Freshwater Place Green Roof

Location:                     1 Queensbridge Square, Southbank, Victoria

Completion date:      2004

Area:                           1,650 m2 on anew building

Description

The green roof is an elevated landscape located on top of the nine-storey car park. It is made up of a series of garden mounds, a grass lawn, storage sheds and planter boxes for growing vegetables. A windbreak wall was added to protect the site from the strong southerly wind.

Introduction

Freshwater Place is a residential complex containing 534 apartments, located on the Southbank side of Melbourne’s Yarra River. The aim of the project was to provide residents with a functional outdoor space that would enhance their inner-city lifestyle and add value to the property. The green roof is part of the communal facilities, which include barbeque areas, pool, gym and function spaces. Residents and their guests have full access to the level 10 roof and it can be seen from most of the apartments as they extend many floors higher than the car park. Maintaining the green roof’s aesthetic appeal is the priority for all maintenance activities. 

The green roof was a collaborative project between Bates Smart Architects, Australand and Laurence Blyton Landscape Architects. The green roof components were installed by Fytogreen and are maintained by Facility Management Victoria.

Design and components

The roof was installed using the following layers: 

  • waterproofing spray-on layer, installed by JA Dodds
  • waterproofing protection layer, low-density polyethylene (LDPE) foam
  • Flo-Cell™ drainage layer
  • Bidim® geotextile layer
  • Fytogreen Hydrofoam hard foam RG30
  • growing substrate

Vegetable planter boxes, provided by the Little Veggie Patch Co, are made from recycled apple crates. Measuring 1.2 m along each side, and about 80 cm tall, the boxes are anticipated to last more than 10 years. The vegetable crates are located on the west side of the site and receive less sunlight than the other sections of the roof.

There are 30 established trees growing in the green roof garden beds, surrounded by a range of shorter shrubs. The substrate in these beds is 70 cm deep to accommodate the trees’ root systems. Comparatively, the substrate under the large lawn area is only 35 cm deep. The substrate mix used throughout the site was prescribed by Fytogreen, and is made up of sand, organic material and water retention flakes. A river stone mulch layer sits on top of the substrate to reduce evaporation, reduce weed growth and stabilise the soil in the wind.

There is a mix of permanent green elements, seasonal interest from foliage and colourful flowers. There is also one lemon tree on the roof, after a request by a resident that it be planted. It is yet to fruit, but is growing well.

Replacement species have been selected from existing plants that have grown well.

The specific plant species used on the Freshwater Place green roof are listed in the table below. All species are low maintenance, can be grown in most climates and soils, are tolerant of drought and wind, and prefer to be grown in full sun to part shade. They can be grown in urban areas where pollution levels may be high.  

Plant species used

Pyrus ussuriensis

Manchurian Pear cultivar

Dianella

‘Little Jess’

Juniperus sabina

Savin Juniper

Liriope cultivars

Lily Turf

Viola hederacea

Native Violet

Viola labradorica

Labrador Violet

Ixia cultivars

Corn Lily

Escallonia cultivars

Ipheion uniflorum

Spring Star

Freesia cultivars

Iris cultivars

Rahiolepis umbellata

Yeddo Hawthorn

Pennisetum clandestinum

Kikuyu

Trachelospermum jasminoides

Star Jasmine

 The green roof drains into a 160,000-litre storage tank that sits beneath the paved area. Rainwater is also collected into this tank from other building surfaces. The collected water is used for irrigating the garden and can sustain the plants for up to three weeks in the height of summer, and as a result, potable water is rarely used.

A drip irrigation system was installed beneath the substrate in the garden beds as part of the initial construction, but this system is no longer used. Although it was functioning correctly, the system did not allow for the different water requirements of trees and other plants. In 2010, the maintenance team installed separate drip irrigation systems for the trees and shrubs, which run along the surface of the soil. The grass lawn is watered using automated sprinklers.

The plants are monitored daily to ensure that the irrigation is sufficient and to identify problems before the plants showed signs of distress.

In the initial design, five round plant rooms on the roof were topped with vegetation to provide residents in the apartments above with a consistent green outlook onto the green roof. Sloped at a slight angle to allow for drainage, these roofs were planted with succulents in a shallow substrate made of fine stone aggregate. Parts of these roofs became waterlogged and caused some plants to fail, resulting in patchy green coverage when viewed from above (see image). Although the drainage could have been repaired and the roofs replanted, maintenance staff chose to not replace the plants, leaving the area with just the stones. This decision was made to ensure that the residents had a pleasing outlook onto the roof at all times. 

Maintenance

Although the green roof at Freshwater Place has been designed to minimise maintenance, there are ongoing challenges. A different level of maintenance is required for the intensive garden beds and the extensive lawn area. For an annual fee of $25,000, the maintenance is carried out under contract and includes replacement of plants. Maintenance activities include:

  • Irrigation:                                  Three times per week in summer; varies for the shrubs
                                                       and trees
  • Pruning:                                    Annually for trees; shrubs as required
  • Plant evaluation:                     Weekly
  • Lawn mowing  :                      Weekly in spring; fortnightly at other times
  • Scarifying the grass:              Every three years
  • Fertilising:                                Monthly for turf; plants every six months; annually for
                                                       trees 
  • Plant renewal:                         As required in winter
  • Cleaning and monitoring of
    hard landscape elements:   Weekly
  • Inspection of irrigation
    system function:                     Daily in summer; monthly at other times

 

A key challenge for maintaining the green roof has been ensuring that plants get enough water to maintain optimum growth and to look healthy and visually appealing. This requires regular monitoring, so it is important that the maintenance contractor understands the environment and how it can change very quickly.

Originally, Tall Fescue grass was used as lawn cover, but the maintenance team found it difficult to keep it looking good through water restrictions and the hot summer months. At times security staff hand-watered in summer to keep the grass green. Following a review of plant maintenance in 2007, the tall fescue was replaced with Kikuyu grass, a species with lower water requirements, and it has been very successful.

Exposure to the elements has also been a challenge, particularly for the maintenance of the large Manchurian Pear trees. The strong wind has caused them to grow at an angle, particularly in the older tree stock, due in part to the use of fully-grown trees at installation, As a consequence, the root systems did not establish in the soil as well as they could had younger plants been used. Their lack of stability in the wind required the use of support cables. Recently, some of these trees were replaced with younger plants and these have quickly grown to be equal in size to the existing trees, and are far more stable.

Maintenance processes are regularly reviewed to ensure they are consistent with the desired outcomes.

Results and reflections

Overall, the Freshwater Place management team is extremely happy with the aesthetic and social benefits of the green roof. The useability of the space gives the building a unique edge and adds value to the property.

The green roof is a well used space, particularly in the warmer months of the year. The barbeques are in constant use throughout the summer and the lawn is a popular place for picnics. The vegetable gardens are maintained by residents, who enjoy the social aspect of growing produce together.

Reflecting on the lessons learned over the last nine years, the management team has advice for anyone considering a green roof project:

  1. Green roofs have their own challenges due to the unusual nature of the site, so it is best to keep the design simple.
  2. Green roofs are not ‘set and forget’. It takes some time to get the plants, irrigation and maintenance right, so be prepared to make adjustments as you go along.
  3. Monitoring the green roof components and plants is essential for establishing a successful green roof. The monitoring should be regular and not reactive.