Research Consistently Shows Building Tall Maximizes Emissions

Deep Dive – Climate Change Series

This is the fifth article in a series that looks at the gap between climate rhetoric and reality in terms of what municipal governments say they are doing versus what they are actually accomplishing. The series compares and contrasts policies and outcomes in Halifax, Nova Scotia with its nearest comparable American neighbor, Portland, Maine.

If you’re wondering why care at all about these two cities, you may like to read a brief overview of the series.

Previously, Part 4 illustrated how it’s possible to make a mockery of climate goals with the widespread demolition of existing human-scale development. Here in Part 5, we look at both the research showing that building tall maximizes emissions and different outcomes in Halifax and Portland regarding high-rise development. Part 6 looks at the research that shows us how high-rise densities can be accommodated with considerably fewer stories using courtyard-type buildings. 

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Climate Friendly High-Rises Do Not Exist

There’s a false belief that high-rise buildings are climate-friendly, but engineers and scientists have known for years this isn’t the case. Studies have consistently shown that the emissions produced and energy consumed during the construction and operational phase of high-rises are far greater than for human-scale buildings. As we’ll see, studies also show that cities can often achieve comparable densities to high rises with far fewer floors using a building type known as a courtyard as illustrated below.

All this ties back to the second key objective of any climate action plan noted in Part 3, namely, to end the practice of erecting high-rise buildings and instead accommodate higher densities with courtyard buildings having considerably lower heights.

In this article, I’d like to do three things. First, I’ll show you what Halifax is doing with high-rises, in light of its climate action plan. Next, we’ll look at the studies. Then I’ll talk about what Portland is doing differently. Before doing any of this, I need to say just a few things about the net-zero movement and high-rise buildings.

The False Promise of Net Zero High-Rises

Climate action plans dutifully refer to “net-zero” buildings. A municipality might say, for example, that by some future date (typically 2050), every building will be a net-zero building. In other words, neither a building’s construction nor its operation would produce a net gain in CO₂ emissions. This is a complex subject that is not the focus of this article. But we can keep one key point in mind regarding net-zero discussions to put what I’m talking about in this article into context. Widespread claims made by developers or local governments suggesting high-rise buildings are sustainable or can be classified as net-zero buildings is, quite simply, greenwashing.

The chart below helps clarify. It was created by ARUP, a British multinational design and engineering firm involved with many high-rises around the globe. What the chart tells us is that as building height increases, so does its “carbon intensity.” Carbon intensity refers to the amount of CO₂ per square meter that’s emitted into the atmosphere in relation to a building’s construction. Let’s look at an example.

On the chart above, you see a 51-story high-rise named 8 Bishopsgate. Completed in 2023, this 51-story high-rise has a gross internal floor area (GIA) of 84,800 square meters. It’s considered as an exemplar of sustainable development. ARUP’s own figures, however, call this claim into question.

For every square meter in the building, 830 kilograms of CO₂ were emitted during the construction phase. This means that just over 70 thousand metric tons of CO₂ (i.e., 70,384,000 kg) got released into the atmosphere before anyone occupied the building. This is the equivalent amount of CO₂ that 4.4 million trees absorb in a year.¹ On top of this are the operational emissions, which, as we’ll see, are significantly greater for high-rises relative to low-rise buildings.  

This particular building stands just over 200 meters tall. The chart below shows all the 200+ meter high rises built each year globally since 1980.

Omitted from the chart are all those thousands of other high-rises built to heights of 20, 30, or 40 stories. Taking these into account, you get a sense of the enormity of the problem regarding the tonnage of CO₂ emitted during the construction phase alone. Here we’re accounting for the manufacturing of steel, cement, and other materials. We often call this CO₂ “embodied carbon.” I like the term “up-front” emissions since it’s clearer that we’re referring to the emissions produced before anyone occupies the building.

