Design Standard was created for vegetative roofing systems. It provides guidelines and recommendations to protect the green roof from wind-related issues [[SOURCE 1]].

2. Fire safety: While green roofs provide some fire retardation, there is still a risk of fire due to natural events. The VF-1 Fire Design Standard for Vegetative Roofs helps minimize this risk by providing guidelines for fire-safe designs and mandatory maintenance regimens [[SOURCE 1]].

3. Root damage: Plant roots can potentially burrow into the house rooftop, compromising the structure and causing damage. It's important to consider root repellent systems and take preventive measures to protect the roof from root damage [[SOURCE 1]].

Installation Process of Green Roof Systems

The installation of a green roof system is a complex task that requires skilled contractors. Here is a general overview of the installation process:

1. Structural assessment: Before starting the installation, a structural engineer should assess whether the building or home can support the weight of the green roof. This is crucial to ensure the roof structure is strong enough to handle the additional load [[SOURCE 1]].

2. Roof pitch: Determine the pitch of the roof to facilitate proper water drainage. A minimum slope of ¼ inch per foot is recommended to prevent water accumulation and potential damage to the green roof system [[SOURCE 1]].

3. Plant trays: Grow the plant trays at least four months prior to the installation. This allows the vegetation to establish properly. Plant trays can be purchased and shipped, ensuring they are protected during transportation [[SOURCE 1]].

4. Protective edgings: Install protective edgings along the roof perimeter to contain the green roof system. These edgings help prevent soil erosion and provide a defined boundary for the vegetation [[SOURCE 1]].

5. Tray installation: Start installing the plant trays from the lowest section of the rooftop, working in rows. For slanted roofs, contractors may start working in an inclined direction. Attach the trays together using plastic lips on the tray edges to secure the green roof system. Trim the final tray in each row to ensure a tight fit and uniform coverage [[SOURCE 1]].

6. Soil elevators removal: Remove the soil elevators, which were used to moderate the height of the plants during transportation. This allows nutrients, water, and healthy organisms to flow between the planters [[SOURCE 1]].

7. Edging and watering: Secure the edging to the roof and ensure proper water supply for the plants. Regular watering is necessary to help the plants settle into their new home [[SOURCE 1]].

Final Words

A green roof system, also known as a living roof, offers numerous benefits for both individuals and the community as a whole. From improving drainage systems and extending the lifespan of the roof to boosting thermal performance and supporting wildlife habitats, green roofs have become a popular choice for environmentally conscious homeowners. However, it's important to consider the maintenance requirements, potential disadvantages, and design standards when planning to install a green roof. By understanding the costs and following proper installation procedures, you can create a sustainable and beautiful living space that contributes to a greener future.