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Tall buildings with "green" exterior walls improve air quality and audio+visual quality for all city residents.



In Justin Davidson's TED talk, he rails against increasingly ubiquitous glass towers dominating urban cores, citing reasons why he thinks this architectural style is worse than most alternatives.  At 9:16, he specifically offers an alternative of "green façades" like Milan's Vertical Forest, created by architect Stefano Boeri, highlighting greenery as its most visual feature:

That building "is one of the most intensive living green façades ever realized."

The same architect is now working on a similar design for Nanjing, China:

Artist's view

Another large residential project, using a technique requiring less balcony space, can be found in the Rosales neighborhood in Bogotá, Colombia:Residential building with green walls like vertical stripes between window columns.

Other sites for similar projects are in the works, and separate projects are found in other places around that city.  The city has terrible air quality, due in part to vehicle emissions from a large number of poorly maintained vehicles. 

This technique can also apply to nonresidential structures that might otherwise just have exposed concrete, such as in Mexico's Via Verde project (described as the world's largest of its kind; details below):

Air quality could become much better in cities if living façades were as common as glass or concrete ones are today.

Is this proposal for a practice or a project?


What actions do you propose?

Increase the amount of greenery found on the exterior of tall buildings.  Possibly alter building codes to require enough greenery in reasonably close vicinity of new buildings over a certain size to generate the oxygen needed for the intended occupants of the property, with a way to buy credits from nearby sites in the event that on-site oxygenation is not feasible.

Building codes and regulations could be set to make it easier for builders and building owners to know what they have to do to gain regulatory approval, and building codes raising standards on energy efficiency could incentivize use of these design elements.  Municipal or institutional owners could also decide that they will not erect any building without features like a living façade, though it is more common to set a standard based on e.g. the LEED rating scale overall (e.g. "as a formally adopted institutional rule, we will not build anything below LEED Silver.").

Although individual consumers may not have permissions to install a protective and then green layer on the outside of a tall building (see e.g. Via Verde docs for examples), they can increase demand for such spaces to incentivize developers.  They can also build "garden towers" on ground levels or sturdy balconies, to obtain many of the benefits outlined below (e.g. privacy, cleaner air, noise reduction, stress relief, potential health improvements, access to fresh edible greens, and with this composting tower, organics waste reuse.)

Homeowners could also implement this proposal by planting (especially deciduous) vines with trellis supports (a bit of distance from the house itself, allowing airflow for cooling) to provide summer shade and cooling closer to a house than would be appropriate for a tree.  These can also provide fresh food, when selecting a species like scarlet runner beans, winter squashes, and Luffa squashes. An example of a vine trellis for summer home cooling at the Duke Smart Home is pictured here (image licensed from Duke): An exterior photo of the Home Depot Smart House at Duke University showing the vine trellis.

Who will take these actions?

Building owners (especially for new tall buildings going up) will be the customer asking for these; architects should be made more aware of the benefits, and planning boards/building code regulators should be more informed about the real costs and benefits of these living façades.

Local governments could also express their support for such projects through public statements and/or policies such as building code modifications (see "what") or favorable tax treatment (e.g. the costs associated with building the living façade are not considered in property tax assessment, recognizing positive public externalities).

In response to Maria Repetto's comment, national governments could implement the practice, just like any other big organization, or provide funding and other incentives for the practice on the grounds that it can help meet a country's Intended Nationally Determined Contribution from the Paris agreement.

In addition to the architectural and green-roof contractors cited for their work in projects mentioned in this proposal, a startup Green City Solutions has patented a basic panel with integrated sensing and control systems that can be installed on a street, claiming the benefits of 275 urban trees in a footprint as small as as one square meter (3.5 with two benches).

In addition to the primary benefits, some building owners may use Green City's product or a direct installation for advertising, such as what PNC bank did at its headquarters in Pittsburgh. This 2,380 sq. foot living façade was the largest green wall in North America at the time of its construction for the G-20 in 2009, though it occupied a relatively small portion of the building's south wall (10 of 30 stories). It featured 602x2’x2’x4" thick panels of locally grown regional plants, each of which held 24 plants and roughly offset the carbon footprint of one person. It helped cool the building, with tests showing the wall behind the panels was 25% cooler than ambient temperatures.  This display lasted until late 2016 when other energy efficiency improvements were made and the bank erected a new skyscraper nearby (billed as the “greenest skyscraper in the world”), which partially shades the area. The bank moved the soil and plants to its Firstside Center park nearby. 

PNC Bank Pittsburgh Green Wall

Where will these actions be taken?

Especially new buildings particularly in dense urban cores. 

The countries listed below are not meant to be restrictive.  In the comments, Ralf Lippold suggests "including Denmark or the Netherlands as test regions, especially as these countries already put sustainability agendas in place."  Any area with sufficient conditions for growing the plants (i.e. maybe not the desert) and a need or expressed desire for the benefits could be suitable and also listed.  Given the restriction of only being able to list 5 countries, the ones that happen to be listed are those that seem to already have or be planning some sizeable projects, with some additional focus on the countries where the practice becoming widespread could have greater impact.



Country 2


Country 3

United States

Country 4


Country 5




A tall buildings database claims that each tower of Milan's Vertical Forest "is home to 480 big and medium size trees, 250 small size trees, 11,000 groundcover plants and 5,000 shrubs, which is equivalent to an entire hectare of forest cover."  The architect's page claims the complex has "900 trees (each measuring 3, 6 or 9 meters) and over 20,000 plants from a wide range of shrubs and floral plants distributed according to the sun exposure of the façade. On flat land, each Vertical Forest equals, in amount of trees, an area of 20,000 square meters of forest."