ARUP themselves have candidly explained why “up-front” emissions are far greater for high-rise buildings than they are for “low-rise” construction. What follows is a somewhat technical description, but worth digesting.

As buildings become significantly taller, they typically require more structure (thicker core walls, bigger columns, larger foundations, etc.) and more space and equipment associated with vertical movement of people (lifts ad stairs) and building services (risers, interstitial plant provision, etc.). As well as requiring more material and systems, the net-to-gross ratio of tall buildings naturally starts to fall due to the addition of extra vertical circulation provisions and as such there is a double hit when carbon intensity is measured against the effective usable (net) area of the building. Often this can mean an embodied carbon expenditure of more than 50% additional is required to provide the same net useable area between high- and low-rise construction.

ARUP

This is the kind of information that is routinely ignored by government officials. They’ll declare a “climate emergency,” and then march to the drum of a municipal agenda shaped by influential developer interests pushing for more vertical and horizontal urban sprawl.

I’d be remiss if I didn’t acknowledge the use of reinforced timber for high-rises. Over one hundred have been built worldwide. These buildings, however, still require the use of steel and concrete. Experts involved with reinforced timber state emphatically that building towers with timber typically “does not make sense.” Reinforced timber, however, is the perfect material for extending the human-scale city, as is being done in Stockholm on a former industrial site.

There’s more to say about the net-zero movement, but this isn’t the article. I simply want to clarify upfront that there is a global, multi-trillion-dollar industry that’s aware of its environmental impact. It makes sustainability claims and gives out industry awards for “green” high rises. The fact is high-rise construction is a major part of an environmental crisis that goes beyond emissions. Concrete, for example, is the most destructive material on earth.

As we’ll see, studies consistently show high-rises require far more energy to operate than human-scale counterparts.

High-Rise Development in Halifax

Before turning to the studies, let’s look at what Halifax is doing in terms of wide-scale high-rise development. As described in Part 2, the cultures shaping development in Halifax and Portland are very different.

In Portland, a community-based vision shapes development that celebrates the city’s history. The city strives to maintain its character through excellence in design.

Top-down decision-making shapes Halifax. High rates of immigration supercharge real estate and construction. It’s a crude form of economic development that many Canadians seem to have become dependent upon. Despite any wishful thinking, it does not work well, as evidenced by the OECD projecting that Canada will be the worst-performing major advanced economy over the next decade and beyond. Nova Scotia’s GDP per capita is lower than that of Mississippi, the poorest state in the U.S., and there’s a good reason for that.

In the 1990s, Halifax did pursue human-scale development. The city was headed in a similar direction as Portland, with an emphasis on resident quality of life.

With the arrival of an urban planner named Andy Filmore in 2005, the direction changed markedly, and Halifax’s high-rise future began to take shape. Many factors shaped this future, including the loss of political representation, flawed assumptions, and poor planning practices to name a few. It’s a cautionary tale for other municipalities that will be the subject of a separate article.

Have a look at the slide show below. It begins with photos I took back in 2013-14 of an out-of-scale convention center that covers two historic city blocks. Its completion marked the acceleration in building demolitions described in Part 4, as well as the construction of high- and mid-rise buildings across the city.

The image below comes from a larger map of the US and Canada made by a Hong Kong-based skyscraper enthusiast. He’s one of hundreds of young men online who frequently post information about high-rise construction, particularly in Asia and the Middle East. They tend not to talk about environmental or social costs.

What the map is telling us is that in July 2024, Halifax had 33 high-rise buildings under construction. Portland had zero. Keep in mind metro Portland is slightly larger population-wise. This contrast is rooted in cultural differences described in Part 2, which includes a community-based vision in Portland that focuses on quality of life, and quality, human-scale development that reinforces the city’s identity.  

Per the “Top 10” list above, we see Halifax was building more high-rises per capita than any other city in North America. Note that the top nine cities are Canadian. High immigration rates and developer-driven top-down decision-making shape urban planning across Canada.

