Green Roofs

Green Roofs are also known as Living Roofs or Eco-Roofs.

Sods or plants are used a well-researched sustainable design methodology to provide a water tight, sustainable roof surface. Whilst green roofs are common in under-developed countries, their introduction to the modern building practices is providing an exciting new development in the sustainable building movement, and gaining in popularity across the world.

Types of Green Roofs

There are two basic types of green roof:

• Intensive Living Roofs - using plants between 1 to 15 feet high, including shrubs and trees. This type of planing requires deep levels of soil, and thus a heavy weight-loading roof. Due to the high level of ongoing maintenance and extensive irrigation required, this type of green roof is generally not suitable for domestic buildings.
• Extensive Living Roofs - use only low-lying plants from 2 to 6 inches high. Only a few inches of soil is needed - and only a low weight-loading roof. Plants are specifically selected for their sunlight tolerance and low maintenance.

Both types of green roofs can be used for flat or pitched roof construction up to 45 degrees. Sloped roofs require design elements to allow for impact on drainage and soil loss.

Constructing a Green Roof

A green roof system consists of layers to allow for a natural growing environment whilst also protecting the building and roof. There are four main layers:

• Standard metal roof top
• Waterproof membrane
• Root repellent membrane
• Filter cloth -to allow water to drain but prevent soil escaping
• Foam - creates a moisture blanket to ensure sufficient water retention for plant life
• Drainage system - to drain excess water
• Soil substrate - recycled aggregates such as crushed porous brick
• 4 inches of lightweight and free draining soil with good moisture retention properties
• Native plants

Video - Green Roof Construction [3:00]

Suitable Plants

Plants should be low growing, rapid spreading, drought-tolerant, with a fibrous root system (to protect roof membranes). They should also require low nutrient levels to minimise care.

Allergen free native species are ideal, as are short perennials, wildflowers and succulents.

Benefits of Green Roofs

There are a number of social, economic and environmental benefits to green roofs, including:

• Increasing home energy efficiency - cooling in summer, insulation in winter
• Moderate temperature - lowering overall ambient air temperature outside as well as moderating the heat within the home.
• Filtering and cleaning toxins from both air and water
• Attract local bird life - preserving and enhancing biodiversity
• Reducing carbon dioxide emissions
• Retain rainwater before it evaporates - reducing flooding
• Reducing urban temperatures and associated smog
• Insulating against sound / noise
• Providing aesthetic appeal and 'green space' recreational opportunities
• Using recycled materials like aggregates and plastic sheets

Green roofs are growing in popularity, with over 10% of houses in Germany with green roofs. Many countries are integrating green roofs into their building standards and regulations. Some even provide subsidies and incentives.

With current growth of 10-15% in Europe, and increasing interest worldwide, green roofs are becming an increasingly important option for builders and planners.

Next: Green Cladding Materials

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