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DOES A GREEN ROOF HELP?

January 25, 2010

DOES A GREEN ROOF HELP?

By Lorraine Cyr

YES!      YES! A MILLION TIMES YES!

Especially in cities.  By lowering air-conditioning demand, green roofs can reduce air pollution and greenhouse gas emissions that lead to global warming.

Wikipedia defines a green roof as:

A green roof is a roof of a building that is partially or completely covered with plants and soil, or a growing medium, planted over a waterproofing membrane. It may also include additional layers such as a root barrier and drainage and irrigation systems. (This term does not refer to roofs which are merely colored green, as with green roof tiles or roof shingles.) Container gardens on roofs, where plants are maintained in pots, are not generally considered to be true green roofs, although this is an area of debate. Rooftop ponds are another form of green roofs which are used to treat greywater. Also known as “living roofs,” green roofs serve several purposes for a building, such as absorbing rainwater, providing insulation, creating a habitat for wildlife, and helping to lower urban air temperatures and combat the heat island effect. There are two types of green roofs: intensive roofs, which are thicker and can support a wider variety of plants but are heavier and require more maintenance, and extensive roofs, which are covered in a light layer of vegetation and are lighter than an intensive green roof. The term green roof may also be used to indicate roofs that use some form of “green” technology, such as a cool roof, a roof with solar thermal collectors or photovoltaic modules. Green roofs are also referred to as eco-roofs, oikosteges, vegetated roofs, living roofs, and green roofs.

ABOUT GREEN ROOFING SYSTEMS

A green roof involves a high quality water proofing system that is root repellant. It must include a drainage system that includes a filter to keep the dirt from clogging it and lightweight to medium plants. There are a host of grant that will cover some of the cost of installing a green roof. Green roof systems are not popular in the US, however are popular in Europe with much support for there development by both government and private support. This is a multi-million dollar business in countries like Germany and France.  If your Association would like help planning for a green roof or finding funding for your project give us a call.

A green roof system if properly installed will not only provide a return on the investment, but will also provide social and environmental benefits especially in cities. Listed below are some of the benefits of a green roof:

Economic Benefits

Cost savings opportunities for the building owner include

  1. Protection of roof membrane resulting in a longer material lifespan (it is estimated that green roofs will last up to twice as long as conventional roofs), resulting in decreased maintenance and savings in replacement costs
  2. Savings on energy heating and cooling costs, depending on the size of the building, climate and type of green roof. Using a Micro Axess Simulation model, Environment Canada found that a typical one storey building with a grass roof and 10 cm (3.9 inches) of growing medium would result in a 25% reduction in summer cooling needs.  Field experiments by Karen Liu in Ottawa Canada, found that a 6 inch extensive green roof reduced heat gains by 95% and heat losses by 26% compared to a reference roof.

Some of the unseen energy savings from installing a green roof are listed below

  1. Potential to reduce the size of HVAC equipment on new or retrofitted buildings.
  2. Potential to reduce the amount of standard insulation used.
  3. Potential to incorporate cooling and/or water treatment functions.
  4. Provide a safe play area for residents and there children.
  5. Food Production – acceptable growing mediums are herbs, flowers and vegetables.  A community garden for the members could reduce food cost for the members.

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