The following is a curated collection of direct quotations from multiple research studies published around the world in recent years related to the topic

Research available on green roofs is insufficient as there haven’t been long enough studies yet. Not only can green roofs be built to last 50 years while conventional roofs only last 20 years, it’s clear there are many direct and indirect long-term benefits of green roofs and walls, and the like. An overview of carbon sequestration of green roofs in urban areas - ScienceDirect

All climates

The results from climate modeling suggest that the occurrence of heat waves in the future will increase with higher peak temperatures because annual building energy consumption will increase by 9%, 17%, and 30% in 2020, 2050, and 2080, respectively. Green roofs to reduce building energy use? A review on key structural factors of green roofs and their effects on urban climate - ScienceDirect

Vertical greening systems provide personal and social benefits. The CBA determined that installation and maintenance services costs play a fundamental role on the economic sustainability. For some of the systems analysed in this study the benefits can not pay back these costs. The most relevant benefits calculated in this CBA are connected with the real estate and the energy savings for summer air conditioning. While all the benefits could be considered for studies based in other locations

Simulations have shown that in hot summer days, VGS leads to reduce exterior surface temperature of building facades, maximum of 26 °C. The annual cooling energy consumption is reduced by 3% for warm temperature climates. However, during the winter season insulation effect of VGS cause increase in heating demand of the building. Simulations suggest that, passive energy benefits of VGS are promising during summer periods, whereas it may disadvantageous during winter periods.Studying the potential of energy saving through vertical greenery systems: Using EnergyPlus simulation program - ScienceDirect

Covering the roof of an uninsulated building with plants reduces the amount of energy used in heating by up to five per cent in the winter, and the cooling energy by as much as 33 per cent in summer, which saves money. It also reduces daytime indoor temperature fluctuations in the absence of air conditioning.Green buildings can boost productivity, well-being and health of workers (theconversation.com)

Since the research was focused on counting fine dust particles on leaves and between different circumstances, the main conclusions that can be drawn from the presented results on particulate matter and vegetation are as follows:
Leaves form a sink for significant quantities of health-damaging particles from the atmosphere, with the potential to improve local air quality.There is a great difference on particle adsorption between leaves taken near a road and from the woods (urban area versus rural

However, the presence of vegetation in various forms alters the pattern of pollution dispersion differently. More specifically, the results indicate that planting trees (e.g., birch trees) close to the edge of buildings can decrease the air temperature by up to 2–3 °C at the pedestrian level. Increasing the cooling intensity of the vegetation from 250 to 500 W·m−3 results in significantly lower air temperature, whereas lower wind speeds result in a higher concentration of pollutants at the pedestrian level. A combination of green walls and trees is found to be the most effective strategy to improve the thermal environment and air quality.Buildings | Free Full-Text | A Parametric Study on the Effects of Green Roofs, Green Walls and Trees on Air Quality, Temperature and Velocity (mdpi.com)

CFD simulations of flow, energy and pollution were performed for three test cases and the results demonstrate how including a building in an urban design can aggravate the urban heat island effect (UHI), degrade air quality and cause pedestrian discomfort. As a result, mitigation strategies (e.g., green roofs, green walls and trees) to minimise these effects must be offered. Five scenarios were tested which differ in terms of bottom heating, vegetation’s cooling intensity and the magnitude of the wind speed at the inlet. The results showed that all vegetations reduced the average temperature, pollution dispersion and velocity magnitude at the pedestrian level. In addition to evaluating vegetations individually, the effects of combining these measures were also studied. The following main conclusions can be drawn from this study.

