Environmental benefits achieved by
living envelope interventions in cities



The paper explores the benefits achieved by such a green intervention analysing the contribution to ameliorate the environmental impact of cities focusing on the following: reduced cooling and heating demand; improved air quality; and reduced stormwater runoff. To achieve this, it studies previous research conducted in cities such as Tokyo, Japan; Madrid, Spain; South Africa; Toronto and Vancouver, Canada; Chicago and Seattle, USA. In addition it studies different technologies and construction systems for green façades, assessing the appropriateness of each system as they function within different urban situations.

The paper illustrates the first results of such a green intervention which would contribute to reducing buildings’ energy demands by 9%; CO2 emissions by 10%; and stormwater runoff by 4%. It concludes by explaining the environmental benefits which living envelopes offer to cities. Additionally, such results are only achieved when they are applied in the larger holistic scale of the whole city. Consequently, the analysis will need to provide a demanding evaluation tool to help governments and policy makers fully implement its hypothesis.



Industrial Context
This research provides an analysis of existing living wall systems, including a critique and proposal for the most appropriate system, depending on the project conditions. It categorizes living walls into two main types: opaque and transparent. The research analyses different construction systems suggesting which would be more appropriate in different situations.
This analysis is useful for the manufacturing, construction and installation of living walls, and ultimately for industry.

Various factors, including escalating urban population growth (United Nations, 2008); together with limited global natural resources (Hubbert) and the uncertain consequences of so-called climate change, position cities as key research subjects since they contain the collective pieces which contribute greatly to this dramatic situation. This research however, posits cities as not the problem, but the solution (Lerner, 2008).

Learning Objectives:
Two main learning objectives stem from this research:
• The environmental benefits achieved by greening a certain percentage of roofs, façades
and streets of an existing urban fabric. Research focuses on the following benefits:
• Energy demand reduction by buildings covered by living envelopes
• Air quality improvement by reducing and trapping air pollutants such as CO2
• Stormwater runoff reduction by living envelopes
• An analysis and critique of existing living wall systems.
The research provides an understanding of existing living wall systems and proposes a methodology for finding the
most appropriate system for different conditions.

The research proposes a holistic approach in order to respond to the aforementioned issues. Consequently, the research suggests increasing the greenery within cities through an overall living envelope intervention (including green roofs, green façades and green streets) as a means of ameliorating the existing environmental impacts of cities.



1. Introduction

In 2008, for the first time in history, the world urban population has equalled the world rural population (United Nations, 2008). According to future projections, the increasing urban population trend will continue. The consequences of this unprecedented urban expansion are dramatic. Cities are responsible for major health and hygiene deficiencies, consume three-quarters of the world’s energy, and emit at least three-
quarters of global pollutants (Rogers, 1998).

As an answer to this situation this research suggests that more greenery should be incorporated within the existing urban fabric. It proposes an overall living envelope intervention which includes living roofs, living walls and green streets. Such a green intervention would contribute to improved urban air and water qualities; reduce building energy demand and stormwater runoff; enrich urban biodiversity and expand urban agriculture capacity; reduce the urban heat island effect; contribute to improved civic aesthetics; and build upon broader carbon neutral city initiatives.

The research applies this hypothesis to a case study area in Downtown Vancouver. It proposes increasing existing green surfaces within the selected area by applying the Seattle Green Factor. This requires an expansion of existing green surfaces, by greening 30% of flat roof areas, 30% of sidewalk areas, and 15% of façade areas in order to achieve the value [0.3] suggested by the Green Factor. The research studies the influence of such an overall green intervention upon the urban environment. It focuses the analysis of such an intervention on three main aspects: air quality improvement in terms of reduced CO2 emissions; energy demand reduction by buildings and stormwater runoff reduction throughout the site.Living Envelopes - Arial PictureLiving Envelopes - Arial Picture


2. Methodology

In the first phase the case study site is selected within downtown Vancouver. The selected area, located in a dense urban area, combines residential and commercial buildings (Fig1). The residential neighbourhood is the West End, a neighbourhood from the 1960s, throughout which new high-rise buildings are still developing.

Living Envelopes - PlanFig1: The selected site in downtown Vancouver combines the residential
neighbourhood – West End – and Downtown District neighbourhood.



The research analyses existing site conditions in terms of land use; green versus grey surfaces; current energy consumption by buildings based on their usage; and CO2 emissions depending on the energy source. It also calculates current flat roof and building façade areas (Fig2 and Table1).

