Cost considerations

Each roof, wall or facade will vary significantly in terms of cost, depending on the design site, the system installed and the construction materials used. Costs can be reduced in small projects as ‘do it yourself’ (DIY) installations, involving less personnel and smaller spaces. There may also be economies of scale for large projects which will bring costs down, especially if there are other efficiencies in terms of access for construction, and if the build already lends itself to a green roof, wall or facade.

The long term savings should be considered when analysing costs, for instance a green roof might provide energy savings over the life of a building, because of its effect of cooling the structure.

Generalisations of costs, based on 2013 prices, are provided here, and are indicative only as each project will present different opportunities and challenges. The case studies included in this guide (see here) provide an indication of costs of particular installations (at the time of their construction). Up-to-date pricing, and advice on the costs likely to apply to a particular project site, need to be sourced from expert practitioners, providers, architects and engineers.

Construction costs will vary according to some of the following issues:

  • type of structure (and any need for structural reinforcement)
  • design
  • site location, size and access
  • distances for transport
  • storage of materials on or off-site
  • access for mobile cranes, access to goods lifts
  • roof height, dimensions and load-bearing capacity
  • roof construction, complexity of roof design including roof penetrations
  • timing of project, including contract growing of plants

Typical maintenance costs include irrigation water, fertiliser, replacement plants, weeding and pest and disease management. Periodic inspection and maintenance of the site, from the irrigation system to clearing drains to re-tensioning of cables or repair of loose wall fixings, will be needed. Maintenance costs may include access costs if, for instance, an elevated work platform is required (more information on maintenance can be found here).

A design contingency to cover additional costs during the development of the design of the green wall, facade or roof should be budgeted for, as should a construction contingency for unexpected problems arising during installation.

Green Roofs

It should be noted that it is significantly cheaper per square metre to install a green roof on a new building than to retrofit an existing building, as the structural load-bearing capacity can be more easily integrated into a new project compared to augmenting the structural capacity of an existing building.

Notwithstanding this, it is feasible to retrofit many buildings, either by providing additional structural supports or a new ‘floating’ roof to carry the green roof.

A small green roof (30-50 m2) with reasonable access would cost between $150 and $400 per square metre to install. This does not include:

  • design fees
  • planning and building permits
  • permits for lifts and cranes
  • demolition or relocation of existing infrastructure on the roof
  • addition of specific hard infrastructure elements, such as furniture, shade structures, decking, paving, planter boxes or structures to support climbing or trailing plants.

It also assumes that the roof has sufficient structural capacity and does not require strengthening.

Example costs for strengthening the roof:

Existing roofs may require additional strengthening work in order to accommodate the weight of people, plants, substrate, and other items. The following rates for strengthening an existing roof can be used as a guide. Please note that these costs may vary according to the issues outlined above under ‘Cost considerations’.

  • Strengthen concrete roof slab under trafficable areas   $450-$650/m2
  • Strengthen a steel roof    $240/m2
  • Additional column supports and foundations     $2,500 to $7500 each

Example costs of individual components of green roofs:

The following rates for green roof components can be used as a guide; however, these costs may also vary according to the issues outlined above under ‘Cost considerations’.

  • Waterproofing       $100/m2
  • Drainage and protection layers     $20-$30/m2
  • Growing substrate, plants, irrigation     $100-$500/m2
  • Edge restraints       $50/lin.m
  • Paving, decking, flooring    $200-$400/m2
  • Balustrading  $150-$300/lin.m
  • 100,000L tank, pump and associated equipment   $25,000

Green Walls

DIY individual wall components for retail sale may be relatively cheap, at $160/m2 for the system and $150/m2 for the substrate, plants and irrigation system.

A professionally installed wall will cost between $1,100 and $2,800/m2 and will often include maintenance visits for 12 months in the price.

Green Facades

Professionally installed green facades will cost from $400/m2 upwards. DIY facades can be established more cheaply.

Example costs of individual components of green facades:

The following rates for green facade components can be used as a guide. Please note that these costs may vary according to issues outlined above under ‘Cost considerations’.

  • Climbing structure, including installation    $150-$350/m2
  • Substrate, plants and irrigation in planter boxes   $100-$150/m2
  • 15,000L tank including installation    $10,000

Contingencies and other fees

In professional quotes the following contingencies are often allowed for, in addition to the construction/installation costs of the green roof, wall or facade:

  • Design contingency of 10 per cent

An amount included in a construction budget to cover additional costs for possible design changes.

  • Cost escalation of three (3) per cent

Anticipated changes in the cost or price of labour or materials over a period of time.

  • Construction contingency of five (5) per cent

An amount included in a construction budget to cover unforseen situations/costs arising during construction/installation.

  • Consultant fees of 10 per cent