In comparison to green façades, trees are the most effective type of vegetation for lowering velocity due to the corner and downwash effects. Because it has a broader crown and can be planted anywhere on the street, it is the ideal option for pedestrian comfort. Green walls and roofs, on the other hand, are solely on the exteriors of building

Green roofs can be implemented in various styles and formats. Each technique may incorporate various design elements, such as diverse plant species and substrate compositions. Herath et al. [7] undertook an investigation using the simulation software ENVI-met to study the impact of installation of greening systems on the energy use of buildings. The green roofs, green walls, and combining all the strategies reduced the temperature by 1.87 °C, 1.79 °C, and 1.90 °C, respectively. The urban greening strategies of green envelopes are essential for reducing GHG emissions and lowering building-related energy consumption. Green envelopes minimized the heat transfer through building roofs by up to 80% [8]. Greenery systems with vegetation provide aesthetically appealing and thermally comfortable indoor and outdoor environments.

The energy needed to heat or cool a building is directly related to its thermal inertia [9]. Increas

Sustainability | Free Full-Text | Simulation of the Energy Performance of a Building with Green Roofs and Green Walls in a Tropical Climate (mdpi.com) he solar heat gained through direct sun-exposed walls of the conventional building was observed to be about 70% more than the building with a green roof and a green wall of 200 mm thick-vegetation layer.

Increasing Energy Efficiency: Residential Green Walls | asla.orgGreen walls provide similar benefits to green roofs, but also include:

Cost-efficiency: Through shading, green walls can lower temperatures in summer and reduce energy costs by 23 percent.
Reduced air temperatures: Temperatures behind green walls can be reduced by as much as 10 degree Celsius. Green walls also reduce temperature fluctuation at the wall’s surface, which can damage a building’s façade overtime.

Green Roofs: Advantages in Energy Efficiency - ANSI Blog

In fact, it has been found that an extensive green roof can reduce daily energy demand for air conditioning by 75 percent.

Read more at the ANSI Blog: Green Roofs: Advantages in Energy Efficiency https://blog.ansi.org/?p=7074

The purpose of this paper was to point out pros of using plants as the external wall covering, and to check the level of savings in heat energy consumption on the example of uninsulated building. The reduction of the heat transfer losses for analyze premise is not significant. The simple pay back time (SPBT) reaches quite high value that is lowered by the land tax exemption (guaranteed by the local city regulations). However it is important to underline, that there was no shading effect taken into account nor additional cooling effect during the summer was calculated. Apart this 00,10,20,30,40,50,61 2 3 4 5 6 7 8 9 10 11 12Energy demand, GJ/yearNumber of the monthheating7E3S Web of Conferences 116, 00096 (2019) ASEE19https://doi.org/10.1051/e3sconf/201911600096

North America

Lower air temperatures: A modeling study found that adding green roofs to 50 percent of the available surfaces in downtown Toronto would cool the entire city by 0.2 to 1.4°F (0.1 to 0.8°C).Increasing Energy Efficiency: Residential Green Roofs | asla.org

Several studies have demonstrated the important role of green against air pollution which affects urban air; in an urban street with trees there is only 10–15% of the total dust particles of a similar streets without trees [24]. Yang et al. (2008) measured the following rate of air pollutants absorbed by green roofs in Chicago: 52% of O3, 27% of NO2, 14% of PM10 and 7% of SO2.Cost–benefit analysis for green façades and living wall systems - ScienceDirect

The urban heat island (UHI) phenomenon can cause air temperature in the cities to be 2–5°C higher than those in the surrounding rural areas, mainly due to the amount of artificial surfaces (high albedo) compared with natural land cover and by atrophic activities [5]. Vegetation plays a fundamental role on the mitigation of the urban heat island [21]. A research conducted by Akabari et al. [22] shows that the mitigation of the urban heat island effect with trees, green roofs and green façades can reduce the U.S. national energy consumption for air conditioning up to 20%, saving of more than $10B in energy use.

'For residential green roofs, one of the core benefits is insulation, both from heat and also from the cold, so your energy bill goes down,' says Riane Hunt of Recover Green Roofs, LLC(opens in new tab), a green roof design and installation company in Somerville, Mass. 'Houses lose a lot of energy through the roof, and they intake a lot of energy on the roof, too. Green roofs retain a lot of water, which reduces the ambient temperature in the air around them.