Living Envelopes - Plan

Fig2: Land Use and Grey vs. Green surface analysis of the selected site

Living Envelopes - Green vs. Gray

Table 1: Characteristics of the selected site


The research proposes to increase existing green surfaces. To this end the research analyses a series of green factor initiatives around the world. These green factors started in Berlin and Hamburg, Germany during the 1990s with the Biotope Area Factor (BAF 1994). Similarly, the Greenspace Factor was recently implemented (2001) in an urban development in Malmö, Sweden (Greenspace Factor 2001). Even more recently, in 2007, the City of Seattle, USA, developed its Green Factor (Green Factor 2007). Green factors promote increased green surfaces in cities and their main objectives could be summarized as follows:

- Safeguarding and improving microclimatic and atmospheric hygiene
- Safeguarding and developing soil function and water balance
- Creating and enhancing the quality of plant and animal habitats
- Improving the urban environment, reducing energy demand and CO2 emissions

Living Envelopes - Seattle green factor

The research applies the Seattle Green Factor which requires reaching a minimum value of 0,3, which means that about 30% of an urban area should be green. In order to achieve the 0,3 value suggested by the Factor, this research proposes to green 30% of existing flat roofed areas, 30% of existing sidewalk areas and 15% of existing building façade areas. By doing so, existing green surface areas increase from 12% to 28% (Figure 3).


Living Envelopes - Figure 3

Fig3. Grey vs. Green surfaces, before and after the proposed green intervention.

3. Contribution of the proposed green intervention

The paper explores, based on related research, the environmental benefits achieved by such a living envelope intervention. In this sense, the paper focuses on the contribution to reduce the energy demand by buildings, CO2 emissions, and stormwater runoff.

Living Envelopes - Before-after

3.1 Reduction of the energy demand

The influence of living envelopes on reducing buildings’ energy demand is achieved based on related research studies. These suggest that green roofs, green walls, and urban forests significantly reduce the energy required for space conditioning, and contribute to a reduction of more than 75% (Liu and Baskaran 2003). Similarly, living façades contribute significantly to the reduction of indoor air temperature in the summer, by reducing the external air temperature of a west-facing orientation by up to 4ºC on a clear August day in Japan; (Hoyano 1988) and by 5ºC in South Africa (Holm 1989). This cooling effect of plants could reduce the annual cooling energy use by 31%, and windbreak plantings around unprotected homes would reduce annual heating energy use by 15% (McPherson, Nowak et. al. 1993). According to computer simulations, in a warm climate such as Madrid, energy use reductions for cooling could reach up to 45% and heating reductions up to 23% (Laurenz 2005).

Considering these results, the research suggests that the proposed green envelope
intervention would contribute to reducing energy demand by 9%.

3.2 Reduction of C02 emissions

The analysis of the capacity of greenery to trap air pollutants is based on the research carried out by Valentin Schaefer (Schaefer 2004). This suggests that grassy plants (on streets) would trap 4.38kg/m• per year; shrubby plants (on green roofs) would trap 8.76 kg/m•; and climber plants (on green walls) would trap 6.57 kg/m•.

Based on this study, and considering the influence on the energy reduction explained in the previous section, this research suggests that the new greenery introduced into downtown Vancouver by the proposed living envelope intervention would contribute to reducing current C02 emissions by 10%.

3.3 Reduction of stormwater runoff

The proposed living envelope intervention would retain rainwater and consequently reduce runoff. In order to quantify to what extent this retention would amount, the research applies the Curve Number Method to the case study area. In this sense each cover type (roof, street, and green open space); together with the daily rainfall data for Vancouver (Environment Canada, 2006), has been calculated to achieve the runoff rate for each cover type. The calculation uses an average CN of 69 for the soil texture (silt loam or loam) with a moderate rate of water transmission (0.15 - 0.30 in/hr) (Cronshey 1986). As recent research shows that compacted urban soil can influence infiltration, the CN of 69 also assumes that the soil is hand-compacted (Pitt, 2002). In order to achieve a contribution by green roofs towards runoff reduction, this paper uses the updated Crop Coefficient Method (California Department of Water Resources, 2000), where the runoff reduction rate of a green roof is equivalent to the evapotranspiration rate. By combining this rate and the green roof area, the total runoff reduction of green roofs is achieved.

Consequently, the results of such a living envelope intervention show that by greening,
stormwater runoff would be reduced by 4%.


4 Living Façades Study

The research also attempts to provide an analysis of different construction systems for living façades, in order to facilitate implementation towards building the proposed green intervention. To this end, it classifies the different types of current living façades. It studies very diverse examples around the world and identifies them in different types of systems of construction. This study also provides a critique of the current practice of living façades by illustrating missed opportunities.

Currently, living façade construction can take the form of one of two major categories:
those attached to an opaque wall – opaque living façades; and those created on a transparent wall – transparent living façades. These in turn split into five smaller subcategories: greenery climbing through an opaque wall; greenery attached to an opaque wall as a green tapestry; greenery composed of green vertical panels; greenery between two transparent layers; and, greenery in the external layer and a transparent wall as the internal layer (Table 2)

Living Envelopes Table 2: Types of living façades

The research identifies the opportunities in living walls by condensing them into the following six attributes: the improvement in Human Comfort; the exploration of their Expressive Capacity; the influence in Air & Water Quality; the enrichment of the Indoor- Outdoor Relationship; and the contribution to Urban Biodiversity and Carbon Neutral Architecture. The research then develops a framework which enables the evaluation of the appropriateness of the different types of living façades.

