In addition to building codes that are legally required and enforced by inspectors, there are a few new sets of standards that are entirely voluntary, mainly to promote “green buildings.” Those standards are generally higher than the mandatory codes maintained by governments, though they often are invoked to improve usual practices. One such voluntary code is that developed by the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) (3), but probably the best-known code is LEED, which is run by the US Green Building Council.

LEED stands for “Leadership in Energy and Environmental Design,” and it regularly updates its checklists of standards for architects and engineers working at the planning stage, before construction begins. Professional designers can apply (and pay a hefty fee) to have their plans ranked according to four levels of excellence: certified, silver, gold, and platinum. The idea is to produce buildings that “maximize occupant health and productivity, use fewer resources, reduce waste and negative environmental impacts, and decrease life cycle costs.”(4) The most important goal of such “green” design is to reduce the use of energy in each planned building and thereby reduce the emission of greenhouse gases. Buildings that are certified as green often sell for a premium price and garner praise for their architects.

But it is no simple matter to construct greener buildings around the world, and actual progress has been disappointing, as The Economist pointed out in a January 2019 issue. Its article is bluntly titled, “Efforts to Make Buildings Greener Are Not Working.”(5)

This shortfall even applies to the zealously committed LEED people. Their buildings are certified early – during the planning stage- and are not inspected after the construction is complete. If someone does check on the outcome later, she may see a wide disparity between the high original intentions and any real reductions in greenhouse gas emissions or the use of energy. Along the way, less expensive materials are often substituted for the ones originally specified. By now it has become evident that standards need to be tightened up globally and somehow enforced.

Sometimes the architects and engineers are themselves to blame for this discrepancy. For example, the LEED appraisal process assigns points to a proposed new building if it will reduce the use of electricity. However, the LEED accounting scheme does not include the electricity that will be drawn from wall plugs. Hence, in order to make her plan look good, an architect may plan for fewer built-in lighting fixtures and expect that lamps will be used instead. Of course, this means that there will be no real savings in the end, even if the building had been given high points for “greenness.”

But when a government enacts a building code, there will be real inspections and enforcement mechanisms, and so there is an increasing demand for tighter environmental standards to be legislatively adopted and legally enforced.

But, for two reasons, this has not helped matters much so far. First, building codes only are relevant to new buildings or to old buildings being renovated. Only about one percent of all buildings are replaced each year, so few houses and commercial buildings will be required to improve. This is no way to make quick progress worldwide.

Second, enacting legislation for tough new regulations is a political issue, and it will almost always encounter opposition. This is inevitable, since there will usually be start-up costs involved in the change, even if everyone can expect to benefit financially in the end from it. Carbon taxation is a case in point.

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The best way to reduce the consumption of energy is not to change the building codes but simply to tax heavily the carbon in fuel. Unfortunately, the consumer can see the higher price every time she refills her heating oil tank or pays her gas bill. Even when governments promise to refund all the carbon tax money to households or spend it on greater services for the working class, such legislation will be opposed and maybe defeated. Voters seem more amenable to toughening up the building code and adding the extra costs onto the selling price of the building. But again, that only applies to new buildings and to old ones being refurbished.

And there is another explanation for the slow progress toward greening the world’s buildings: Banks normally only pay to upgrade one thing at a time, such as installing insulation. But it would be better to retrofit a whole house at once, including by adding digital thermostats to lower the use of energy.(6)

Thus, it seems that progress has been too slow, so building codes and other basic principles have to be pushed harder. But what are the most promising changes to promote? Let’s consider, first, some basic principles and then some of the choices of building materials that matter.

Density Versus Affluence?

Let’s celebrate two of the greatest events going on in the world today: urbanization and the end of poverty. The interesting thing is that they are both connected to the climate crisis, but not in the way we’d prefer.

