Should We Stop Building New Homes?
Housing is key for the economy. But it generates major emissions and uses substantial energy. Reducing cement emissions and using wood helps. Remodeling may be better than new construction.
July 31, 2023
Investors and economists focus on the latest housing data — new home starts, building permits, used and new home sales, and housing vacancy rates — for indications of the health of the real estate sector. Real estate represents 17% of the nation’s Gross domestic product (GDP), but importantly is the foundation of wealth building for the middle class and provides insight into the health of the flow of goods, services, and income for millions of Americans.
The real estate sector produces about 30% of the world’s annual greenhouse gas emissions and consumes nearly 40% of the world’s energy, according to the U.N. Environment Programme. Ten percent of those emissions come from cement, a key building material for world economies. Concrete is the second-most used material in the world after water and it is the most used construction material.
It is estimated we produce about 4 tons of concrete, or just under 60 cubic feet — a cube measuring 4 feet on each side — for each person in the world annually. It represents between 4% and 8% of global emissions. If cement were a country, it would rank fourth in annual carbon emissions.
As the world focuses on decarbonization in addressing climate change, cement and real estate are moving into the target zone, after aviation and shipping. Eliminating carbon emissions from cement is hard, because manufacturing it is highly energy- and emissions-intensive since extreme heat is needed. Emissions come directly from the heating of the limestone that releases carbon dioxide. The burning of fossil fuels to heat the kiln indirectly results in the release of CO2.
Producing a ton of cement requires about 4.7 million BTU of energy because the kilns must be heated to 2,700 degrees Fahrenheit to break down the limestone, which is then mixed with gypsum to make clinkers that are ground up to make cement. The energy needed to heat the kilns is the equivalent of burning 400 pounds of coal, which releases nearly a ton of CO2. One way to cut emissions is to switch the kiln’s fuel source from fossil fuels to renewable electricity, but that can be a challenge because of the energy density of coal that allows it to burn extremely hot and the level of heat needed.
In Greece, the government is working on a plan to switch kilns from coal to renewable electricity. The problem, according to the owner of the nation’s largest cement manufacturer, is that amount of renewable energy currently available is insufficient to power all his kilns, let alone any of those of his competitors.
Therefore, the government is trying to ramp up investment in new renewable energy plants. However, because renewable energy is part-time, the grid is susceptible to brownouts and blackouts. The cement company’s CEO said the loss of power for 4 hours will destroy a kiln. To protect his kilns, he is contracting backup power to the supply he receives from the electric company because he expects more outages. This becomes expensive insurance, which will force him to raise the price of his cement.
Cement companies worried about the destruction of their kilns from blackouts have few alternatives other than independently securing backup power or praying a lot. Could there be other solutions to cement’s emissions problem? Are there ways to make the process more efficient, such as improving how kilns work Maybe cement can be made from lower-carbon raw materials, or produced differently, such that when blended with the other necessary materials it will still make a product equal to traditional concrete.
Major cement companies are experimenting with different mixtures of limestone and gypsum to reduce the energy needed to turn it into a cement-like product. Startups, often founded by material sciences professors at major research universities, are testing many of these solutions. Some of these companies are also exploring other solutions.
C-Crete Technologies says it has invented a new process that does away with cement entirely in making concrete. The product utilizes a mixture of natural minerals and industrial by-products. In its manufacture, it produces almost no carbon dioxide. It also absorbs CO2 from the air over time. But will it stand up to the long-term performance of traditional concrete?
The company says that each ton of C-Crete binder-replacing cement prevents about a ton of CO2 emissions. In a recent press release, C-Crete said the product was used for the first time in a foundation and sheer walls of a commercial building being built in Seattle.
Another startup, Chement, based in Illinois, has invented a way to make cement at room temperature. Although the process still produces CO2, it avoids using kilns heated by burning coal and powers its process with renewable energy. The emissions released are in the form of a pure gas that can be captured. The cost of carbon capture in such a plant is estimated to be a small fraction of trapping those emissions from existing kilns.
While these startups offer promising ways to reduce cement emissions, they are in their infancy. We don’t know their economics at scale or the long-term performance of their output, but they are promising.
When we turn to the issue of emissions from the real estate sector, two interesting trends are emerging. The first is the return of wood as a construction material, even for high-rise hotels, apartments, and office buildings. Known as “mass timber” construction, it utilizes trees selectively cut rather than clear-cut. Therefore, building with mass timber creates less waste, can be quicker, and can be quieter than using conventional construction materials.
The tallest mass timber building is the 25-story Ascent MKE apartment building in Milwaukee that stands 284 feet tall. It features 259 luxury apartments, retail space, an elevated pool with operable window walls, and a sky deck.
