Urban Evolution

September 2014

The Exostructure

Sep 30, 2014 6:00 PM
by Daniel Calero

Posted by: Daniel Calero Jimenez
Toronto, Ontario, Canada



 Commerce Exo skeleton - daniel.calerojimenez - Flickr
 The future of our old buildings looks promising


I believe the society we live in today evolved in an era where ignorance of man’s symbiotic relationship with the natural environment greatly contributed to the conventional paradigm of thinking. As such, many of mankind’s largest technological advancements have undervalued the importance of long-term thinking in relation to ourselves and our surroundings. With this in mind, I felt it was important to propose an alternative paradigm that would be effective now and decades into the future in transforming my city- the City of Toronto- into a symbiotic city. Within this post, I will demonstrate how my proposed idea, which I call the Exostructure, is effective at bringing Toronto a step closer to net-zero energy through a transformation in building design, while also providing the future potential to facilitate 7 of the 9 most important transformations for a symbiotic Toronto.   


A Building Design Transformation: “The Exostructure”

The Exostructure could be initially visualized as a passive greenhouse that surrounds existing and new, mid to high-rise buildings. ‚Äč‚ÄčThese Exostructures would be partially or fully enclosed structures composed of a solid framework that provides structural support as well as dynamic electro-chromatic glazed glass (Dynamic Glass) to control solar gain and daylighting. By acting as an additional exterior envelope, the Exostructure will perform two main functions: 

  1. It will enclose buildings in more optimal microclimates (warmer in the winter and cooler in the summer), thus greatly reducing the load on a building’s interior heating and cooling equipment.
  2. It will become a structural support system for above ground infastructure, increasing urban vertical density and allowing cities to free up ground space for ecosystem regeneration.
Commerce Exostructure Icons - daniel.calerojimenez - Flickr
A dynamic envelope that keeps old buildings cool in the summer and warm in the winter


The three pillars of the design that facilitate the main functions of the Exostructure are the structural framework, the use of Dynamic Glass, and the passive heating and cooling systems.The structural framework of Exostructures could be made out of conventional structural materials such as steel, concrete, and aluminum or even a combination of these based on its future applications. Moving the support structure to the exterior allows for unobstructed open floor plans and an excellent use of daylighting. Also, as previously mentioned, when designed to support additional loads this external support structure becomes an infrastructural support system that is available to its surroundings. This will prove to be essential as cities continue to densify and we continue to expand our cities skyward. In cities like Toronto, with serious traffic congestion issues, this could assist transitioning to net zero-carbon mobility by providing more room and accessibility for pedestrians, cyclists, and public transit (discussed further under ‘Impacts’). Furthermore, this framework could be made out of prefabricated modular components and could be assembled like lego pieces. This would allow the Exostructure to grow over time, supporting a building that is continuously evolving and expanding.

The remaining surface area on the envelope could be partially or fully enclosed by Dynamic Glass based on the region’s climate. Dynamic Glass reacts to the outdoor climate and electronically adjusts its tint to control solar gain while reducing glare and harvesting daylight to preserve the view. This glass requires no electromechanical components, is very energy efficient (60W per 1800 sq.ft of glass), and can reduce cooling load up to 67% in a traditional setup [1]. I believe that when applied to the Exostructure, overall impacts on cooling and heating will be much greater. In warmer climates, the windows will resist heat transfer through the glass into the space between the Exostructure and the core building. This space will then act as a thermal chimney for any heat that does build up, ventilating hot air up and out of the structure through natural . In cooler climates, the opposite will occur, the glass allows maximum solar radiation to penetrate and the structure will enclose a warm blanket of air around the core building.