The world is urbanizing. By the year 2050 it is expected that there will be 9 billion people on this planet and that 70 percent of them will live in densely concentrated urban areas.(7) Moreover, today less them 10 percent of the world population lives in poverty, whereas in 1990 the corresponding figure was about 37 percent. Two centuries ago almost everyone in the world lived in extreme poverty.(8) We are ending poverty.

How does this happen? Poor people are gravitating to towns and cities, where they take advantage of the greater economic opportunities and soon improve their standards of living. A World Bank report shows that “poverty in rural areas is markedly higher than in urban areas, even though the urban poor have a higher cost of living.”(9)

Hurray for urbanization? Well, yes and no. Yes, for its effect on poverty, but no when it comes to the overcoming the climate crisis. Poor people everywhere emit less greenhouse gas than rich people, but when poor rural people migrate to the cities and become more affluent, they also join the rest of us in putting more carbon into the atmosphere.(10)

Overall, cities seem to worsen climate change. According to UN Habitat, cities consume 78 per cent of the world’s energy and produce more than 60 per cent of greenhouse gas emissions. Yet, they account for less than 2 per cent of the Earth’s surface.(11) Indeed, the trend is growing. By 2030, urban areas are expected to account for 76 percent of energy-related global greenhouse gases.(12)

Logically, this contradicts another well-established fact: that density is a major solution for the problems of global warming. Indeed, on a per capita basis, urban residents generate considerably less carbon emissions than rural people in the same country. There are many advantages to living close together.

How so? Cities concentrate people and economic activities. This makes possible economies of scale and greater efficiencies in energy use. Because they live near businesses, city dwellers are more likely to walk, ride their bikes, or take buses and subways rather than drive their cars and emit carbon from the tailpipes. Gasoline use per capita declines with urban density, and it is cheaper and more efficient to heat and provide electricity to high-rise apartments than separate houses.

Indeed, urban density should be a top priority for anyone planning sustainable construction. That is why realtors say that the top three priorities for buildings are “location, location, and location.” Dense locations are best. As the writer David Owen pointed out when criticizing Gap, Inc for building a marvelous new building in San Bruno, California. It was beautifully designed with all kinds of environmentally friendly features, but it was 15 miles from the company’s headquarters in San Francisco, and 15 miles from its other plant in Mission Bay. The location forced Gap employees to drive long distances, so the company added shuttle buses. But as Owen points out, “no bus is as green as an elevator.”(13)

So, if urban density tends to reduce carbon emissions, why do cities account for too much greenhouse gas? When you compare rural and urban people of the same income level, you’ll find that city-dwellers almost always use less energy and emit less greenhouse gas than rural people. But rural and urban people don’t actually have the same income levels. City dwelling typically makes people richer, and rich people tend to produce too much greenhouse gas, no matter where they live.

Research seems to confirm this explanation. Not all urban districts emit equal amounts of greenhouse gas. The suburbs, with their monster-size houses, vast lawns, and three-car garages are the worst offenders. And even neighborhoods of modest single-family houses are far worse than clusters of high-rise apartment buildings. The least amount of carbon is emitted in crowded areas, including high-rise slums.

The same factors partly explain why cities vary so much in their impact on the climate. For example, Denver residents emit twice as much CO₂ as New Yorkers, mainly because of New York’s greater density and lesser need to commute by car.(14) Cities that include large industrial areas or airports account for more carbon emissions than cities where a large proportion of the inhabitants work in “knowledge” jobs.

Still, neither density nor affluence explains all of the variation between cities’ emission levels. A more adequate explanation takes account of the differences between emissions caused by production and those caused by consumption . Many of the activities that produce and emit carbon can be located far outside of towns, whereas it is cities that consume their products. Take electricity, for example. Hydroelectric dams, coal-fired plants, and nuclear power plants are located in rural areas, but most consumption of electric power occurs in urban areas. Likewise, farms produce much of the carbon and nitrous oxide in the air, but they do so to produce food for city-dwellers to eat.(15) And some cities are primarily consumers of CO₂-generating products, whereas industrial cities are mainly the producers.

