FAQ

What are green roofs, walls and facades?

See the following pages for our definitions of green roofs, walls and facades.

Do green roofs work on new and old buildings?

Yes. Green roofs can be fitted to a range of roof types. A new building can be constructed to accommodate the weight loading necessary for a green roof. Some existing buildings will have the capacity to support a green roof, or additional structural support can be retrofitted to support the required increase in loading. A structural engineer must be engaged to clarify details of building structure and weight loading capacity.

Is there financial support available for building green roofs, walls and facades?

Currently, in Victoria, there are no funds specifically targeting green roofs, walls and facades.  There is however provision of finance for loans for building retrofit projects through the Sustainable Melbourne Fund. They can provide up to 100% loan finance for building retrofit projects or for innovative technology that delivers wider environmental benefits. They will boost or match private and public sector funding.  There are also many other programs for grants or other support through government and other sectors where these systems will also be eligible.

Can I green any building?

Most building surfaces have the potential for greening. Challenging sites such as those in deep shade or with low weight-loading capacity, and tall buildings or sites with limited access, require specialist engineering, design and technical input.

Can I have a green roof on a slope?

Yes, but steeper slopes present a challenge, and require specialised design solutions, including drainage boards and systems to help hold substrates and plants in place.

Can a tile roof be greened?

Yes, but it requires design expertise and specialised systems that are not yet widely available in Australia.

Is irrigation necessary for a green roof, wall or facade? 

All green walls and most green facades and roofs, require irrigation. It is possible to install a green roof with no irrigation, but this will limit the range of plants that can be used successfully and the potential benefits of the roof (such as summer cooling or aesthetically pleasing views of leafy plants). Some green facades grown in garden bed settings may not need irrigation.

How much water do you need?

There is no one answer, as calculating the water needed to sustain a green roof, wall or facade depends on climate and environmental influences, the design and type of system used, and on the substrate and vegetation characteristics. Explore alternative sources of water for use in irrigation, such as harvested and recycled water, to minimise reliance on potable water. Many green walls rely heavily on irrigation and it is essential to establish that supply can meet demand.

Will the green roof leak and cause problems?

Any roof has the potential to leak.Well-constructed green roofs, walls and facades will not leak or cause other structural damage to the building. Correct installation of waterproofing is essential on roofs and some walls, and leak detection systems can minimise risks on green roofs. Waterproofing membranes can actually last much longer under green roofs because they are protected from damage by the elements by overlying layers.

Will plants ‘overtake’ the roof or wall?  

Vegetation maintenance on a green roof is important and should be factored in during the design phase of the project. Selection of less vigorous plants (species with low biomass) or those that do not seed freely will help reduce maintenance requirements. Green walls can be designed to have an air gap between the back of the system and the wall, to provide air pruning of roots. Green facades will require pruning to manage size and maintain effective cover.

How much do green roofs, walls and facades cost?

Costs will vary significantly between sites and projects. The case studies in this guide indicate costs for a range of projects of varying complexity for comparative purposes. The key factors that influence costs are the size of the roof, wall or facade; the design and type of materials used in the roof (for example, structural reinforcement, volume of growing substrate and components used in the mix, plants, system components, hard surfaces and furniture, etc.); requirements for access; and the requirements for ongoing maintenance (including inputs for irrigation, weeding, pruning, fertiliser).

Green wall technologies offer notable variation in costs, with relatively cheap domestic green wall products suited to small-scale DIY (do-it-yourself) applications, through to large and small-scale custom-designed commercial systems. Each presents a different level of refinement and security for long-term success.

Can I have solar panels on a green roof? 

Yes. There are examples of green roofs in Melbourne and other parts of the world where green roofs have solar panels installed above them.

What’s the typical lifespan of a green roof, wall or façade?

The lifespan is directly related to the quality of the design, construction and maintenance, and in particular, the longevity of the system components. Some green roofs in Europe have been in place for more than 75 years and are still performing strongly. There are many examples of direct façade greening in Melbourne that have lasted for decades. The projected lifespan of green wall and facade technologies that are more recent entries into the market are less well understood.

Will construction of a green roof, wall or façade cause delays in the construction of my building?

Although a green roof, wall or facade should be considered an integral component of a building, its construction can usually be done independently from the rest of the build, so it poses little risk in causing delays. It is very important to include the installation specialists in early design discussions and associated construction project timelines to establish the most efficient construction timetable and ensure that drainage, irrigation and lighting are designed to include the green roof, wall or facade.

How do I know if my building has the capacity for a green roof?  

An architect, engineer and green roof provider are needed to ascertain that a green roof can be installed on a new building. To retrofit a green roof on an older building, consultation with an architect and/or structural engineer is necessary to determine the load-bearing capacity of the structure. Consult with green roof, wall or facade providers to discuss design ideas and solutions for the site.

Could I just paint my roof white to achieve summer cooling?

Increasing roof reflectance through a ‘white roof’ is one way of reducing heat gain through the roof. However, a white roof will not capture and retain stormwater, provide aesthetic benefits or increase biodiversity values. Paint eventually degrades and requires maintenance. Most white roofs cannot help insulate the building in the winter months and will therefore only improve the building’s energy efficiency in the heat but not the cold. A green roof can help a building’s energy efficiency year round.

How much pruning will be needed if I grow a green facade on my building walls?

Pruning is usually required once or twice a year, although this will depend on the vigour of the plant species and the growing conditions. Annual pruning is important to control growth and keep vegetation away from building fixtures (lighting, heating or cooling equipment, drains).

Are green roofs, walls and facades environmentally sustainable?

Design of the system is paramount to how well it contributes to broad sustainability goals, such as pollutant filtration, thermal insulation, providing habitat or localised cooling. By considering how you design, operate and maintain your system you can also ensure that the materials and practices used are environmentally sustainable now, and in the long term. This process is called ‘life-cycle analysis’. Recycled waste products could be used (from the building materials to substrate materials) or local products sourced rather than imported materials to reduce the energy used in these components. Some systems may require more water than others, but if that water is sourced from harvested stormwater or recycled water, it may be more sustainable than a low water-using system that uses potable water. Considered application of fertiliser is required to ensure there is no negative effect from polluted run-off from the site. Management of weeds and pests in the vegetation through a maintenance regime will also contribute to overall sustainability outcomes.