If high thermal mass materials, such as concrete, are utilized as part of the structural framework of the Exostructure, passive radiant heating and cooling throughout the thermal mass could be used to efficiently control the temperatures within the Exostructure’s microclimate. Cold water supply or warmer grey water could be run through a heat exchanger, heating or cooling glycol that would loop through the thermal mass to provide larger energy savings. For example, during warm seasons, cold water supply could be diverted to cool glycol that would be run throughout the thermal mass structure, cooling the Exostructure while also pre-heating the water supply. During cooler seasons, warmer grey-water (on average 18-38°C [2]) could be diverted to heat the glycol which runs through the thermal mass structure, which will provide heat within the Exostructure for extended periods of time. Alternatively, for buildings that don't have grey water collection systems, a solar thermal water heating system could be installed to achieve the same passive heating results.  


Exo Hot Climate - daniel.calerojimenez - Flickr
Diagram of how Exostructures can passively maintain buildings in cool microclimates


Through this design, additional increases in heating and cooling effeciency can also be attained by utilizing heat pumps, as well as, capturing and storing waste heat from the surrounding environment within the Exostructure. In residential settings, air-source heat pumps, which are not usually utilized in cold climates, could now become efficient alternatives to old central heating and cooling systems. This is because the outdoor heat pump compressor can operate more efficiently in the Exostructure’s more favorable microclimates[8]. Additionally, utilizing heat pumps within buildings enclosed by an Exostructure can prove to be a very effective way of pumping hot or cold air that is escaping a building and trapped within the Exostructure back into the building. 

Exostructures can also help buildings store free thermal energy located within its environment. For example, in cold climates, buildings located on top of busy underground pathways/subway stations can vent rising excess hot air into the Exostructure where it will be stored to maintain the building’s warm microclimate. This would make use of heat that is usually lost to the atmosphere and greatly reduce the energy demand for heating buildings in the cold climates.



Transforming to a Net-Zero Carbon Energy Economy:

I believe that renewable energy will be a key factor for converting our cities to a net-zero carbon energy economy. However, I also believe that we must reduce our demand for energy (which, globally, is heavily reliant on fossil fuels[12]) in order to assist this transition to renewables within the near future. Considering that over two thirds of the energy that we consume in Canada is used up by our buildings [4], and that much of that energy is consumed for space and water heating (about 80% in the residential sector in 2009[5]), it is extremely important that we increase the energy efficiency of our buildings. This is especially true given the fact that cities are expected to grow astronomically with an estimated urban population growth of 84% by 2050 [6]. This means drastically increasing urban densities which will completely change the way we build our cities. However, what will we do with our existing building stock, which, when compared to new construction in Toronto, has accounted for about 98%[7] of the total building stock in the last few years? Most of these existing buildings will eventually become obsolete, if they have not already. Do we simply demolish and rebuild, and if so, will the new buildings’ energy savings offset the energy required to rebuild them within a reasonable time period?

Rebuilding our cities from the bottom up is simply not a feasible nor a sustainable option. Instead, we must find a way to adapt our existing cities to deal with our ever changing needs in a way that is symbiotic with our environment. As previously discussed, the Exostructure can have the potential to drastically increase the energy efficiency of our existing building stock and allow us to continue building on top of these buildings instead of expending large amounts of energy to completely redevelop the land. Therefore, Exostructures can have a large impact in decreasing overall energy demand and easing the transition to renewable energy production and a net-zero carbon economy. It is also worth to highlight that Exostructures can have very dynamic applications in new construction buildings as well (discussed futher in 'Future Adaptations'). However, as previously stated, their greatest impacts today will be seen in using these structures to increase the energy effeciency of our existing buildings.  

A Framework for Mixed-Use High Density Planning:

As previously mentioned, the Exostructure makes it possible to build over existing buildings. This can substantially increase mixed-use density in urban areas. Each building would become a conglomeration of various stacked projects being supported and enclosed by one Exostructure. Office buildings could now be stacked with above ground parks, vertical farms, retail, and residential strata. Each building would constantly be evolving with the current needs of its inhabitants. All the necessities for a perfect live, work, play balance can be enclosed within one structure that wouldn’t take up much more space than an initial building’s footprint. These buildings could also be connected through infrastructure that is attached to the Exostructures, like enclosed interconnected walkways and bridges, cycling highways, and above ground public transit. This type of infrastructure would promote walkability, livability and contribute to a very successful mixed-use high density urban area. Also, to promote the open nature of these conglomerate buildings, each Exostructure would be co-owned by its community (residents and building owners) which would decide how their building is to grow and evolve into vertical communities. Furthermore, government incentives could be provided to owners for permitting the attachment of other infrastructure to the Exostructure.