Other climates

outcome, using the greenery on buildings is constantly desired action by the city governors and should be considered and deeply investigated in terms of utilization of buildings located in dense urban tissue. The work can be presented on the conference thanks to the founds of the Faculty of Environmental Engineering, Wroclaw Univers(PDF) The use of green walls and the impact on air quality and life standard (researchgate.net)

The meteorological weather station data is available at Iran’s Meteorological Organization (IMO). Furthermore, different green passive design strategies (GPDS) such as green roof and green wall are used by Design Builder model. The energy demand and CO2 emissions of a building with different structural scenarios during the current (2000–2019) and future climatic conditions (the 2050s) in two Hot-Dry (Kerman) and Hot-Humid (BandarAbbas) climate samples in Iran is simulated. it will not change by 2050s. Also, the maximum heating and cooling energy demand were calculated for the base building. Based on the results, green wall has more efficiency in optimizing total energy consumption compared to green roof in both climate types. On the other hand, GPDS are more efficient to optimize heating energy demand in comparison with cooling energy demand. Furthermore, the green wall strategy has better performance in reducing CO2 emissions as well. Accordingly, CO2 emissions reduce in Kerman by 2.73% and 2.93% by the implementation of the green wall during the observation period and 2050s, respectively. Meanwhile, this strategy can reduce CO2 emissions by only 1% per year in BandarAbbas during all studied periods.Mitigation of climate change impact using green wall and green roof strategies: comparison between two different climate regions in Iran | SpringerLink

therefore, this study aims to examine and compare the annual energy savings conveyed by green roofs and green walls on residential buildings in Malaysia. The findings indicated that green walls provide greater annual energy savings than green roofs. The result shows that green walls are able to provide higher annual electricity savings for residential buildings at RM166 compared to green roofs, which provide savings of only RM139.Comparison on energy saving: Green roof and green wall | Request PDF (researchgate.net)

. The analysis shows that the initial cost of a green wall is 15% higher than a comparable conventional wall. However, operational and maintenance costs of green walls result in 64% and 25% savings due to potential energy cost-saving, and minimum external redecoration time interval, respectively. This results in an overall LCC saving of 45% over conventional walls with a reasonably expected lifetime of fifty years. As a departing point of previous studies, this study provides empirical evidence on the LCC of green walls in comparison to a conventional wall in a residential facility, from a tropical climate perspective.ENERGY AND LIFE CYCLE COST SAVING POTENTIAL OF BUILDINGS USING GREEN WALLS: A CASE STUDY FROM SRI LANKA | Request PDF (researchgate.net)

This research shows that, in July, surface temperatures (STs) on the vegetated façade were up to 13 °C lower than on the unvegetated (bare) façade. Under the climate and environmental conditions of the green wall located at ENEA Casaccia Research Center (Italy), a saving Horticulturae | Free Full-Text | Vertical Greenery as Natural Tool for Improving Energy Efficiency of Buildings (mdpi.com)

Green roofs may be considered a passive energy saving technology that also offer benefits like environmental friendliness and enhancement of aesthetic and architectural qualities of buildings. This paper examines the energy and economic viability of the green roof technology in the hot humid climate of Saudi Arabia by considering a modern four bedroom residential building in the city of Dhahran as a case study

For the three investigated green roof options, energy saving is found to be in the range of 24% to 35%. Buildings | Free Full-Text | Energy and Economic Evaluation of Green Roofs for Residential Buildings in Hot-Humid Climates (mdpi.com)

The findings suggested that without any mitigation measures, residential building energy consumption in Qatar could increase by up to 9%, 17%, and 30% in 2020, 2050, and 2080, respectively. The addition of 5-cm expanded polystyrene and the installation of energy-efficient windows proved to be far more efficient than the addition of green walls and roofs under the climate conditions (30% reduction in energy consumption vs. 3%). Additionally, the environmental impact of green wall and roof maintenance, specific to Qatar, should be considered. However, in the final judgment, other positive effects of a green infrastructure (such as the effect on air quality, heat island effect, and health of the inhabitants) should be considered.