What’s happening here from a planning perspective is, again, the subject of a future article. My point is to highlight the extreme differences between Portland and Halifax.

With all this in mind, let’s look at four different studies that underscore the degree to which claims made by Halifax to be a “climate leader” are not credible.

Study #1: University College London

University College London (UCL) is the #1 rated school in the world for architecture and the built environment. Between 2015 and 2017, Professor Philip Steadman led a team of six researchers at UCL’s Energy Institute to answer the following two questions:

1. Are high-rise buildings more energy-intensive than low-rise buildings?
2. Is it possible to provide the same floor area on the same site as high-rise buildings, but at a much reduced number of stories?

They found that the answer to both questions was yes. 

Comparing High-Rise and Low-Rise Energy Usage

Steadman’s team assessed the energy usage of 600 commercial and all residential buildings in twelve London boroughs.

As shown below, they found that high-rise office buildings having 20 or more stories consumed two and a half times more electricity per square meter than “low-rise” buildings (6 stories or fewer). Natural gas consumption for heat rose by 40%. And overall carbon emissions doubled.

Unlike office buildings, individual utility bills for private residences were not publicly available. To analyze residential buildings in the twelve London boroughs, Steadman’s team needed a different approach.

They got ahold of publicly available data that provided them with the total amount of electricity and domestic gas supplied to individual census areas. Each census area included between 400 and 1200 households. Additionally, they were able to get public data on building height in those same areas. With the two data sets in hand, the team used regression analysis to determine the relationship between energy usage and building height. Like office buildings, they found that energy usage increased with building height.

Providing Identical Floor Area on Same Site with Reduced Number of Stories

Knowing energy could be saved (and emissions reduced) by constructing low-rise buildings amplified the importance of the second question: could high-rise densities be provided for with low-rise buildings on the same site? The answer to this question is, in most cases, yes. I explain why this is so in the next article in this series (Part 6).

As a preview, let’s have a look again at the figure shown earlier depicting two alternative proposals for a specific site in London. On the left, you see a concept drawing for a 36- and 41-story tower and some 7-story buildings. Steadman and his team showed that the developer could provide the same floor area with an 8-story courtyard building. These findings align with research that goes back to the early 1970s and explains why this is even possible. The information conveyed in ARUP’s quote above is part of the story but there’s more, as I said, to cover in Part 6.

Research Team:

• Philip Steadman—MArch, Emeritus Professor of Urban and Built Form Studies, Energy Institute, Bartlett School of Energy, Environment, and Resources, University College London
• Ian Hamilton—PhD, Energy and the Built Environment
• Homeira Shayesteh—PhD, Architectural and Urban Studies
• Stephen Evans—MSc, GIS & Land Information Management and Mapping
• Graciela Moreno—MArch, Urban Design
• Michael Donn—PhD, Building Sciences
• Daniel Godoy-Shimizu—Research Fellow in Building Physics Modelling at University College London’s Bartlett School of Environment, Energy & Resources

Below are two key Dutch researchers who provided the UCL team with analytic tools relating to providing equivalent floor areas at reduced heights. I’ll also talk more about their work in Part 6.

• Meta Berghauser Pont—PhD, Urbanism (Urban Morphology and Density), MArch (Architectural Theory)
• Per Haupt —PhD, Urban Planning and Design, March

Study #2: Adrian Smith + Gordon Gill Architecture

When complete, the Jeddah Tower will be the tallest building in the world, standing over 1 Km tall. You’d not expect the firm that designed this “supertall” to produce a report definitively showing that high-rise buildings consume more energy and emit more CO2 relative to human-scale development, but that’s precisely the case.

In 2015, the Chicago-based architecture firm, Adrian Smith + Gordon Gill, compared the environmental performance of different building typologies. They ranged from 215-story “supertalls” to single-family houses.

The research team designed a simulation model composed of building typologies. Simulated buildings complied with Chicago’s building codes. The simulated neighborhoods in which buildings sat were derived from GIS data maintained by Chicago and Naperville, Illinois.

