Design objectives

The fundamental reason for undertaking a green roof, wall or facade project needs to be identified up front, as this will influence the design, construction and required level of maintenance for the system. When building a green roof, wall or facade on behalf of someone else it is crucial thaflowers on green rooft the client’s requirements are understood. For example, a green roof designed for the purpose of increasing aesthetic value might focus on species of ornamental significance more so than drought tolerance or low maintenance. However, the same design might not be suitable for a client who wants a low maintenance, water efficient installation.

 

It should be noted that green roofs, walls and facades will be part of a broader urban green landscape and their design should ideally ensure that they contribute to the goals for the surrounding landscape, along with street trees and other forms of ‘green infrastructure’.

 

The following tables provide some examples of different considerations needed for different design goals. This is not an exhaustive list, and it has some very simple considerations: it is intended only to illustrate that different goals will require different inputs and system set-ups. Discussions with professional green roof, wall and facade installers, landscape architects and a review of relevant research will be needed to make final decisions about the most appropriate approach.

Green roofs

Design goals

Considerations

Reduced stormwater run-off

Increase depth and water-holding capacity of substrate, use plants with high water uptake

Recreation and amenity use

Increase weight loading, ensure ready roof access, planning and safety requirements

Lightweight, long-life and no irrigation

Choose stable, lightweight substrates and components, and high stress tolerant plants, e.g. succulents

Cooling and integration with photovoltaic panels

Select leafy plants, provide irrigation, plant around (but do not shade) solar panels

Maximise thermal insulation

Increase substrate depth, provide irrigation, select species for leafy plant cover in summer (passive heat gain in winter may be increased if the roof is bare in winter but this strategy increases maintenance and reduces aesthetic benefit)

Provide biodiversity outcomes

Include habitat plants (usually native/indigenous), habitat features (such as water and shelter), small changes in topography and variations in substrates.

Produce food

Increase weight loading capacity of the roof, and depth and organic content of substrate, ensure good access to the site, provide irrigation

Green walls

Design goals

Considerations

A multi-storey green wall

Ensure access for maintenance is possible, consider hydroponic system if weight loading is likely to be a problem, ensure species selection is appropriate for the specific light and wind exposures at different heights

Aesthetics and a design statement on a building

Include a variety of species with different flowering times, consider planting in patterns and consider textures, foliage colours and extending the planting area beyond the boundaries of the green wall surround

Low cost and easy to install on a residential building

Consider DIY installations, minimise the size of the system, self-contained units that recirculate water, systems that can be easily replanted

Provide biodiversity outcomes

Include a variety of species with habitat features such as fruits or nectar-producing flowers, or a niche design that provides protection from predators for particular species

Internal green wall

Ensure adequate light – possibly install artificial light

Long lasting wall

Consider quality of design and longevity of components

 

Green facades

Design goals

Considerations

Low cost and easy to install

Use a direct attaching species of plant, grown from the ground at the base of the wall

A multi-storey facade greening

Include containers at different heights, include cabling or lattice support structures for twining plants, ensure access for maintenance, provide irrigation, consider secondary protection of plants against stem damage, e.g. wind protection trellis

Screening of an unsightly view

Use evergreen species to ensure year-round screening, create a structure for the plants to grow on

Maximise thermal benefits

Use deciduous species if heat gain is desired in winter; ensure very leafy plants, covering the entire wall for providing best shade in summer, particularly on north and west facing walls; provide a structure at least 100 mm off the wall of a building for the plants to grow on, leaving an air gap between the building and green plants to maximise cooling effect.

Produce food

Increase depth and organic content of the substrate, ensure good access to the site, provide irrigation

Provide biodiversity outcomes

Include a variety of species, with habitat features such as nectar producing flowers, fruits, capacity to support nests, create protected or visually prominent areas