California Academy of the Sciences

Green roof technology is becoming very popular as a component for sustainable design.  Also known as a living roof, this new roof construction has achieved much value in LEED and NAHB green certification scoring and is more recently gaining popularity in city ordinances for new construction.  As green roofs in new construction projects increase in popularity it is important to know what a green roof is, the purpose of a green roof, and what is involved in constructing a green roof.

Green roofs are very identifiable compared to traditional roofing construction.  They can be pitched roofs but are primarily flat roofs that are planted with vegetation in a bed of soil that sits on top of the roof of a building. 

This design principle will increasingly appear in large city buildings and skyscrapers that contribute to the greenhouse gas effect and ozone depletion.  Buildings are responsible for half of all CO2 emissions.  For these reasons, it is environmentally responsible to build green roofs in order to convert some of this CO2 back into oxygen.  

Aesthetically, a green roof can add landscaped characteristics to an urban building that is minimally landscaped with potted trees on the sidewalk in front of it.  These plants on the roof can also hide mechanical systems that often visibly sit on roofs against an architect’s desire. 

Stormwater management is another sustainable asset to green roofing.  Stormwater runoff from melting snow and rainfall is becoming an increasing threat to natural water supply as impervious infrastructure continues to develop.  The problem is this runoff causes erosion, and transfers pollution, destroying habitats as it encounters waterways in increased volumes.  A green roof essentially covers the impervious surface it created with pervious surface by providing vegetation on the roof.  The EPA has done studies proving that the green roof absorbs this water and reduces run off by 50% compared to a traditional asphalt roof.   Green roof also performs as a filter for the water that does run off and lowers the peak flow rate.    

There are two types of green roofs; extensive and intensive.

 Extensive green roofs

· Carry 50-150mm of soil

· Lightweight, easy to design/install

· Self sustaining plants (no irrigation or maintenance needed)

· Only type of green roof possible for sloped roofs

· Plants used: moss, sedum, herbs, grasses

Intensive green roofs

· Carry 150-1500mm of soil

· Can handle a wide range of plants and trees

· Considered roof gardens

· Need regular maintenance and irrigation

· Substantial insulation properties

· Built on flat roofs only

California Academy of the Sciences - green roof construction