EvolutionEvo2 - daniel.calerojimenez - Flickr
Buildings can now elvolve with time into mixed-use high density vertical communities


Transitioning into Zero-Carbon Mobility:

In high density areas the Exostructures may actually encroach on pedestrian sidewalk space. However, the solution to this problem may actually also help aid Toronto’s severe congestion problems. With municipal co-operation, these high density streets could begin transitioning into pedestrian friendly zones- which, when done properly, have proven to be a great way of dealing with traffic congestion (as seen in Europe and now more often in South America). Initially, the municipality could extend sidewalks, which would reduce the amount of space for cars and provide enough room for Exostructures to be built over a portion of the original sidewalk. Then, similar to what is being done in Buenos Aires with great success[13], these zones could be deemed shared pedestrian streets. The speed limit would be greatly reduced and the entire space could be shared by pedestrians, cyclists and slow moving vehicles during specific hours of the day. The intent is to slowly reduce the amount of personal motorized vehicle transit in high density areas by promoting other forms of transportation like walking, cycling, and public transit. The end goal is that an optimal portion of Toronto’s high density core will transition into full-time pedestrian friendly zones, bicycle paths and exclusive public transportation routes like BRT systems instead of congested roads.


Exo pedestrian zone - daniel.calerojimenez - Flickr


While this may actually increase the load on public transit, these Exostructures will also be providing infrastructure for future expansions of above ground transportation infastructure and public transit projects like a monorail system. Pedestrian and non-motorized traffic will also be diverted through above-ground walkways (like the Toronto Skywalk and the Centre Pompidou in Paris) and bicycle infrastructure (like the “Cycle Snake” bike bridge in Copenhagen), all which would be supported by the Exostructure.


Collage Skywalk - daniel.calerojimenez - Flickr


Exo city transport - daniel.calerojimenez - Flickr
What a zero-carbon mobility city may look like with Exostructures supporting transportation infastructure


Regenerating Ecosystem Services Infrastructure:

The Exostructure can positively impact the regeneration of ecosystem infrastructure in a few ways. For example, as more space for infrastructure becomes available above ground, more room on the ground can become vacant to allow the natural ecosystem to regenerate. Furthermore, in the future Exostructures may be able to support buildings off the ground (I call them “Floating buildings”, although technically they are still supported off the ground by the Exostructure), freeing up entire building footprints for green space. I envision these green spaces as native vegetation parks with escalators or elevators that lead up into the building.


Floating building - daniel.calerojimenez - Flickr
Elevated buildings will free up space for recovering green space


A series of above ground parks or "vertical parks" could also be constructed within vertically stacked buildings. These parks would be similar to a green roof but more elaborate with a climate that is controlled by the Exostructure surrounding it.  These natural areas could also be used to perform specific services like rainwater and greywater collection and purification.

CollageVerticalParks - daniel.calerojimenez - Flickr


Also because the Exostructure can maintain a steady microclimate, a large amount of vegetation can be maintained year round within the enclosed structure. This would provide much needed ecosystem services like air purification within the building(s) enclosed by the Exostructure. Inhabitants could now open their windows to clean air produced by plants as opposed to the smog and vehicle pollution that is so common within our urban areas.


Implementation Within Toronto

Based on the discussed impacts that the Exostructure may have in cities like Toronto, I decided to look at the Old Toronto district as a perfect example of where these Exostructures could be first constructed. I picked this area because:

  1. It is a high density area.
  2. It is composed of some of the oldest mid-high rise buildings in Toronto.
  3. Specific streets in the area could benefit by transitioning into pedestrian friendly zones.
  4. It is in close proximity to Union Station, Toronto’s busiest transportation hub, and thus may benefit in the future from above ground expansions to the transit system.

