Topic 4

Various authors have presented general constraints, barriers and limitations in the establishment of green roofs.

Li and Yeung (2014), through a literature review, list the following constraints:

  • increase of maintenance, construction and design costs,
  • lack of incentives and promotion from the government towards developers, building owners and among communities (this is related also to a lack of awareness),
  • technical difficulty in design and construction,
  • the old age of buildings and/or weak structural loading for applying green roof.

Peck and Callaghan (1999) list four main barriers to green roofing:

  • lack of knowledge and awareness on behalf of policy makers, professionals, researchers and the general public,
  • lack of incentive to implement by local governments,
  • cost-based barriers,
  • technical issues and risks associated with uncertainty.

Vijayaraghavan (2016) also presents various constraints to the implementation of green roofs such as cost, maintenance, their character as ‘green’, lack of localised research, roof leakage or problems with their ultimate disposal.

We explore more in depth Vijayaraghavan’s (2016) barriers to green roofs.

Green roofs have often been ‘accused’ of being long-term investments with short-term returns. This pertains to their cost.

  • Their installation requires significant investment while their cost varies according to type of roof.
  • The operation, maintenance and ultimate disposal of green roofs are additional costs.
  • At the same time, there have been contrasting study results in relation to green roof cost, primarily due to the variety of locations that roofs can be installed.
    • Clark et al. (2006) argued that green roof installation has 27% higher cost than conventional but that the net present value over 40 years is at about 25% lower.
    • Lee (2004) on the other hand, found that green roofs are 7% more expensive than conventional ones considering extended roof life, energy savings and stormwater fee reduction.

An additional barrier for the installation of green roofs is what is perceived as their demanding and time-consuming maintenance.

  • Maintenance is an aspect that confuses building owners as often green roof developers make unrealistic assurances regarding minimum irrigation, fertilisation and weed clearing.
  • In reality, green roofs need watering, especially during draught climates, and occasional fertilisation, which in turn promotes weed growth and thus often maintenance checks.
  • Generally, the extent and frequency of maintenance depends on the type of roof.
    • Extensive roofs generally require only basic plant protection, drainage checks and weed removal.
    • Intensive roofs require more detailed maintenance operations.

An important question raised by researchers relates to how green are green roofs (Bianchini & Hewage 2012).

  • Aside from the growing medium and vegetation, the rest of the green roofs’ components are made of polymeric materials, in order to counter weight limitations and roof-top conditions.
  • It has to be stated though that drainage and filter layers are manufactured with recycled polymeric materials, while the pollution released in the air can be balanced by green roofs in the long term.

Another issue in relation to green roofs is the fact that there is very limited research on local environments.

  • Developers and policy makers in countries that exhibit limited research potential are thus unfamiliar with components suitable for their geographic location.
  • Imported components for green roofs often lead to high installation costs or possible failures due to non-compatible features.

A well-known assumption in relation to green roof installation is that it enhances the chances of leaking.

  • That is technically incorrect; research has shown that green roofs generally improve the life of roofs (Oberndorfer et al. 2007, Claus 2012).
  • Kosareo and Ries (2007) stressed that extensive roofs have the capacity to improve the life span of roof system up to 25 years.

It has to be stated nonetheless, that properly designed green roofs are needed in order to avoid structural damage to buildings. Careful assessment by experts, selection of proper components and examination of properties are prerequisite.

A limitation of green roofs not often considered is the ultimate disposal and the concerns it generates in terms of man-power requirements, cost and environmental implications.

  • The presence of plastic materials, especially in filter and drainage layers, presents few problems.