There is a wise old saying that people should be responsible for cleaning up their own messes instead of putting the burden onto others as “externalities.” However, if we want to assign responsibility (or blame) for greenhouse gas emissions, who should have to clean up the mess – the (often rural) producers or the (often urban) consumers? Actually, like it or not, we all do. It’s our mess now.

Fortunately, there are some general principles that, if observed, can make cities greener. These are not necessarily covered by building codes but can be part of a city’s overall plan. One simple principle is just to build spaces no larger than necessary. If we want density, we cannot have “urban sprawl,” or even gigantic houses that use immense amounts of energy. Zoning regulations can help to limit the size of housing units. Besides, mansions are passé. Buy a condo downtown instead and have more fun.

Second, we can strategize ways of cooling urban “heat islands” – the areas in a city where hot buildings and pavements have replaced cool, permeable soil and vegetation. A city of one million people can be 1-3°C warmer than its surroundings(16) and on a clear, calm night, the temperature difference can be as much as 12°C.(17) We need to plant far more trees, shrubs, and rooftop gardens to counteract such heat islands.

Much of the heat island differential can be attributed to the “albedo effect” – the reflection of light (and therefore heat) back into space from white or pale-colored surfaces, and the absorption of light (and therefore heat) by dark surfaces. This fact gives us a solution: paint roofs white, or pave with pale beige concrete instead of black asphalt. There are some disadvantages to this, however: Concrete sidewalks and roads can be more slippery with ice in the winter than asphalt, and the pale pavement can reflect heat onto nearby buildings, whose inhabitants may have to use more air conditioning, which defeats your purpose.

Ordinary pavements also have another disadvantage when it comes to water-retention. Concrete and asphalt are hard, impermeable surfaces. When it rains, the water must run off into sewers and conduits, where it is wasted or sometimes overflows and becomes a flood.

Lately good solutions have been developed for this problem: permeable blocks of cement that can allow stormwater to seep through into the soil below, or at least can be set far enough apart to allow water to flow through the cracks and return to the groundwater.(18) This is not an adequate solution for roads that must support heavy traffic, for their structure must be strong, but it works well for many sidewalks and patios, cooling the environment somewhat and reducing the risk of floods.

Sustainable Building Materials

As noted above, the construction industry has not progressed far in reducing carbon pollution in their new buildings. This shortcoming has to be attributed largely to the fact that three of the main building materials – steel, concrete, and glass – are still large sources of carbon emissions. Though manufacturers are seeking solutions to these problems, none are very satisfactory yet.

To be sure, there are some novel ideas for materials to be used in buildings: These include straw bales; bamboo; recycled plastic or sawdust mixed into concrete; rammed earth; and ferrock, a mixture of recycled materials such as steel dust, which absorbs carbon dioxide when it dries, thus being actually a carbon-neutral substance instead of emitting CO₂. But major improvements in materials are disappointingly slow to arrive. Iron and steel account for 24 percent of the building industry’s emissions and concrete accounts for 18 percent.

Steel

For at least 150 years the method of making steel has not changed much. Iron is put into large blast furnace with coke, a fuel made from coal, and this turns the iron ore into liquid metal, which is then refined into steel. Inevitably, carbon dioxide is in the output, though it is possible to reduce the quantity of it by using scrap metal and electric arc furnaces instead of raw iron ore and by omitting the coke. Unfortunately, there is not enough scrap metal for this to help much.(19) The Indian manufacturer Tata Steel Europe is working on a method of reducing both CO₂ emissions and energy consumption by one-fifth, but that modest improvement is not likely to be used commercially until at least the 2030s. The delay is caused by the technical difficulties. The most promising possibility is to eliminate carbon emissions from the ironmaking stage by using hydrogen, though then there will be a problem obtaining the hydrogen. It can be produced by electrolysis, but in the end, such steel will cost more.(20)