In evaluating the six attributes, the framework reflects the crucial difference between the two main categories of living façades – opaque and transparent. Transparent living façades are visible from both the outside and the inside, creating opportunities between the living façade and the indoor space. This results in a higher performance than the opaque living façades, in terms of indoor comfort temperature, energy demand reduction, indoor visual comfort, psychological benefits, etc. On the contrary, opaque living façades can only partially achieve many of these opportunities, but they provide greater thermal insulation capacity. In addition, some of the attributes are only evaluated for opaque living façades, such as the acoustic influence, and others are only evaluated for transparent living façades, such as the influence on indoor visual comfort.

Therefore the framework enables the critique and evaluation of the different types of living façades in terms of the extent to which they accomplish the identified attributes. This in turn helps to determine their appropriateness under different conditions, and contributes to improving current design and construction practices in building living façades.


5. The proposal of Living Façades

The research, together with a local company called MUBI (Urban Biodiversity Interfaces), propose a living façade design following analysis on the different systems. In this sense, it designs a combination of opaque living façade as well as a transparent living façade. In order to make it as thin, light, and simple as possible, the living façade design is composed of four main layers:

- Moisture and root barrier layer
- Mineral wool layer
- Felt layer
- Plants which will be inserted in previous layers

These layers form a “sandwich” in which an irrigation system is embedded. This sandwich is attached to metallic studs or spacers through fasteners. The metallic studs or spacers are attached to a blank-opaque wall (Fig 3).

Figure 3. The design of the opaque living façade prototype.

This living facade is based on a hydroponic system, where nutrients needed for plants are introduced within the water of the irrigation system. The research is currently working towards monitoring this proposed living façade, through a test room, in order to achieve more accurate data on its performance.


Results and Business Impacts

Key Findings

The research results demonstrate that by greening a certain area of a city, the energy demand by buildings would be reduced by 9%. This results in a reduction of CO2 emissions by 10% and stormwater runoff by 4%. The research also provides a relevant classification system of living façades belonging to two main categories: opaque and transparent. The framework proposed to critique and evaluate the appropriateness of different living façade systems reveals differences in the behaviour of these two categories. It suggests that in order to achieve better energy performance in existing living façade technologies, opaque green façades would perform better for northern orientations, while transparent green façades perform better with the others, especially western orientation.

Business Impacts

Although this research currently lacks an accurate cost and benefits study, such a study is currently being developed, and could prove significant capital impacts. The study should be addressed with a focus on the cost of a living envelope intervention, which includes implementing living roofs and façades as well as green streets, with the result that such an intervention would contribute to overall energy demand reductions by buildings. Moreover, by incorporating green streets, the conventional urban infrastructure, specifically sewage infrastructure, could be abolished which would considerably reduce this infrastructure cost. Finally, what should also be taken into account is the easily quantifiable natural capital that this kind of intervention would contribute to, in terms of its contribution to urban wildlife biodiversity, human psychology and health, and ultimately to the urban environment.


This research shows the potential of a living envelope intervention. It emphasizes the need for proposing holistic green interventions in order to achieve significant contributions towards improving existing urban environments. However, the research highlights the need for a more in-depth study of the specific benefits of vegetated envelopes, particularly on green walls, in order to achieve more accurate data. As a result, the research had to make some assumptions such as the contribution of living envelopes towards reducing the energy demand by buildings, which have been made based on related studies such as the capacity of urban forests in reducing the urban heat island effect, etcetera. Thus, the research requires further specific research on, for instance, the influence of living façades in reducing energy demand, trapping air pollutants and retaining stormwater by monitoring it through test rooms. It suggests that the best way to achieve more accurate data is by monitoring living façades in terms of thermal performance including orientation, climate conditions, living façade systems, etc. This is the subsequent direction for the research.

The research also suggests there are many other environmental aspects of living envelopes which have scarcely been analysed. This includes the contributions towards enriching urban wildlife biodiversity, the influence on food production through urban agriculture; the contributions to carbon neutral architecture; and a cost and benefits assessment, among others. These studies would be crucial in order to clearly demonstrate the suitability of such living envelope interventions.


Key Lessons Learned:

• Environmental benefits achieved by the proposed living envelope intervention, focused mainly on the influence on energy, CO2 and runoff.

• In order to achieve significant improvements in existing urban environments, there is the need for overall green interventions, from a holistic concept, which includes green roofs, green façades and green streets.

• To achieve more accurate data the research requires further and more specific research, suggesting the monitoring of living façades in test rooms.

• The research provides a classification system of existing living façades, both evaluating them and suggesting the more appropriate one for different conditions.



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