A greenroof is simply a building with a cover of live plants as opposed to traditional roofing.  Typically there is a waterproof membrane and then soil or other growing media.  It may also be vegtative mats or modules linked together to form a living rooftop.  There are many advantages to constructing  a greenroof.  These include:   

• Reduction in both the heating and cooling needs for a building.
• Lessening the amount of stormwater runoff.
• Reduction of the urban 'heat island' effect.
• Filtration of air and water of pollutants.
• Adding new habitats for beneficial insects and birds.
• Increasing the lifespan of the roof.
• Use of the rooftop as an amenity to building occupants.

To learn more about greenroofs, you can go to one of these sites:

www.greenroofs.com    

www.xeroflora.com

Greenroof resources for Portland, OR