At present, steel is widely considered essential for the structural frames of tall buildings, but it does present certain challenges for the engineers and architectural planners. Steel conducts heat very well, which is sometimes an advantage but often not. When high-rise apartment buildings are being retrofitted to reduce energy use, the balconies present a special problem. The steel beams that support the whole building generally protrude outward, supporting each balcony, and in doing so they transfer heat out and waste it. If these balconies are to become “green,” their support must somehow be detached from the steel beams, so they do not waste heat.(21)

Concrete

Concrete has a long and wonderful history. It was apparently used more than 8,000 years ago in Jordan, to create floors, buildings, and underground cisterns. The Pantheon in Rome remains to this day the largest unsupported concrete dome in the world. Roman concrete was based on a hydraulic-setting cement. It is stronger and more durable than our modern product because it contained volcanic ash, which prevents cracks from spreading.(22)

Concrete is still used everywhere. According to a BBC report, “production has increased more than thirtyfold since 1950 and almost fourfold since 1990. China used more concrete between 2011 and 2013 than the US did in the entire 20th Century,” and concrete production is expected to increase by a quarter by 2030.(23)

Unfortunately, concrete also contributes more CO₂ to the climate crisis than aviation fuel. One ton of concrete production produces a ton of CO2 emissions, and with 5 to 7 percent of the world’s carbon emissions emanating from its production,(24) it presents us with a problem in urgent need of a solution.

Concrete is made of Portland cement, water, and aggregate (rock, sand, or gravel). The Portland cement itself is made from crushed limestone and aluminosilicate clay, which are heated together in a huge kiln at about 2,640 degrees Fahrenheit. The heat splits the limestone’s calcium carbonate in two – creating calcium oxide, the lime content, and carbon dioxide, the waste that is causing so much trouble to the world today. The product at the end of the cooking is called “clinker,” which is cooled, mixed with gypsum, and ground into powder-the cement. This process is called “decarbonizing limestone,” and it is the source of about 60 percent of the emissions. The remaining 40 percent comes from other processes using energy to manufacture the concrete.

To make concrete, the Portland cement is mixed with water to form a paste, which is then combined with aggregate. This mushy substance is placed into forms, where it dries and hardens into a rock.

Most concrete nowadays also contains fly ash, a fine powder that is a by-product of burning pulverized coal in electric generation power plants. When combined with lime, fly ash can be used as a substitute for some of the Portland cement, and in fact improves the quality of the final concrete. It is generally stronger than the type made only with Portland cement and, like the Romans’ volcanic ash, it reduces crack problems. Its main advantage is that, by replacing some of the Portland cement, the fly ash reduces CO₂ emissions.(25)

Unfortunately, this is not a huge improvement, since the fly ash itself is a by-product of coal-fired power plants-which are themselves probably the worst sources of CO₂, and top priority for environmentalists to close down. Moreover, because it is produced by burning coal, about 15 tons of carbon dioxide is emitted for each ton of fly ash produced. That means that the use of fly ash in concrete can offset only five percent of those emissions.(26) That is better than nothing, so long as coal is being used anyway, but the goal must be to replace quickly both coal use and Portland cement with the better materials.

And there has been progress toward that goal recently. The most promising substitute for the current method of producing cement is a type of “slag cement,” developed by Drexel University engineers. It is activated by alkali – an industrial by-product called slag-plus limestone, and its production does not require heating. The ingredients are abundant and cheap, so the new Drexel cement costs about 40 percent less than Portland cement and reduces energy consumption and carbon dioxide production by 97 percent. It is apparently as strong as Portland cement.(27)

Glass

The manufacture of glass is a simple process. It involves heating ordinary sand (which is mostly silicon dioxide) at about 1700 degrees C until it melts and turns into a liquid. A certain amount of carbon dioxide is released in the process, and more CO₂ is also generated by creating the electricity used for heating the silicon. We need to reduce those sources of carbon emission, which can be achieved to some degree by increasing the proportion of recycled glass used in place of raw materials. However, this improvement is limited by the availability of recyclable glass of acceptable quality.(28)

