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Greenroofs.com Publisher Linda Velazquez wrote an in-depth two-part article for Environmental Quality Management for the Summer and Autumn 2005 journal regarding the greenroof concept - see the descriptions below and download the PDF's to read more.

Organic Greenroof Architecture: Sustainable Design for the New Millennium
Environmental Quality Management, Volume 14, Issue 4, (subscription)

by Linda S. Velazquez
Summer 2005

"This article presents an overview of the greenroof concept. Included is discussion of the history of greenroofs -- which, though relatively modern in their present form, are rooted in ancient vernacular architecture and in the innate human desire to connect the built environment with nature.

I discuss basic greenroof technologies, and explain some of the key ecological, economic, aesthetic, and psychological advantages that greenroofs offer to both users and owners.


High-performance buildings, green design practices, and sustainable technologies are becoming increasingly important influences on architectural practices around the world.  They are even beginning to influence standards within the construction industry..."       >>more

 

Organic Greenroof Architecture: Design Considerations and System Components -
Growing a new roof - sustainably

Environmental Quality Management, Volume 15, Issue 1, (subscription)

by Linda S. Velazquez
Autumn 2005

"In the summer 2005 issue of this journal, I introduced the concept of greenroofs -- vegetated covers installed atop roof decks. I described some basic greenroof technologies, and explained some of the key environmental, economic, aesthetic, and psychological advantages that greenroofs offer.

In this article, I discuss the design of greenroofs, with details on system components, maintenance, cost issues, and the range possible applications. I also offer some thoughts on the future of greenroof development.


Greenroof Design: General Considerations

The greenroof design process is truly site specific, and requires open communication between the building owner and the design team..."    >>more


Continue to read below from the original 1999 website content:

Extensive Greenroof by Optima/Optigrun

Sindelfingen, Germany, Bank Greenroof by Peter Philippi; Source: Roofscapes, Inc., www.roofmeadow.com

The greenroof concept is akin to the popular, but traditionally heavy and difficult to maintain, garden roofs found atop buildings worldwide. Greenroofs are the result of a complete underlying roof build-up system, providing continuous, uninterrupted layers of protection and drainage.  Free drainage covers the entire roof surface, avoiding problems associated with walls and pillars built off a roof deck (ZinCo, 1998).  Recent strides in technology have advanced the properties of both extensive and intensive greenroofs, making them lighter, more durable and better able to withstand the extreme climatic conditions of the rooftop (William McDonough + Partners, 1999).  

Greenroof technology requires an appreciation and detailed knowledge of plant biology, hydraulic engineering and architecture. These are thoroughly engineered systems which address all the critical aspects of design, including:  the saturated weight of the system and load bearing capacity of the underlying roof deck; moisture and root penetration resistance of the waterproofing membrane; resistance to wind shear; management of drainage; and the suitability of the proposed plant material (www.roofmeadow.com).

Greenroofs don't have to be green!

Source: Optigrün international AG, www.optigruen.de 

The most important factor relating to any roof, whether it is a greenroof or not, is its long-term waterproofing function.  The ultimate priority of a greenroof is to keep the building watertight (Erisco-Bauder Ltd. Product literature, 1999).  Specifically, greenroof systems contain several layers of protective materials to convey water away from the roof deck.

Starting from the bottom up, a waterproof membrane is installed, followed by a root barrier, a layer of insulation (optional), a drainage layer, a filter fabric for fine soils, the engineered growing medium or soil substrate, and the plant material.  Usually some form of a biodegradable erosion  or "wind blanket," such as a jute or coco liner-type mesh, is placed over the new plants to stabilize establishing roots.  Roofs with a slope of 20º or more require steps to prevent shearing and erosion, and it is usually necessary to install additional support with cross battens (ZinCo's "The Green Roof Planning Guide").  A raised grid structure is then installed on these higher slopes to secure the growing substrate.  A shallow layer of gravel or pebbles are placed from 18" to three feet within the outside perimeter of the roof, providing additional drainage, fire control, and access to the roof for maintenance.  Vegetation selection is crucial to the long term success of the project, but by no means do greenroofs need to be green only to be an ecologically friendly building practice, as you can see by the above extensive red and yellow sedum greenroof by Optigrün.

The two basic types of roof greening covers are extensive and intensive greenroofs, with landscaped underground parking garages and earth-sheltered buildings offering similar properties.  

Rock Waterfall on Intensive Greenroof by ZinCo

Source: ZinCo International 3/98 Brochure

Differences lie in the desired function of the roof space, resulting in designs requiring different soil depths to accommodate various plants, shrubs and trees, and some additional structural support when necessary to accommodate higher live roof loads. Greenroofs can be warranted for up to 20 years.  Plant materials are usually warranted for one growing season, and benefit from supplemental irrigation and fertilization while getting established during the first year. Due to the return of organic matter to the soil, additional fertilization is not usually necessary.

The superimposed load resulting from a landscaped roof must be taken into account when accommodating the structural load.  The calculation must also be based on its saturated state.  Since 1995, the German professional association FLL - Forschungsgesellschaft Landschaftsbau Landschaftsentwicklung e.V. (The Landscaping and Landscape Development and Research Society) has highly researched various areas concerning greenroof design, including Design Loads in their Guidelines for the Planning, Execution and Upkeep of Green-Roof Sites (English Release, 2002).

The American Society for the Testing of Materials (ASTM) Green Roof Task Force passed the following ASTM standard regarding dead and live loads:

E2397-05 Standard Practice for Determination of Dead Loads and Live Loads associated with Green Roof Systems

Stay on top of things by reading the ASTM Updates column by Ralph Velasquez here.

Below is a chart from the ZinCo International 3/98 Brochure calculated in accordance with "German National Standard DIN 1055 - Design Load for Buildings" showing examples of roof covers and their approximate saturated weights for comparison:

Gravel Surface 90 - 150 kg/m2
Paving Slabs 160 - 220 kg/m2
Vehicle Surface From  500 kg/m2
Extensive Greenroof 60 - 150 kg/m2
Intensive Greenroof 200 - 500 kg/m2

 

Extensive Greenroof on the Ortho Dental Lab in Germany by ZinCo

Source: ZinCo International 3/98 Brochure

 

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