The Venny green roof
Location: JJ Holland Park, 85 Kensington Road, Kensington, Victoria
Completion date: September 2010 (remediation works July 2013)
Area: 108 m2 lower roof; 103 m2 upper roof on a new building
The Venny green roof comprises a lower flat roof, with planting designed around three sections – A, B, and C – and an upper, sloping green (roof D), a later addition to the original brief. The green roof can be viewed from the ground, access is only available for maintenance. The upper roof contains an array of photovoltaic cells (44m2), two solar hot water panels and a roof ventilator, leaving approximately 46m2 for planting.
The Venny is a community facility for children from the Melbourne suburb of Kensington and surrounding neighbourhoods. Design of The Venny was commissioned by the City of Melbourne, incorporating the use of recycled shipping containers. As protection was needed to insulate the spaces below the metal containers, a green roof was suggested as the most appropriate solution. It was also anticipated that the roof would expand the local knowledge of green roof design, installation and maintenance at a residential scale.
The project was a joint venture between the City of Melbourne, The University of Melbourne and Melbourne Water. The roof has also been a research site for The University of Melbourne, with funding provided through the Australian Research Council.
Detailed design of the lower areas was undertaken by The University of Melbourne and the upper green roof was designed by Junglefy Pty Ltd.
Design and components
A ZinCo system was used for the waterproofing and drainage components. A low cost membrane material, Volclay Swelltite®, was used. The lower green roof comprises a ZinCo system, including a 25 mm drainage cell, and two different mineral-based substrates developed by The University of Melbourne. The upper roof used an alternative system incorporating a basal protection layer with irrigation (capillary irrigation matting) and, originally, a 100 per cent coir media at 100 mm depth. Galaku erosion control netting was used to hold the plants in place on the upper roof.
Plants for the green roofs were researched and selected by The University of Melbourne, based around aesthetic properties, drought tolerance and low resource inputs (water, fertiliser and maintenance). Most were succulents, particularly sedums, aloes and related species. They were planted at high densities to provide rapid cover and discourage weed infestation.
The upper roof has been designed to hold a green roof with a saturated load of 160kg/m2 (including all plants, substrate, irrigation system and waterproofing). In addition to the 160kg/m2 there has been an additional live load allowance of 40kg/m2.
Management and maintenance was considered in the initial design, and a safe maintenance access point was important. A lockable alcove was designed with a purpose-built ladder and signage to comply with occupational health and safety standards. Paths of chipped recycled brick were incorporated into the initial design of the lower roof to minimise the impact of maintenance and research activities on plants and green roof infrastructure. These factors, combined with the specific species selection of drought tolerant plants and a close planting design, were considered to culminate in a green roof that could be safely managed, with low impact, and low maintenance requirements.
The first two years of maintenance and management was undertaken by The University of Melbourne, as part of its research studies, and Junglefy Pty Ltd. A comprehensive management plan was devised by The University of Melbourne and handed over to the City of Melbourne. This was the first green roof that the City of Melbourne’s landscape maintenance team had experienced and some problems did occur when the irrigation system failed over summer. The maintenance visits also became infrequent which meant that the health of some of the species was compromised. After approximately six months’ maintenance by the City of Melbourne the roof was evaluated and it was determined that while the lower green roof was satisfactory, the upper roof had not performed well. The coir growing media failed to support plants adequately – the only surviving species had drifted to the base of the roof slope. While disappointing, the substrate was used as a trial and the substrate and plant replacement was not an unexpected expense for the project.
Remediation of the upper green roof took place in July 2013. The University of Melbourne was contracted to develop a lightweight, mineral substrate and complete a planting design. Junglefy were re-engaged to take the lead in the remediation works – including the removal and replacement of the growing medium and the installation of new plants.
New ZinCo products, specifically designed for sloped roofs, were used, a ‘back to base’ alarm system for monitoring irrigation was installed, and Junglefy has continued ongoing maintenance of this space.
Lower Green Roof
Specific costs of project components:
- Shipping container steel frame Recycled
- Drain pipe system $5,000
- Bentonite liner $16,000
- Concrete screen $18,000
- ZinCo system (supply) $7,150
- ZinCo system (install) $1,360
- KISSS ‘Below Flow Flat’ irrigation
and associated controls $6,330
- Substrate growing medium and
crushed brick paths $5,900
- Coir mulch matting $1,270
- Plants (supply) $4,520
- Plants (install) $3,540
Upper Green Roof
Total cost: $11,000, including the waterproofing layer, growing substrate, irrigation, plants and planting, labour and materials.
Note: it would be unrealistic to expect to replicate such a build for the same price today. Junglefy’s involvement in construction was undertaken at cost due to its interest in developing this industry.
Remediation works in 2013 cost approximately $43,000.
Results and reflections
According to The Venny manager, the roof adds environmental, educational and economic benefits to the building. As a small-scale building the design could be applied in a residential context.
Lessons learned included that:
- the bentonite liner and concrete screed on the lower roof, expensive items which did not live up to expectation, would be avoided in future
- the use of 100 per cent coir as a substrate on the upper roof would be avoided (this was addressed in the remediation)
- the slope called for a water retention layer (this was added in the remediation in 2013).
The Venny has proven to be a pioneering project that has provided a valuable learning experience for the emerging green roof industry. Those involved in similar projects should invest in good materials for waterproofing and drainage, as well as consulting those with expertise in design and application to ensure plants are appropriate for the type of roof.
A consistent message in the reflections of The Venny green roof partners was that patience is required when undertaking something that is untested: it is a collaborative learning process through all stages from design through to management.