7.14 Building Design: Green Walls and Roofs

Author: Olivia Bailey

Date Submitted: March 4th, 2022

ABSTRACT

Applying greenery to the built environment can be beneficial for social, economic, and ecological factors. Green walls and roofs are applied to existing or new structures using a variety of methods that differ based on the building’s conditions, exterior climate, and client budget. Research has found that green walls and roofs can improve a building’s performance, promote energy savings, and increase structure lifespan (Manso et al.). However, they also have the potential to damage the building’s structural integrity and come with high installation and maintenance costs.

Chart showing average water retention for a traditional roof vs. a green roof. Source: “Green Roofs in the New York Metropolitan Region, Research Report,” Rosenzweig, et. al (2006).

MAIN

Green walls and roofs are vegetation that is planted over a waterproof layer system on a roof or a wall. They are also known as vegetative or eco-roofs, or vertical greenery systems. They require many specific layers that are not regularly found on roofs or walls. The anatomy used in these layers is not typical to garden or house plants as they require more drainage, structure, and aeration. Green walls and roofs are usually used to improve energy efficiency and contribute to biodiversity in interiors and architecture (Manso et al.).

There are three types of green roofs: intensive, semi-intensive, and extensive. Intensive systems use a deep soil substrate layer and require regular irrigation, which is ideal for the growth of most plants (Peck and Callaghan). They allow for a wide variety of plants such as shrubs, bushes, and small trees. Due to their thickness, they have good insulation properties, but put greater weight on the roof. Semi-intensive systems use less of a substrate layer than intensive systems and they require less maintenance (Peck and Callaghan). A variety of plants can also be offered. Extensive systems use a thin substrate soil layer and require little to no irrigation (Peck and Callaghan). This is not ideal for some plants but works well with succulents, moss, grass, and wildflowers. They require low maintenance and offer spontaneous growth.

There are two types of green walls, which are green facades and living walls. Green facades make use of climbing plants that grow against the wall or a support system such as a trellis. These walls grow slowly and have a limited plant selection. Living walls have uniform vegetation along the surface and use more of a variety of plant species. They can be modular, with individual trays, or continuous systems. Due to the variety of plants and uniform growth, living walls require more frequent irrigation and nutrient supply (Manso et al.).

Green walls and roofs are made up of nine components. Each layer has a specific function to protect the existing structure and keep the plants from dying. Some systems are installed in one large section, while others use separated, modular beds. The basic components are vegetation, growing medium, filter membrane, drainage layer, waterproof/root repellant layer, membrane support for plantings above, thermal insulation, vapor control layer, and structural support (Manso et al.).

Installing green walls and roofs have many environmental advantages, such as water retention benefits, thermal absorption, and improved air quality (Manso et al.). Specifically, green roofs retain greywater in their plants and growing medium, reducing stormwater entering the ecosystem and sewers. The substrate acts as a biofilter, treating the greywater (Manso et al.). Green walls and roofs can absorb heat through moisture retention, lowering the surface temperature. The extra layers can also serve as insulation & acoustic barriers. The plants reduce carbon dioxide produced by HVAC and mechanical systems, while also increasing oxygen production (Peck and Callaghan). These advantages result in energy cost savings, spending less on heating and cooling, or air filtration. The lifespan of green walls and roofs is also 40+ years, whereas regular walls/roofs last approximately 20.

There are some disadvantages to green roofs and walls, due to the extensive layers and maintenance, as well as the impact on the structure of a building. Green walls and roofs are more expensive than regular to install, and they require regular irrigation, nutrients, and other maintenance. The substrate can also be quite heavy, adding to the load placed on the building. The water and moisture due to irrigation can potentially be damaging to the building structure, and in some cases, can cause leaks.

Overall green walls and roofs can reduce carbon emissions and promote biodiversity. They improve a building’s energy efficiency but must be selected carefully when considering a building’s system and physical characteristics. 

RESOURCES

Manso, Maria, et al. “Green Roof and Green Wall Benefits and Costs: A Review of the Quantitative Evidence.” Renewable and Sustainable Energy Reviews, vol. 135, 2021, https://doi.org/10.1016/j.rser.2020.110111. https://www.sciencedirect.com/science/article/abs/pii/S1364032120304020

Peck, Steven W., and Chris Callaghan. Greenbacks from Green Roofs: Forging a New Industry in Canada. CMHC, 1999. https://commons.bcit.ca/greenroof/files/2012/01/Greenbacks.pdf

BIOGRAPHY

Olivia Bailey is currently in her third year at the School of Interior Design at Toronto Metropolitan University (formerly Ryerson). She believes that design should not just be about aesthetics, but should also be socially responsible: considering environment, culture, philosophy, and lifestyle. 

Leave a Reply