These are not log cabins or even stick-built homes, these high-rise buildings use cross-laminated timber. That is essentially large-scale plywood, made by gluing two-by-fours together into a sheet, then flipping the sheet 90 degrees and gluing more two-by-fours on top. This produces a sheet of wood that is much like a slab of concrete but weighs 80% less. The wood is kiln-dried, a process that can take weeks, but the manufacturing process enables computer imaging to cut pieces precisely to size before they are transported to the building site, which reduces construction time.
To replace steel, glue-laminated timber can be made to resemble beams rather than sheets. These beams can support buildings, and they can be bent allowing design options such as domes.
Challenges in building with mass timber are moisture content and building strength. The timber must be dried to the normal moisture environment at the building’s location. If it is too dry, then the structure will absorb moisture and swell. Likewise, if there is too much moisture, it can dry out and crack. In either case, there would be structural issues. Since mass timber is manufactured in a plant, its moisture content should be able to be managed sufficiently to avoid these structural issues.
Wood, though, does have a strength problem. It is lighter than steel and concrete, which means fewer piles are needed to support a foundation, or the concrete slab it is built on can be thinner, but the challenge becomes as the structure gets taller. Steel with concrete coatings adds strength to the structure, which does not happen with wood. Since tall buildings must be able to sway to compensate for wind and earth movements, a building that sways too much or too fast will make its residents or office workers seasick from the motion.
Therefore, wooden structures must take stiffening measures to reduce the potential swaying from the lighter material. This is more of an engineering issue and not a safety issue.
Another drawback to wood construction is that it is a resonant material. This requires adding sound-deadening material to the walls to dampen the sound-transmission quality of wood. Again, an easily addressed issue, but the additional cost will offset some of the savings from the speed of wood construction compared to building with steel and concrete.
While key construction materials are changing to adjust to a decarbonized world, there are other interesting emissions reduction trends emerging in residential and commercial construction markets. The trends were described as “the carbon conundrum” in a recent Financial Times article, which discussed new home construction versus renovation from the viewpoint of climate change.
The debate centers on the focus of most homebuyers interested only in the operational carbon emissions of their new home rather than the embodied carbon in the materials used for its construction. This can make renovating an older home that uses fewer new materials the more environmentally friendly choice.
The Financial Times article detailed the purchase and renovation of a home rather than the expected teardown and rebuild. Catherine Ramsden, who runs an architecture and design practice, bought a “well-appointed 1960s family home in the countryside near Surrey’s Box Hill” that she then preceded to renovate as opposed to the widely expected tear down and rebuild.
By converting the garage into living space, she expanded the livable area by a third to 3,165 square feet. She estimated the CO2 savings compared to building a new home of that size was 86 tons or 21 years’ worth of emissions from running the average U.K. home.
According to architects, engineers, and sustainability consultants the Financial Times spoke with, customers are fixated on the carbon emissions generated by operating their homes while ignoring those created by construction. Cador Pricejones of Byggmeister, a Boston-based design and building company that specializes in remodeling and retrofitting existing homes, told the Financial Tines, “I would love to say that embedded carbon is why people are coming through our door, but I can’t. What is motivating most of them is to get off natural gas and electrify their homes.”
The problem, as the article noted, is that “the emissions generated by construction materials are already released into the atmosphere, whereas those saved incrementally by using a heat pump or by improving insulation take decades to accrue.” That is like the emissions generated from building an electric vehicle versus driving it carbon-free. It takes years of driving to offset the legacy emissions.
We found a comment attributed to an engineer about energy efficiency in the Financial Times article interesting. “When it comes to energy efficiency [on appliances], everything is labelled,” said Jesus Menendez, an engineer working in the United Kingdom and Spain. “Why not put a label on [showing] the carbon that was used to make it?”
Since we believe education is the best way to motivate the public to change their consumption patterns, why not label appliances and even electric vehicles with the data about the carbon emissions generated when they are being made? The labels could show both the emissions created and those avoided by their use.
If we are so concerned about stopping the amount of carbon emissions we are putting into the atmosphere, we suspect people would be surprised to see how much is released when products are made versus how long it may take in using them to offset those legacy emissions. Maybe consumption patterns would change, but maybe they would change in the wrong direction as consumers weigh the cost/benefit of purchase and construction decisions.
Houston resident Allen Brooks, a summer/early fall inhabitant of Rhode Island for the past 26 years, has been publishing the Energy Musing (formerly called Musings From the Oil Patch) newsletter since 1999. To sign up for his newsletter, click here.