Green Roofing
"living roofs"


By definition green roofing (most commonly referred to as living roofs) is the use of
increased natural / replenishable resources to protect and insulate structures.  In
essence living roofs have been around for hundreds of years.  Structures throughout
history have been insulated by soil and organics i.e. straw, vines, etc.  Within the
period of the industrial revolution, green roofing was widely discarded as petroleum
based roofing products took precedence.  In recent years, given the heightened
awareness of the global ecological situation, the idea of living roofs has been re-
developed and has begun to make its impact
on various regions around the globe.

Living Roofs are generally categorized as two types:

Extensive:  Low profile growing medium, typically two to six inches; little or no
irrigation; extensive roofs are generally installed for the sound and temperature
insulation qualities; vegetation includes: sedums, mosses, wild flowers, etc;
low maint.

Intensive:  High profile growing medium six inches or more:
can be designed to sustain shrubs & trees; complete irrigation system; vast plant
diversity; excellent insulation; accessible to people; higher maint. demands.



A living roof consists of six layers:


1.        Vegetation:  Consisting of a variety of carefully selected plants, grasses, etc.
specific to local weather / climate conditions.

2.        Growing medium:  Light weight, drainage friendly, mineral-based soil mixture.  

3.        Drainage:  A two part layer. First a filter layer: allowing water, but not the fine
materials of the substrate, to pass through.  Then: a layer of gravel or perforated
plastic sheeting, allowing excess water to flow to roof drains.  

4.        Insulation (optional):  Some extensive roof designs incorporate an extra
layer of lightweight substrate for added insulation or to prevent
loss of vegetation due to frost.

5.        Membrane protection / Root barrier (as needed):  Made of dense material to
inhibit root penetration and protect waterproofing layer.

6.       Roofing membrane:  The waterproof layer between the structure
and the living roof system.   

Note:        Due to the added weight of a living roof, structural
reinforcement may be necessary.


Each project is unique. The specifics of each layer should be discussed with
knowledgeable professionals to determine the appropriate specifications
and layering of living roof components before each installation.



Functions of Living Roofs


A.        Social benefits:  While extensive living roofs are not designed to accommodate
personal access, they can be designed to be aesthetically pleasing.  
However; intensive living roofs can support many functions. These include flower
and vegetable gardens, an outdoor oasis or  even golf courses.  Intensive living roofs
can be custom tailored to the specific wants or needs of the owner.



B.     Ecological:  There are numerous advantages to living roofs on an ecological
level. Living roofs provide important vegetated surface area in our cities.  This added
vegetation helps: naturally clean the air that we breathe through photosynthesis,
reduce the Urban Heat Island Effect (which can raise temps. in urban areas by as
much as 10-15 degrees), and can increase the real estate value
of any structure or neighborhood.  


C.        Economical:  living roofs have shown to substantially reduce the cost of
heating and cooling due to the excellent insulation provided by the substrate used.  
Green Roofs capture and use rain water, which greatly reduces the amount of runoff
water needing to be dealt with by existing sewer systems.  The life span of a Green
Roof is over twice that of a conventional roof.  This is mainly because there is no
“wear and tear” on the roofing membranes.  Damaged plants can be replaced at
minimal cost while the waterproofing layers remain protected from the elements.  With
traditional roofing, replacing the roof creates a large amount of waste.  In most cases
involving living roofs, the waterproofing layers can be repaired / replaced while the
upper layers of the green roof are preserved and re-used.

Living roof systems can also utilize rainwater harvesting systems to store
and reuse excess water that has filtered and drained from the living roof.  
Extensive Green Roofing systems, if designed properly, can also be paired with
Photovoltaics.
Sonoma County Rooftop Resource Inc.