1. What is a Green Roof?
2. What are the different types of Green Roof?
3. How much does it weigh?
4. Do I need to water it?
5. Are they always green?
6. Where can I see an existing green roof?
7. Do leaks and other problems occur?
8. Can people walk on the green roof?
9. Can I put a green roof on my existing residence?
10. Does the roof have to be flat?
11. Are there proven, scientific standards for green roof design?
12. Do you use the same system on all roofs?
13. How are the plants installed?
14. Could I use NZ natives?
15. What are the rates of coverage for each system?
16. Can you give me an idea of cost?
17. How often does maintenance need to be carried out?
18. Why would I want a green roof?
19. Do I need Council permission for a Green Roof?
20. Could a green roof contribute additional points towards a Green Star NZ rating for a building?
1. What is a Green Roof?
Roofs that are either partially or completely covered with plants are considered green roofs. While green roof technology is somewhat new in NZ, European countries, in particular Germany, have been designing green roofs for decades. Each particular green roof varies, however, every green roof contains the following basic components: waterproofing membrane, root barrier, drainage and water retention layer, growing medium (substrate) and plants.
2. What are the different types of Green Roof?
Green roofs are classified as either extensive or intensive. Extensive green roofs are lightweight and low maintenance. They are usually inaccessible and are therefore planted with drought-resistant species, which survive on rainwater. Intensive green roofs require comprehensive maintenance. Because intensive green roofs are often accessible and more elaborately planted, buildings must be able to bear extra weight. Issues of irrigation, fertilisation, pest control, and plant selection are also more complex.
3. How much does it weigh?
The maximum weight of a fully saturated sedum mat roof in 25mm substrate (i.e.
all the material above the waterproof layer) is 100 kg per square metre. An intensive green roof could weigh as much as 200 kg per square metre.
4. Do I need to water it?
Not always. A sedum roof installed during summer would benefit from occasional watering
to become established. Regular irrigation would more likely be needed for a
more intensive roof or one using NZ native species.
5. Are they always green?
No! Many greenroofs appear red, orange, yellow and all colours in between at
different times of the year because the fleshy leaves of various succulents
change colours throughout the year. Also, greenroof plants are not all evergreen,
nor should they be. The beauty and anticipation of the change of seasons add
to the colour palette. And of course, flowers vary, too, in colours from whites
to yellow, pinks, deep reds and purples and blues. A virtual living carpet or
tapestry varies from season to season as plant communities naturally migrate
in their random regenerative patterns
6. Where can I see an existing green roof?
Greenroofs Ltd have worked on the Waitakere
Civic Centre green roof in Henderson, University
of Auckland’s green roof trials at the School of Engineering and have
completed a demonstration project at the Sustainable
Living Centre in New Lynn. In addition there are many other existing green
roofs such as the Hundertwasser toilets in Kawakawa or Muriwai public toilets.
7. Do leaks and other problems occur?
Greenroofs protect the waterproofing from ultra-violet radiation and thermal
shock. These are the two main elements that age and eventually cause the waterproofing
to fail. It is generally accepted that installing a green roof will double the
estimated life expectancy of a newly installed waterproofing system. It is essential to ensure that the waterproofing has been flood tested and signed off before the green roof is installed. A green roof will not cause a roof to leak as long as it has been installed correctly by someone who knows what they are doing.
8. Can people walk on the green roof?
Generally, extensive green roofs are not designed for pedestrian traffic. But
the occasional incursion by an inspector or maintenance worker would not be
a problem for most commonly used plants.
9. Can I put a green roof on my existing residence?
Many people have realised the benefits of a green roof on their own home. For
either existing dwellings or new construction, a structural engineer should always be consulted to determine the structural requirements of a green roof. For smaller roof areas of 50m2 and less Greenroofs Ltd now provide a DIY kit. Please see Our Products and Services for more information.
10. Does the roof have to be flat?
No the plants and substrate will be stable and successful at pitches up to 30
degrees.There are ways to green a roof above this pitch but they can make it more expensive.
11. Are there proven, scientific standards for green roof design?
Presently, the only widely accepted, established standards for green roof construction
are those developed in Germany by the the Forschungsgesellschaft Landschaftsentwicklung Landschaftsbau (FLL).
These standards and guidelines are comprehensive, and include industry standard
tests for the weight, moisture, nutrient content, and grain-size distribution
of growing media. FLL also certifies laboratories to conduct critical tests,
such as the root penetration resistance of waterproofing membranes. These guidelines
are available in English translation.
12. Do you use the same system on all roofs?
No. The design of each system with regard to build up and plant selection will vary for each roof. As well as client requirements and budget, factors taken into account include building location, surrounding environment, orientation of the roof and localised microclimates on the roof.
13. How are the plants installed?
The type of plant installation used depends on site conditions, plant selection, rates of coverage required and budget.
Option 1 is plug planting – young plants are manually installed into the substrate/growing medium at the given density and the roof plant layer establishes over time.
Option 2 is the Greenroofs Ltd mat system – the plant layer is field grown to maturity,
rolled up and transported to the prepared roof to be installed as an instant
mature plant layer.
14. Could I use NZ natives?
Yes there are many NZ species suitable for roof planting. However the substrate/growing medium needs to be deeper than for sedum and they may require more maintenance.
15. What are the rates of coverage for each system?
A plug planted roof will achieve 80% plant coverage 9-12 months after installation. A mat system gives instant plant coverage of over 90%.
16. Can you give me an idea of cost?
Based on a large roof over 200 metres square and not including craneage, delivery, edge details,
GST or travel costs a sedum plug roof can cost from as little as $150 per sq m (20 plugs per sq m), NZ native plugs from $215 to $280 per sq m and sedum mat from $200 per sq m.
17. How often does maintenance need to be carried out?
Generally, 4-6 visits in the first year. 1-2 visits for subsequent years.
18. Why would I want a green roof?
- Extend the life of the roof.
- Reduce storm water run-off
- Improve thermal performance of the roof.
- Improve habitat for birds and insects.
- Absorb carbon dioxide and reduce greenhouse gases.
- Improve acoustic performance.
- Aesthetics - they look good!
19. Do I need Council permission for a Green Roof?
The simple answer is yes, at this stage. You will, at the very least, require a building consent for the green roof. Depending on what zone you live in, you may require resource consent. It's really a case-by-case issue so it would be wise to approach your local Council to check. Not obtaining the appropriate approvals early on can complicate things in the future.
20. Could a green roof contribute additional points towards a Green Star NZ rating for a building?
Yes. Under the Ecology calculator, Emissions (Watercourse pollution) and possibly under the Energy calculator a green roof could earn additional points for a project. The emphasis is on the project team to prove that the installation of a green roof meets the credit criteria as laid out within the Green Star NZ rating tools. Additional points could also be awarded under the Education Design and Built 2009 tool under the Management category for the Learning Resources credits. Please see www.nzgbc.org.nz or contact one of the Greenroofs Ltd team for more information.