Waitakere Council Green Roof

This webpage provides guidance on how the Waitakere Central Civic Centre green roof was developed and contains all the technical information and associated links that might be of use to anyone investigating creating their own green roof.

Introduction

Construction and monitoring of the extensive green roof at the new Waitakere Central Civic Centre building in Henderson has been funded by Waitakere City Council to provide quantitative information to help overcome barriers to adoption of green roofs on buildings in New Zealand and to promote the use of native plant species on New Zealand green roofs.

The aim is to look down over the City in the future and see a proliferation of living roofs absorbing and slowly releasing stormwater - a network of vegetated stepping stones with native plants and insects reducing the heat and noise of the city.

Awards

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NZILA Resene Pride of Place Landscape Awards 2008

Gold award in landscape planning category for communication and promotion (Size 289K)

Sustainability Award of Excellence (Size 294K)

Green Roof Image Gallery

Photos of green roof during construction, September 2006 - November 2007, insects on the roof and green roof viewing area

Crane delivery of substrate to roof during construction	Substrate being unloaded onto roof	View of green roof September '06
View of green roof plants October '07	Green roof signage in viewing area	Green roof model showing layers
View of green roof November '07	View of green roof November '07	View of green roof November '07

What is a Green Roof?

Roof gardens, are not a new phenomenon, many have existed atop buildings for decades, however, such (intensive) roof gardens are expensive to build, and require a lot of modification of roofs to support the increased weights associated with soil and plants.

The new concept for green roofs is for (extensive) roof systems which involve providing a very thin layer of soil over the roof structure that supports low growing vegetation.

Extensive green roofs are the lightweight, modern versions of the sod roofs that are a centuries-old tradition in Scandinavia. Extensive roofs do not necessarily require flat roofs and can be installed on roofs with slopes of up to thirty degrees if provided with a raised grid structure to hold the growing medium in place. They are not intended to be walked upon and generally do not feature pedestrian access. In contrast to conventional roof gardens, that require irrigation systems, fertilisation and frequent maintenance, extensive green roofs require little or no irrigation or fertiliser.

Benefits of a Green Roof?

Green Roofs are a key Low Impact Urban Design technology that;

• Reduces the impact stormwater runoff in urban areas with high roof coverage - the roofs store rainfall, working like sponges to reduce and slow runoff into stormwater pipes, cumulatively helping lower downstream impacts of flooding, stream bank erosion, and stream degradation.
• Improves the building's thermal insulation and reduces the urban 'heat island' effect.
• The vegetation on green roofs filters city air, absorbing carbon dioxide and helping to reduce air pollution.
• Creates habitat for birds, butterflies and other insects.
• They have the capacity to absorb a percentage of the rain that fall on them, thereby reducing the runoff from impervious surfaces and alleviating potential flooding problems that plague many cities.
• And finally, they can look great by providing lush vegetated space on a hard building structure.

Waitakere City Council's Green Roof Vision

• To demonstrate the range of sustainabile benefits of green roof technology.
• To create a green roof which is specific to the New Zealand situation, and at least in part, reflective of plant species found in the Waitakere environment.
• To create an organic patchwork of plants which will move and change over the years with competition and natural growth styles.
• To provide splashes of colour variation through leaf colour, texture and seasonal flowering.
• To ensure a multitude of outcomes are achieved for stormwater, habitat and amenity.
• To provide a robust, well-researched and documented process for plant selection, including substrate make-up, and monitoring to provide useful and innovative input into green roof technology specific to New Zealand.

Features of the WCC Extensive Green Roof

click to enlarge

Extensive greenroofs have a drought-tolerant plant cover growing in lightweight, thin (50 to 150 mm deep) 'soil' on a drainage material and waterproof membrane.

The media used in greenroofs need to balance lightness with moisture retention and cost.

This drawing and model shows how the WCC green roof is constructed.

For more details on the substrate and materials we used on our green roof and for construction details

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Green Roof Construction Drawings (Size 808K)

Green Roof Information Pack (Size 7838K)
If you are not able to download a copy of the information, or would like a hard copy of the information pack, then please email Renee.Davies@waitakere.govt.nz with your name and postal address and we will send you a copy.

Our Green Roof Plants

Plant species chosen in the northern hemisphere for use on extensive green roofs have evolved from choosing the most drought tolerant plants.

Succulent Sedums have been chosen as they have grown naturally on roofs and walls with little substrate and are therefore adapted to extremes and lack of moisture.

Waitakere Cities aim was to find New Zealand native alternatives that will form a dense, weed-resistant cover and survive in these very droughty sites with little watering.

Ongoing Monitoring

Waitakere City Council is going to monitor how clean the the water run-off from the green roof is and compare that to a normal roof. We will also be monitoring the success of the native plants and the habitat value of the green roof. This information will confirm how much benefit there is to using a green roof in New Zealand. This information will then be available to others who might want to build a specifically New Zealand green roof.

Green Roof Diary

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How Do I Plan My Own Green Roof?

It's not just large or commercial buildings that can have an extensive green roof. There are opportunities to create green roofs on and around your own house and garden. Any area of flat or semi-flat space can be considered, such as garages, letter boxes, sheds, small extensions, verandahs.

The creation of an expansive green roof can be a way to address Council and Regional Council stormwater issues within a new development. The Auckland Regional Council provides some guidelines in relation to green roofs for stormwater management.

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The key things to look at when thinking about creating an extensive green roof include;

• The condition of the roof (. is it a new roof about to be constructed or are you proposing to retrofit an existing roof)?
• The structural capacity of the roof (ie. can the roof support the additional weight of the green roof and/or is it being designed to accommodate the additional weight)?
• Determine the weight of the green roof
• Determine the cost of the green roof
• Design of the green roof (ie. what materials will you use, what plants will you use and how will it be maintained)?

The information on this webpage may give you ideas and help you plan your own green roof. However, it is only a guide and cannot take the place of expert advice from relevant professionals such as structural engineers, architects, landscape architects and roofing contractors. If you are planning a green roof you will benefit from the advice of an expert.

Article on green roofs

The following article provides further information on green roofs and some New Zealand examples of existing green roofs.

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Potential nz plants for extensive green roofs (Size 2371K)

Sprouting green roofs in New Zealand (Size 1612K)

If you are interested in creating a small green roof the following document downloadable free from the Natural England website provides some useful guidance and considerations for your own back yard.

Living Roofs

Useful Resources on Green Roofs

Specialist Books on Green Roofs

Green Roofs: Ecological Design And Construction

Planting Green Roofs and Living Walls

Green Roof: A Case Study: Design by Michael Van Valkenburgh Associates for the Headquarters of American Society of Landscape Architects
by Christian Werthmann (Author)
Hardcover: 160 pages
Publisher: Princeton Architectural Press (July 26, 2007)
ISBN-10: 1568986858
ISBN-13: 978-1568986852

Links

www.greenroofs.net

www.greenroofs.co.nz

www.greenroofs.org

www.landcareresearch.co.nz

www.livingroofs.org

www.igra-world.com

Further Information

If you would like a hard copy of our Green Roof Information Pack sent to you, have any queries regarding the Green Roof or would like to arrange a visit to view our green roof please contact:

Renee Davies
Service Manager Parks Planning
09 836 8000 ext 8118
Renee.Davies@waitakere.govt.nz