To calculate energy consumption, they created energy models using Design Builder and Energy Plus. Both tools are industry standards for profiling energy demand.

To calculate the emissions each building produced, they used data from the Athena Sustainable Materials Institute, the University of Bath Inventory of Carbon and Energy (ICE), and the Concrete Pipeline Systems Association.

As shown below, the study revealed that building at the human scale resulted in the least energy consumption and emissions. Importantly, the results below do not include embodied carbon, which would worsen the difference between building tall and building at the human scale.

Researchers found that high rises (16-story, 34-story, 58-story) have higher operational energy requirements for several reasons, including:

1. Added loads of water pumps (i.e., water needs to be pumped to higher elevations, thus more energy is consumed).
2. Added loads for elevators.
3. Higher loads for cooling, fans, and plug loads.
4. Architecturally, higher glazing ratios perform poorly compared to the high-mass envelopes of human-scale buildings. Reasons include higher infiltration rates in upper stories, heat loss in winter, and unwanted heat gain in summer.
5. Elevators, which account for 10% of total energy consumption for supertalls (i.e., taller than 300 meters) and 4-6% for other high rises.
6. Tall buildings depend on a series of spaces that are not residential units but account for 30% of the total building area. Among these are the mechanical floors, the lobbies and amenities, and parking garages. These spaces are continually illuminated and air-conditioned (or heated) yet are infrequently occupied. (This is essentially the same point that ARUP makes above.)

Research Team:

• Katrina Fernandez—MSc, Environmental Building Design
• Christopher Drew—PhD, Desert Ecology
• Keara Fanning—MSc, Bioenergy

Additional support from the University of Bath:

• Stephen Allen—PhD, Mechanical Engineering (Thermodynamic and Life Cycle Carbon Analysis of Energy Supply for Buildings)
• Craig Jones—PhD, Mechanical Engineering (Thermodynamic and Life Cycle Carbon Analysis of Energy Supply for Buildings)

Study #3: Edinburgh Napier University

Nature and Science are the two most prominent peer-reviewed science journals in the world. In July 2021, Nature published a study by researchers at Edinburgh Napier University titled, Decoupling density from tallness in analysing the life cycle greenhouse gas emissions of cities. The study determined that high-rise operation produces far more emissions than human-scale development. And like the University College London study, it debunks the belief that tall buildings are the most effective solution for accommodating population growth.

The study features 5000 simulated urban environments using real-world data from European cities. Researchers analyzed four urban typologies shown below: a) High Density/High-Rise, b) Low Density/High Rise, c) High-Density/Low-Rise, and d) Low-Density/Low-Rise.

Their research reached two main conclusions. First, High-Density/High-Rise (Figure a) development significantly increases Life Cycle Greenhouse Gas emissions in a way that High-Density/Low-Rise (Figure c) does not. Second, High-Density/Low-Rise urban topologies use land more efficiently. The authors state,

The results of this study suggest that there is no merit to the claim that building denser and taller is more sustainable. By building dense, low-rise urban environments, the same populations can be accommodated for drastically lower carbon costs and without having to significantly increase land use.

Edinburgh Napier University

Research Team:

• Francesco Pomponi—PhD, Life Cycle Assessment
• Jay Arehart—PhD, Architectural Engineering
• Ruth Saint—PhD, Engineering and the Built Environment
• Bernardino D’Amico—PhD, Timber Engineering, Computation and Structural Design
• Niaz Gharavi—PhD, Structural Engineering

Study #4: BC Hydro

BC Hydro is the public utility that provides electricity to residents of Vancouver, British Columbia. In 2019, BC Hydro completed a study that further dispelled the myth that cities grow greener as they grow taller.