Within the Old Toronto District I chose the Commerce Court North Tower to demonstrate what the first Exostructure may look like. This building was built in the 1930s and, at the time, was the tallest building in Toronto. Since then it has become obsolete and does not employ many of the green technologies that some of the newer more effecient buildings have today. The first Exostructures to be built should be constructed for the main purpose of testing the system's ability to increase energy effeciency of its core buildings. The image below shows the Commerce Court North Tower with, what could be, one of these preliminary Exostructures. Once these Exostructures are fine tuned for energy efficiency, we can start exploring how to construct them as support systems for infastructure. 

Before After - daniel.calerojimenez - Flickr
Future Adaptations

Regenerative Building Fabric:

  • As cities continue to grow taller, less sun may reach ground levels making it more difficult to regenerate ecosystem infrastructure. If incorporated into the Exostructure, Green walls could provide much needed ecosystem infrastructure at higher altitudes providing CO2 sequestration and storm water retention services. Green walls could also provide extra insulation and cooling in hot conditions through evapotranspiration.
  • The structural framework of the Exostructure could contain smog eating materials like photocatalytic concrete.  Photocatalytic concrete contains titanium dioxide which breaks down NOx emission under sunlight. These nitrates are then washed away off of the surface of the concrete and could be collected and utilized as a fertilizer in an urban food production application as described below [3].

Urban Food Production:

  • Vertical farms may very well be the future of large-scale urban food production. The Exostructure can provide the flexibility to add these farms on top of existing buildings. They can exist within fully enclosed building extensions, open structures, or even stackable modular units supported and enclosed by the exostructure. Solar radiation and climate would be controlled by the Exostructure to support ideal growing conditions. Also, due to the support structure being located on the exterior, it would be easier to design vertical farms with shapes and layouts that can adequately distribute sunlight.

Material Recycling:

  • The Exostructure could provide the necessary framework to streamline large-scale modular building construction. Buildings could be pre-built in factory warehouses and then stacked onto the Exostructure supports. This could have great impacts for building deconstruction and repurposing, as modular components could be repurposed and reused in other buildings with an Exostructure.


Reuse - daniel.calerojimenez - Flickr

Infrastructure that Supports Resiliency

Climate change will drastically alter the way we do almost everything. Temperatures and UV radiation will eventually become so high that in many regions it will no longer be safe to remain outdoors for prolonged periods of time (heat related deaths are expected to increase by 257% by 2050, and 535% by 2080 [9]). Flooding, hurricanes, earthquakes, and other extreme weather phenomena will affect urban populations more frequently and severely[10]. If our urban infrastructure is not adapted to withstand these changes in climate, human survival will progressively become more difficult.

The Exostructure has the potential to help us protect our cities from the harsh changes in our urban environments. First and foremost, the Exostructure's ability to control the interior climate and reduce solar infiltration can protect people from rising temperatures and UV radiation. Also, interconnected walkways and bridges between Exostructures could allow people to travel within the city in an enclosed, cooled, and protected environment. The ability to construct buildings elevated off the ground onto the Exostructure could also protect buildings from being affected by flooding. In the case of a power outage, the Exostructure’s dynamic glass could remain in a tinted state for hours before becoming clear again[11] while the passive heating and cooling systems would continue working to maintain comfortable microclimates around its core buildings. Lastly, a network of interconnected Exostructures could provide the necessary reinforcement to withstand earthquakes, hurricanes, and other extreme weather events.

Closing Remarks

The cities that we live in today were not built by us, they were built for us. With that in mind, I think we need to start asking ourselves whether the cities we are building today will be supportive of our future generations. When conceptualizing ideas for my city, the most important question that I asked myself was whether or not this design would be instrumental to a city that I could envision my children thriving in. I believe that the Exostructure has the potential to go beyond that and add a completely new dimension to how all our cities function and perform in a constantly evolving urban environment.   



