Green Roofing System

A green roofing system uses a combination of waterproof membranes, drainage mats and growing medium to create a “living roof” upon which plants can grow.  They have become very popular in recent years and can give a property a very distinctive and interesting look.  Homeowners can add their favourite plants to their roof and obtain a strong roof that lasts for many decades.

But how does a green roofing system actually work?  This article will take a look at the advantages of green roofing systems before explaining how they work and what happens when they need repairs.

Advantages of a Green Roofing System

There are a number of significant environmental and energy saving advantages gained from having a green roof.  They include:

Green Roofing Systems Have Excellent Thermal Performance

Green roofing systems are constructed from layers of different materials including soil, separation fabric, granular drainage, root barriers and waterproof membranes.  The combination of these layers is usually between 4” and 20” thick.  When the roof is populated with plants, it will also contain water, trapped air, roots and insects.  

All of these materials combine to become a very effective form of insulation.  Additionally, the plant processes (photosynthesis and evapotranspiration) and soil processes (evapo-transmission) reduce the amount of solar energy that the roof absorbs.

In summer, that means your home will be much cooler.  You will be less reliant on air conditioning and potentially save a significant amount of money on energy costs.  In winter, it means your heating system is more effective because the warm air will not escape through the roof.

Excellent Sound Insulation Properties

For the same reasons that green roofs have excellent thermal properties, they also reduce the amount of noise coming into or leaving your home.  The growing medium is excellent at absorbing and deflecting sound waves.  If you live in a noisy urban area, this is a huge benefit!

Green Roofs Help to Overcome The Urban Heat Island Effect

In urban areas, the large amount of concrete and pavement can increase the temperature of your local environment.  A green roof will absorb a great deal of that heat and help to overcome the heat island effect.

They Improve Air Quality

The plants on a green roofing system can absorb carbon monoxide, carbon dioxide and other pollutants from the air.  That helps to make the air you breathe cleaner and healthier.

They Help to Support Biodiversity and Save Water

Plants on a green roof will attract all sorts of wildlife, including bees, birds and butterflies.  You will be helping to support the local environment and give all kinds of animals a beautiful location to reside.  Green roofs also reduce the amount of water that flows into the stormwater drains by absorbing it.

Anatomy of a Green Roofing System

A green roofing system has several layers, which can vary depending on the installation company and the types of plants being used.  Typically they will include (from bottom to top):

  • A Substrate Level - The bottom level often consists of plywood or a similar material that is attached to the roof.
  • Waterproof Membrane - A strong rubber or plastic layer designed to stop water
  • Drainage Layer and Root Barrier - This is typically a layer of dimpled plastic sheets that stop roots from penetrating any further and stores water.  It may also allow excess water to be drained from the roof.
  • Filter Fabric - This stops small particles from clogging the drainage system
  • Irrigation System - Some green roofs have an inbuilt irrigation system to provide water when there hasn’t been rain for a long period.
  • Growing Medium - This is typically a lightweight soil blend that may contain perlite.
  • Erosion Control Blanket - If your home is exposed to occasional torrential downpours, this biodegradable blanket can help prevent erosion while the plants get a chance to root.
  • Plants - Your unique collection of plants!

Green Roofing System Repairs

A well installed green roofing system will last a very long time — as long as 50 or 60 years!  Green roofs last a long time because the growing medium and plants absorb the brunt of the weather.  The plastic waterproof membrane is protected from ultra violet light by the layers above it and will last for decades.  

The longevity of a well-installed green roofing system is far beyond most other types of roofs — the key is to use a professional and experienced green roof installer.  

In the unlikely event that a green roof does begin to leak, repairing it will involve removing the layers above it and adding a new water proofing membrane.  Because of the many advantages of green roofing systems, they are expected to become far more common in the coming years.