\The findings suggested that without any mitigation measures, residential building energy consumption in Qatar could increase by up to 9%, 17%, and 30% in 2020, 2050, and 2080, respectively. The addition of 5-cm expanded polystyrene and the installation of energy-efficient windows proved to be far more efficient than the addition of green walls and roofs under the climate conditions (30% reduction in energy consumption vs. 3%). Additionally, the environmental impact of green wall and roof maintenance, specific to Qatar, should be considered. However, in the final judgment, other positive effects of a green infrastructure (such as the effect on air quality, heat island effect, and health of the inhabitants) should be considered.Efficiency of green roofs and green walls as climate change mitigation measures in extremely hot and dry climate: Case study of Qatar - ScienceDirect

The main goal of this study was to evaluate the feasibility of such measures under a subtropical desert climate, which is characteristic of Middle Eastern regions. As a case study, a residential building stock of Qatar was considered. Based on an architectural survey and observation, a detached two-story family villa was chosen as a representative of the stock and was used as a case study. Weather conditions were projected for the years 2020, 2050, and 2080, and three energy demand increase mitigation measures were considered: the addition of (1) a green roof, (2) green walls, and (3) thermal insulation of the building envelope with expanded polystyrene along with the installation of energy-efficient windows.

This article discusses in detail the effectiveness of using the green walls and roofs on the internal thermal comfort to reduce the building’s temperature in the desert regions like Ouargla in Algeria, using a model room and experiments in the summer. The investigation is based on a measurement campaign carried out every half hour. Several physical parameters have been treated, such as air and surface temperatures, and air humidity. The effect of vegetation on the hygro-thermal environment of buildings was studied by comparing the performance and quality between five rooms “a, b, c, d, and e. The results showed that the use of vegetation on the walls for rooms “a, c,” also the wall/roof of room “e,” decreases the temperature of the air by evapotranspiration of water. In addition, the vegetation reduces the surface temperature by the shade it provides, with a temperature difference between the three rooms. The lowest value of air temperature reduction is 2.8 ℃ in room “e”.Effects of green roofs and vertical greenery systems on building thermal comfort in dry climates: an experimental study | SpringerLink

Studies demonstrate that a vertical green layer can contribute to the building envelope performances by creating an extra stagnant air layer which has an insulating effect [13] and reduces the energy demand for air-conditioning up to 40–60% in Mediterranean climate [14], [15].

The Green Roof Energy Calculator is an online tool that allows users to compare the annual energy performance of a building with a vegetative green roof to the same building with either a dark roof or a white roof.

Simulations are available for new construction (ASHRAE 90.1-2004) and old construction (pre-ASHRAE 90.1-2004) office and residential buildings driven by typical precipitation and weather data. Representation of an irrigation schedule is optional.

Green Roof Energy Calculator | Urban Climate Research Center (asu.edu)

LAPT:

The LAPT was developed over five years with input from hundreds of academic and industry professionals. It was introduced to the market in 2018. The LAPT is a 110-point performance rating system that includes a comprehensive overview of all the performance benefits attainable from green roofs and walls across eight major categories, such as water, biodiversity and maintenance. It can be applied to a green roof, a green wall or a combination of both. Based on the same framework in USGBC’s LEED and ASLA’s Sustainable Sites, the LAPT provides a tool for designers wishing to get the most benefits for their projects.

The LAPT is a useful third-party review mechanism, to determine if a project is certified, silver, gold or platinum. Third party reviews are conducted by the Green Infrastructure Foundation, do not require excessive documentation, and are a fraction of the cost of other certification systems. To date, a handful of projects have been certified by this quality assurance framework, but the potential and need for more certification is huge. Click here to obtain a free copy of the LAPT.

The LAPT provides designers with insights into maximizing green roof and wall benefits and building owners with third party performance review and certification. Photo: Green Infrastructure Foundation

Green Roofs & Walls: Global Impact

All climates

North America

Other climates