Here are statistics for one planned installation in China:

"The Vertical Forests together will feature 1,100 trees from nearly two-dozen local species, as well as 2,500 cascading plants and shrubs. The green area will span a combined 6,000 square meters, or about 64,600 square feet. The manmade forests will absorb 25 tons of carbon dioxide annually and produce about 60 kilograms of oxygen every day, according to the architects. 

Boeri's firm said it expected the green tower project would be completed in 2018. The team is also eyeing future projects in other major Chinese cities, including Shijiazhuang, Liuzhou, Guizhou, Shanghai and Chongqing."

For specific numbers, the Via Verde project is estimated to create oxygen for 25,000 people, filter 27,000 tons of gases, capture over 5,000 kg of dust and process 10,000 kg of heavy metals.

What are other key benefits?

Living façades can:

  • Absorb carbon dioxide from the atmosphere
  • Oxygenate air for local residents
  • Clean/filter out dust and fine particulate matter air pollutants
  • Help even out sudden temperature changes
  • Reduce noise pollution
  • Provide privacy for residents from others peering in
  • Beautify the urban environment, including seasonally changing views in temperate zones (e.g. the Milan "Vertical Forest" was elected the most beautiful skyscraper in 2015, and Best Tall Building by the Council on Tall Buildings and Urban Habitat).
  • Reduce stress
  • Reduce healthcare costs and secondary societal costs (e.g. lost productivity) for those in and around the living façade

The director of Mexico's "Via Verde" project cites the primary benefits are to reduce pollution/improve air quality while providing much-needed greenery to improve the cityscape and mood of the gray city's 20M residents. This will also reduce stress and improve productivity.  The World Health Organization recommends that cities have at least 9 square meters of green space per inhabitant, and Mexico City has only 3.7. This project, aiming for 40,000 to 60,000 square meters of greenery on over 1000 beltway columns, is only a small fraction of the 40M sq. m needed to catch up to that recommendation, but is a step in that direction. 

A Mexican Reader's Digest additionally cites direct and indirect job creation as a key benefit, especially for incarcerated women at the Santa Martha Acatitla Women's Social Readaptation Center who can do this work but would not otherwise have income. 

The project should also reduce healthcare costs for at least some of the 6 in 10 residents who have respiratory problems due to air quality. 

The initiative's source in a petition with over 80,000 signatures may also provide political benefits to the leaders who accepted it, though critics say that number is only a small percentage of the city's 20M residents.  Other cities in Mexico (e.g. Monterrey, Guadalajara, Querétaro and Puebla) and abroad (e.g. Los Angeles, Chicago, Dusseldorf and New Delhi have shown interest in replicating it).

Key benefits of Milan's vertical forest are cited that the vegetation "contributes to the reduction of energy consumption, creates a moist microclimate, acts as a filter for fine particles, greatly reduces noise pollution, cleans the air, protects from solar radiation and from wind."  The architect also cites the benefit of biodiversity and control over urban sprawl these tall structures promote.

Purdue University's 2nd place finish in the 2011 Solar Decathlon featured an indoor vertical living "Biowall" to naturally purify air, remove contaminants, and reduce the load on the mechanical ventilation system (which it was integrated with), in addition to being aesthetically pleasing.


What are the proposal’s projected costs?

In Mexico's Via Verde project, the gardens are metal frames with cloth (made with recycled PET bottles) put on top of the concrete pillars, to avoid damaging concrete.  Pockets are cut in the cloth to hold the plants and there's a rainwater-cistern-fed vertical watering system for each column (plus direct rain). The project cost is estimated at 300M initial + 2.3M MXN/month, which was about $14.7M +$113K USD/mo as of the date of the article/video containing that estimate (the same source also gives an initial investment number 1 order of magnitude lower, one must be a typo). The money comes from private investment, in exchange for using 10% of the columns as advertising.

Spanish and Portugese engineers have developed a multilayered organic concrete that more easily support plant life for living green façades, but the costs are not clear (at least to this author) as of this proposal authoring.


The modern technologies to do this are relatively new, according to the "Green Wall editor" at who noted in 2012 "the fact that beyond the work of the ever popular Patrick Blanc, the technology was still being developed for vertical walls." In 2015, he noted that "the living wall industry is still in its modern infancy" while still tracing their "history from the Hanging Gardens of Babylon through the first organized farms in Turkey to the Romans growing grapes on trellises."  Advances in materials technology (like the concrete noted above) can help make these more durable.  Advances in understanding about what plants and materials last and thrive in these settings are still being accumulated, though we have now built up several years of recent experience.  Because plants provide the benefits cited (cleaner air, noise reduction, carbon reductions, aesthetic benefits, etc.) on installation, timeline of impact depends primarily on how quickly the adoption of this practice increases.

About the author(s)

This proposal is open to wiki-style contributions.

Its initiator was a founding member and former leader of a residential college group focused on steps toward more sustainable living.  He is a Udall Scholar. He also resided in Pittsburgh, PA during the vertical display life of PNC's living façade, and traveled to cities in South and Central America viewing similar green walls there, as well as experiencing the terrible air quality and noise issues that motivate such walls in densely populated cities.  For most of the editing of this proposal, he had a direct view of a living façade that provided many of the listed benefits, but as it was not designed to be a living façade was probably damaging the wall materials the plants were clinging to.  

Related Proposals

There's already a lot of literature (and some proposals like Active Green Roofs, a 2013 finalist here) on "green roofs" which is relevant but not covered at length in this particular proposal.

Proposals focused on cities, like Low Carbon City Initiative: From Citizens To the World, also seem quite relevant.


Most references are hyperlinked in the text above, but here are a few additional references on the topic: