Minifie Park Green Roof

Location:                    290 Belmore Road, Balwyn, Victoria

Completion date:     December 2012

Area:                           440 m2 on a new building

Description

The roof is on a one-storey building in a park. There is no public access but the roof slope of 2 to 3 degrees means it can be viewed from ground level. The green roof includes a range of indigenous plant species to promote the use of local flora and provide habitat opportunities for fauna.

Introduction

Minifie Park Early Learning Centre is a council-owned, community-operated childcare centre located in North Balwyn, an eastern suburb of Melbourne. It was built to replace an older building.

Council decided to include a green roof as an integral part of the new facility. The purpose of the green roof was to provide thermal insulation and help the building blend in to the surrounding parkland.

The project received funding from Melbourne Water and the Victorian Adaptation and Sustainability Partnership to support the incorporation of water sensitive urban design features into the building.

The building was designed by the architectural firm FMSA and built by Behmer and Wright. The green roof was designed and constructed by Junglefy.

Design and components

The roof has a weight loading of 170 kg/m2. A gutter guard has been installed in the box drains, and leaf traps in downpipes to prevent them from blockage by pine needles from an overhanging tree. There is 400 mm wide unplanted perimeter zone to keep the areas around drains clear of vegetation.

Kalzip® aluminium standing seam roof sheeting was used for the roof deck. It was installed over a steel-framed portal structure – a building frame with pitched rafters. The standing seam system was a key element in Junglefy’s tender for the work, because its successful use on green roofs is well documented, and Kalzip was prepared to provide a 10-year warranty on the waterproofing. This is the first Australian green roof installed over this type of lightweight roofing system to Junglefy’s knowledge. The Kalzip® roof system is intrinsically watertight so a waterproofing layer or protection layers were not installed. 

The drainage layer was ZinCo FD40, with water-retention capacity. A ZinCo Filter Sheet SF was also installed.

The growing substrate was Junglefy’s proprietary Victorian mineral mix. It was delivered in 5,000 kg capacity bags, lifted by crane and installed through a hose attachment, and applied 100 mm deep. The large single substrate bag could be moved around the roof and greatly reduced the installation time compared to using multiple smaller bags. The substrate was covered with a layer of jute netting to provide weed control and protection from slipping due to gravity and wind forces. Plants were installed through cuts made in the netting. A layer of substrate was installed over the top to reduce the potential for wind uplift.

The Early Learning Centre has an additional bare roof area of approximately 300 m2. The green roof is irrigated with water collected over all roofs. Captured water is stored in an interconnected network of six tanks, with a total capacity of 24,000 litres, in the ground level plant room at the lowest point of the building. The modular tank system offers adaptability for current and future use: one or more tanks can be removed for repair or replacement without any need to interfere with the building structure and surrounds.

The irrigation system has ‘back to base’ control with sensor-driven monitoring from an inbuilt weather station enabling irrigation cycles to be missed during rain events exceeding a specified threshold. The system used is standard for parks and gardens irrigation throughout Boroondara. Water is pumped up to the roof from ground level and delivered to the plants through a KISSS Below Flow Flat capillary irrigation system. Initially, irrigation delivery was patchy across the roof causing uneven plant performance and the loss of a small number of plants, but adjustments to the system have resolved this issue.

The plant palette was a mix of low-growing Victorian perennial grass and herb species typically found in grassy/creek-line woodland (the likely original vegetation on this site). The herbs flower in spring and autumn, providing colour interest through a significant part of the year. Proposed additions include the planting of taller grasses to conceal the ventilation shafts.

Junglefy’s custom-designed aluminium edge restraints separated vegetated and non-vegetated areas of the roof.

Planting stock was contract-grown by Australian Ecosystems, provided as tubestock, and inspected at the nursery prior to delivery. Planting took place in November, after a delay, as a result, hand-watering was necessary over summer, to ensure the plants were well established.

 

Species

Austrodanthonia racemosa

Slender Wallaby Grass

Austrodanthonia setacea

Bristly Wallaby Grass

Poa morrisii Velvet

Tussock Grass

Themeda australis

Kangaroo Grass

Bulbine bulbosa

Bulbine Lily

Chrysocephalum apiculatum

Common Everlasting

Chrysocephalum semipapposum

Clustered Everlasting

Dianella revoluta

Black-anther

Flax Lily

Einadia nutans

Nodding Saltbush

Linum marginale

Native Flax

 

Maintenance

Junglefy has maintained the roof since planting. The intention had been that roof management would move to the City of Boroondara. However, due to Junglefy’s experienced management and competency to work at heights, they have been sub-contracted by the City’s Parks and Gardens team, and continue to maintain the green roof on a monthly basis. This arrangement has simplified management for the City of Boroondara.

The potential for acidification of the growing medium from the needles shed by a nearby overhanging pine tree is a source for concern.

Performance evaluation of the green roof plantings is being undertaken by the City of Boroondara.

Plant nutrition is provided as eight to nine-month low phosphorus controlled-release fertiliser applied at half the recommended rate.

Cost

Total: $306,000.

This included:

  • Design and preliminaries                    $180,000
  • Green roof installation and plants       $126,000

The total building cost was $3.5M.

Results and reflections

Insulation properties were a major driver for the inclusion of a green roof in the building design. An anecdotal story from builder Behmer and Wright’s site manager suggests that the green roof contributes to thermal comfort for users: after the green roof substrate was installed in winter, the builders elected to spend their lunchtimes in the facility as they found it was warmer than the site office. Monitoring of energy consumption for heating and cooling will reveal whether usage is lower than would be predicted for a building of this type without a green roof.

The City of Boroondara and the users of the Minifie Park Early Learning Centre feel very proud of the redevelopment and its green roof. The positive experience at Minifie Park has made Council enthusiastic to pursue future green roof projects. Council says that the local community has responded well to the green roof, seeing the views of vegetation as far superior to a bare metal roof. The design objective to create a connected visual experience between the building and the park has been met. The green roof demonstrates that a modern building development can be sympathetic to its surroundings.