For well over a decade, Vancouver has been hailed as a “climate leader” as that city filled the sky with high rises. However, when BC Hydro examined energy usage throughout the city, they determined the city’s reputation as a climate leader was misplaced. And I should add that a lot of this “sustainable” development was paid for with “billions in dirty Chinese cash.”

It turns out that many of the supposedly energy-efficient (i.e., LEED) high rises they’ve been erecting consume significantly more energy than older buildings.

BC Hydro examined energy use across the city and found “electricity used per square foot nearly doubling since for new buildings in comparison to those built in the 1980s.” Their study goes on to say that,

Despite many new, high-end condo buildings being marketed as being energy-efficient, British Columbians living in them have a much larger energy footprint than those living in older condos and apartments–regardless of what they may think.

BC Hydro

BC Hydro notes that units in new high-rise buildings are often marketed as being energy efficient. Yet operational energy goes beyond what’s required by LED lighting and ENERGY STAR® appliances. When analyzing their BC Hydro billing records, they also determined that newer high rises were consuming four times as much energy as low rises built thirty years earlier.

As shown below, the biggest increase in the change of energy usage occurred between 1999 and 2009. Levels have remained elevated since.

As the Adrian Smith + Gordon Gill team noted, 30% of buildings is given over to spaces such as mechanical floors, parking garages, and lobbies. These spaces require heating, cooling, and lighting. BC Hydro has said that much of the increase in energy consumption in newer high rises is related to new kinds of spaces in buildings such as sporadically used pools, workspaces, hot tubs, party rooms, and fitness centers.

Research That Should Shape Development Policy

The next time you hear someone talking about a new, sustainable high-rise project, consider keeping these studies in mind.

The takeaway is straightforward. All research to date consistently shows us that high-rise development produces worse-case outcomes for the climate. A credible climate action plan would acknowledge this fact and establish an objective to reduce emissions by pursuing compelling human-scale development.

As we’ve seen with Halifax, the gap between climate rhetoric and reality can be wide indeed. Portland’s trajectory has been different. Recall that the city had no high-rises under construction when that map above was made in July 2024.

Over the past twenty years, Portland has built just one 18-story high-rise called the Casco. Most everything else has been built at the human scale. Hobson’s Landing on Commercial Street in Portland is one of many good recent examples of the kind of development that aligns with the community vision expressed in Portland’s master plan.

Earlier, in Part 3 I mentioned that there were some risks ahead in Portland as their council recently approved changes to their zoning map which increased height limits in part of the city. I’ll talk more about this in Part 6 when I look at research spanning five decades that consistently shows that in most cases, it’s possible to provide the same floor area as high-rises with a “much-reduced” number of stories. All of this again happens on the same building site.

In the end, all these studies are somewhat meaningless if they’re not given the time of day by local governments making decisions regarding what gets built. There are so many benefits to ending the practice of high-rise development and embracing the human scale. These reasons go beyond emissions when considering what good human habitat entails for our children and ourselves. Talk to your counselor, or better yet, run for office.

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Up Next: Part 6, looks at the research that shows us how high-rise densities can be accommodated with considerably fewer stories using courtyard-type buildings. Previously, Part 4 illustrated how it’s possible to make a mockery of climate goals with the widespread demolition of existing human-scale development.

1. Where the 4.4 million figure comes from? The global reforestation non-profit One Tree Planted has determined that the average tree absorbs 10 kg of CO₂ during the first 20 years of growth. This figure is based on a review of their projects around the world. Other organizations such as European Environment Agency use a less conservative figure of 22 kg for mature trees but do not specify the methodology as does One Tree Planted. For this article, I’m using the mean of the two figures, saying in effect that the average tree absorbs 16 kg (0.016 metric tons) of CO₂ per year. Real world absorption rates are a function of species, location, age and more. So, to absorb the 70,000 metric tons of CO₂ produced during 8 Bishopsgate’s construction phase, you’d need  4.4 million trees growing for one full year (since 70,000 ÷ 0.016 ≈ 4.4 million). ↩︎