Still, the problem that building designers face with glass it not so much the production of waste CO₂ during production as its poor performance as insulation against the transfer of heat. A major source of heat loss from a building is through its windows. The best available solution is double glazing of the windows – or even triple glazing. Two or three panels of glass are put into a frame, separated by a vacuum or gas-filled space to reduce the transfer of heat. Still, although floor-to-ceiling windows are attractive to buyers of new modern homes and condos, architects who aim for sustainability are far less enthusiastic about them, since windows pose, at best, a major challenge for the conservation of energy.

Most new office towers are covered with glass and they too present problems for the architect. However, those buildings have an advantage over private homes and condos: The glass sheath covering the exterior of the building is usually a “curtain wall,” which is non-structural. It is separate from the interior part of the building, being hung outside of the concrete slab, using anchors. Curtain walls are self-supporting and give a building’s exterior the look of top-to-bottom glass, admitting light. Condos are built with a “window wall” that is sandwiched between the concrete floor slabs, allowing the uninsulated floor slabs to thermally-bridge to the exterior. Because they consist of a single unit, curtain walls are superior to the window walls of most condo residences in their resistance to moisture, wind, earthquakes, and the transfer of heat.(29)

Wood

At last we come to a building material that everyone can love: wood. Many current green building projects -both new construction and renovations – are using wood. Trees grow naturally, using energy from the sun, and wood is sustainable, renewable, and recyclable. While wood is growing in the wood factory, or forest, trees draw down carbon from the atmosphere through photosynthesis, and emit oxygen – not a bad form of ‘pollution’.

Wood is an effective insulator that requires far less energy to produce than concrete or steel. So long as wood is in use for buildings and furniture, it is keeping the CO₂ locked up that it originally captured from the air. If the wood is burned or allowed to rot in the forest, that carbon will return to the atmosphere. So, use wood for buildings!

Smaller pieces of wood can be laminated together to make thick prefabricated slabs-that can be cut into columns, beams, and panels-called “mass timber,” to replace much of the steel or concrete in the structures of high-rise buildings. For example, there is an 1 8-storey mass timber hybrid student residence building at the University of British Columbia.(30) Many more towers are being planned, though the public still has to be convinced that they are safe.

In a video conversation Paul Dowsett and Michael Yorke argued in favor of using wood as structural members for large buildings.(31) They addressed first the question of fire, which is the objection that initially occurs to most people. Wood is, of course, famously flammable. However, when a thick slab of wood is in a fire, the exterior half inch will char, but the interior part will retain its structural integrity, protected by the created layer of char. It compares favorably with steel in allowing the inhabitants of a tall building enough time to escape.

Finally, there is a concern about cutting down trees at the very time when forests are most needed as carbon sinks. We need lots of trees absorbing carbon from the atmosphere and storing it in their trunks, roots, and leaves. Indeed, the most feasible means of reducing global warming probably is to plant about a trillion fast-growing trees in suitable locations and to nurture them to maturity. Cutting timber would seem to be a gross threat to the best method of preserving our planet.

Yes, but that notion should be qualified. Trees are at their most active phase of sequestering carbon while they are young and growing fast. Many trees slow down their carbon intake when they reach maturity, though they do still serve as reservoirs, containing it until they finally fall over and rot, releasing the carbon back into the atmosphere.

Harvested at the right time, trees can be used for building materials, and immediately replaced in the forest by other fast-growing saplings. This practice, if done properly, can be sustainable – more beneficial to solving the climate crisis than by relying on any of the other main building materials that we have discussed. You can expect to see many new sustainable buildings constructed of wood over the next few years. Now let’s celebrate!

Footnotes for this article can be seen at the Footnotes 2 page on this website (link will open in a new page).