Green Roofs & Walls: Energy Efficient Building in Rio de Janeiro

Green roofs & green walls provide shading and reduce solar gain - they may be useful in Rio de Janeiro

Green roofs and walls help to reduce solar gain and can improve the energy efficiency of buildings. Photo by Chris Campbell licensed under creative commons.

Green or living roofs are a passive cooling measure which helps prevent solar radiation reaching a building. Green roofs are partially or completely covered with vegetation.

They incorporate a waterproof membrane and growing medium, into which appropriate plant species are planted. Root barriers, drainage and irrigation systems may also be part of the green roof.

Walls and facades can also be planted, creating so-called green walls. These can help to prevent solar gain by shading buildings. Green walls create an acoustic screen, helping to reduce noise pollution.

More research is needed to quantify the benefits of green walls, though it has been reported that living walls can reduce building cooling load by 28% [1].

The plants on green roofs (and green walls) provide shading and reduce solar gain. They also help to reduce the urban heat island effect caused by the re-radiation of heat from traditional building materials. Green roofs provide insulation, which can help improve efficiency in air-conditioned buildings [2]. Green roof systems also reduce flood risk by acting as a storm water buffer [3], and have the added benefit of helping people to experience nature as part of their daily lives.

Energy Savings

Green roof systems are becoming more widespread in Singapore, which has a similar climate to Rio de Janeiro [4]. Research in Singapore has demonstrated that green roofs on commercial buildings can reduce annual energy consumption by up to 14.5%. The planting of shrubs has been found to generate the greatest energy-savings [5].

Studies in Rio de Janeiro have demonstrated that the underside of green roof systems are significantly cooler (up to 12 deg C) than plain concrete roofs. It should be noted that the minimum underside temperature during night time does not fall as much in a green roof system, as the growth medium acts as an insulator [3]. These systems may hence be less suitable for buildings and building zones that have night-time occupancy.

The potential energy savings of green roofs should be balanced against the added embodied energy required for their construction. In addition, additional maintenance and irrigation requirements should be considered – especially with regard to green walls.

Green shading systems offer an alternative to green walls, and involve long-term growth over a pergola or wire-frame system. Such shading systems can help reduce urban heat island effects, and improve the well-being of building users.

Green roofs should be considered for buildings in Rio de Janeiro.

More Resources

The following links provide more information on green roofs and green walls:

References

  1. S. Loh, “Living Walls: A Way to Green the Built Environment,” Environment Design Guide, Built Environment Design Professions, 2008. [Online]. Available: http://www.environmentdesignguide.com.au/media/TEC26.pdf
  2. S. Tanner and K. Scholz-Barth, “Technology Focus: Green Roofs,” Federal Technology Alert, 2004. [Online]. Available: http://www.nrel.gov/applying_technologies/pdfs/femp_fta_green_roofs.pdf
  3. M. Laar and F. W. Grimme, “Thermal comfort and reduced flood risk through green roofs in the Tropics,” The 23rd Conference on Passive and Low Energy Architecture, Geneva, Switzerland, 2006. [Online]. Available: http://www.unige.ch/cuepe/html/plea2006/Vol2/PLEA2006_PAPER312.pdf
  4. Cairns Regional Council, “Sustainable Tropical Building Design: Guidelines for Commercial Buildings,” 2011. [Online]. Available: http://www.cairns.qld.gov.au/__data/assets/pdf_file/0003/45642/BuildingDesign.pdf
  5. N. . Wong, D. K. . Cheong, H. Yan, J. Soh, C. . Ong, and A. Sia, “The effects of rooftop garden on energy consumption of a commercial building in Singapore,” Energy and Buildings, May-2003. [Online]. Available: http://portal.jnu.edu.cn/publish/uploadFile/2970/eWebEditor/20100703062308895.pdf