The inspiration for the Exostructure stemmed from my summer research on GEMINI Nested Thermal Envelope Design (GEMINI NTED)™ with Professor Pressnail at the University of Toronto’s Building Science department. NTED was developed to improve energy efficiency in historic buildings while maintaining the original facade. NTED requires the implementation of an additional thermal envelope within the interior of a building to surround and insulate core-designated areas. The concept was implemented into the Gemini house at U of T, reducing the historic home’s energy consumption by about 80%. The success of this project led me to search for ways which we could re-apply the GEMINI NTED concept for larger inefficient buildings. The result of this was the Exostructure, a dynamic structure that was meant to improve building performance and mutually support the evolution of our cities. Professor Pressnail kindly provided me with some well needed statistics and also helped me develop my ideas on using thermal mass within the Exostructure to control microclimate temperatures. Also, Ekaterina Tzekova and Adam DiPlacido, graduate students within the department, provided me with some direction in the idea generation process as well as helped point out some of the weaker points of my ideas. I would like to kindly thank everyone who has helped me with this project, it has truly been a fun ride! I hope you enjoyed reading it as much as I enjoyed piecing it all together.



[1] Carpenter, John. "Emerging Approaches and Technologies for Net-Positive Design." Building Lasting Change CaGBC National Conference and Expo 2014. Metro Toronto Convention Centre, Toronto. 3 June 2014. Lecture.

[2] Elmitwalli, T. A., M. Shalabi, and R. Otterpohl. "Grey Water Treatment in UASB Reactor at Ambient Temperature." Water Science & Technology 55.7 (n.d.): 173-80. Stanford University, 2007. Web.

[3] "Building a Better (Cleaner) World in the 21st Century." Self Cleaning Concrete. Portand Cement Association, n.d. Web.

[4] Behidj, N., M. Brugger, R. Kwan, and S. Leblanc. "Energy Efficiency Trends in Canada 1990 to 2009." Canadian Public Policy / Analyse De Politiques 35.1 (2009): 1-20. Natural Resources Canada, Dec. 2011. Web.

[5] Bruneau, Joel F. "Greenhouse Gas Intensity in Canada: A Look at Historical Trends." Canadian Public Policy / Analyse De Politiques 35.1 (2009): 1-20. Natural Resources Canada. Web.

[6] "Urban and Rural Areas 2009." UN News Center. United Nations Population Division | Department of Economic and Social Affairs, June 2010. Web.

[7] "Comprehensive Energy Use Database, 1990 to 2011." Governement of Canada, Natural Resources Canada, Energy Sector, Office of Energy Efficiency. Natural Resources Canada, 30 Jan. 2014. Web.

[8] Touchie, Marianne, Kim Pressnail, Russel Richman, and Erin Dixon. "An Innovative Approach to Retrofitting Multi-Unit Residential Buildings Using A Nested Thermal Envelope DesignTM (NTEDTM)." 9th Nordic Symposium on Building Physics. Tampere University of Technology, Tampere. 31 May 2011. Lecture.

[9] Hajat, S., S. Vardoulakis, C. Heaviside, and B. Eggen. "Climate Change Effects on Human Health: Projections of Temperature-related Mortality for the UK during the 2020s, 2050s and 2080s." Journal of Epidemiology & Community Health. N.p., 3 Feb. 2014. Web.

[10] Collins, M., and R. Knutti. "Long-term Climate Change: Projections, Commitments and Irreversibility." Climate Change 2013: The Physical Science Basis 12th ser. (n.d.): 1029-136. Intergovernmental Panel on Climate Change, 2013. Web.

[11] "Technology FAQs." Sage Glass, 2014. Web. 

[12] Styles, G. "The Global Energy Mix Still Depends on Oil and Gas." Pacific Energy Development (PEDEVCO Corp.) Corporate Website. N.p., 26 Sept. 2009. Web. .

[13] "Buenos Aires: Plan for Sustainable Mobility." The C40 Siemens City Climate Leadership Awards. N.p., n.d. Web. .