Is the greenest building really the one that already exists? Maybe. A report from the U.S. National Trust for Historic Preservation learned through a series of case studies that it takes at least a decade for a new building that’s 30 percent more energy efficient than an existing structure to overcome the negative environmental impacts related to construction. The report concluded that upgrading an existing building for energy efficiency is almost always the best choice, regardless of building type or climate.
It’s true that many commercial buildings will need deep retrofits to meet the industry’s net-zero goals by 2050. But the reality is not all existing buildings can be kept standing. For one thing, the dynamics of the commercial real estate market push developers for new construction. Developers often have pressure to capitalize on the high value of land in big markets like New York City to tear down aging buildings and build taller ones, like ultra-energy-efficient (and lucrative) skyscrapers.
Some older building stock also shouldn’t be kept around for a number of reasons. Aging buildings can become functionally obsolete and may not be designed for the long haul. Highly valuable skyscrapers like the Empire State Building, which opened in 1931, could feasibly last for another century or longer if you factor in renovations and maintenance. The structural integrity of the Empire State is famously sound, made of concrete reinforced with steel. This gives ‘The World’s Most Famous Building,’ and other skyscrapers built in that era, a strength that can resist stretching and squeezing forces and last for a very long time. The primary threat to the Empire State isn’t that it’ll fall apart, it’s that it will no longer have a market of companies willing to lease space in it.
The perception in the real estate industry is that demolishing an aging property and building a new one is always the easiest option. The problem with this is that construction and demolition have an enormous negative impact on the environment. Construction and demolition waste accounts for up to 40 of the nation’s total waste stream. America generated 600 million tons of construction waste in 2018 alone, and 90 percent of that debris was from demolition. Construction and demolition are also among the biggest users of the planet’s raw materials.
Waste is not the only problem. Known as embodied carbon, the construction and demolition of buildings account for 11 percent of the world’s carbon footprint. This stems from the mining, manufacturing, installation, transportation, and disposal of building materials. There’s a lack of standards in the U.S. for measuring and evaluating embodied carbon, though this is starting to change. The push to address embodied carbon is gaining steam in commercial real estate, and part of the solution involves re-thinking the traditional demolition process.
A million little pieces
Several solutions have been proposed to tackle real estate’s embodied carbon and waste problems. Some pioneering architects, engineers, and developers are urging recycling as much of old buildings as possible and creating a circular building materials economy. Others are adapting old buildings for new uses, such as the push to convert empty offices into housing in many cities. A recent project in Australia that I reported on entirely re-imagined a skyscraper without tearing down the original structure.
A related idea emerging is the intentional design of commercial buildings for deconstruction. This concept also relies on the concept of salvaging building materials meaning that valuable materials that are removed intact can be reused in other construction projects. During this process, workers sort materials that can be reused instead of sent to a landfill. The environmental benefits are obvious, including extending the life of materials and avoiding the carbon-intensive process of creating more concrete and steel.
A recent example of a building designed for deconstruction is the new W.A. Franke College of Forestry and Conservation building at the University of Montana. The 70,000-square-foot facility uses cross-laminated timber instead of concrete or steel in its structural system. Wood sequesters carbon dioxide, and the longer it’s in service, the longer the carbon will be seized. Designing the mass timber building for deconstruction ideally means a longer service life for the wood and a more extended carbon sequestration period.
Most mass timber projects have concrete toppings on each floor to add compressive strength, but this project won’t. The architectural firm on the project, HDR, says they skipped the concrete toppings because once you do that, it binds to the wood assembly and makes it harder to reuse in the future. The timber structural elements will also be mechanically connected, which makes their assembly reversible.
The building may use dowel-laminated timber, where layers of wood are attached together with dowels instead of glue or nails. This makes the wood easier to work with during deconstruction and avoids health issues related to adhesives. Cross-laminated timber is easier to reuse than steel or concrete structural systems. Most mass timber is shaped via numerical control machines down to the tiniest of tolerances, so it’s easy to take raw wood back to the machine to reshape it with minimal waste. The building’s reversible mechanical connections could also prove useful if parts must be replaced due to structural leaks. The plan is that one day when the building has overstayed its welcome, it can be carefully taken apart instead of demolished.
Challenges of coming undone
The University of Montana building is just one example of the push for deconstructable designs. Architects say that designing for disassembly is mainly about the materials that are selected, such as durable ones that can withstand the process of building and “construction in reverse.” Some architectural firms are creating deconstruction manuals that would help future building owners complete the jobs safely and efficiently. Structural systems are also designed simply by making all beams one standard size instead of complex composites that combine more than one material type.
Melissa Wackerle, Sustainability Strategist at the American Institute of Architects, wrote a white paper on this topic, and she told me there’s surging interest among architects in designing for deconstruction, along with designing for adaptability and re-use. She said it’s important to note, though, that many places in the U.S. don’t necessarily have a robust marketplace for salvaged building materials. “There have been some attempts on a local level, but there’s a real opportunity to have more of this,” Wackerle said. “We’re really just starting to grapple with this issue.” There’s a small ‘underground’ market of salvageable materials for residential projects in many U.S. cities, but not necessarily for commercial projects.
Portland, Oregon, recently became one of the first U.S. municipalities to pass an ordinance requiring certain residential homes to be deconstructed rather than demolished. More cities are considering similar rules, but there are challenges in making it more of a reality for commercial real estate. Using salvaged materials in commercial projects typically wouldn’t save money if the materials have to be refurbished. There could also be liability issues, as older materials may not adhere to newer building codes. As for existing buildings, deconstruction may not work because many older properties are made from composite materials that are difficult to take apart.
Designing for deconstruction is much more environmentally friendly than traditional demolition. The fact that the American Institute of Architects has published an extensive white paper about the topic means that it’s being taken seriously, but it will take time to catch on. Developing a salvageable building materials marketplace will help, but construction firms must also be prodded into adopting the practice. Many contractors work under tight profit margins and may not be willing to expand into deconstruction along with traditional demolition. Demolition is quicker, cheaper, and easier.
If the real estate industry wants to achieve net-zero carbon emissions, the negative impacts of demolition will have to be factored in. Sustainability efforts in the built world are expanding beyond operational emissions to embodied carbon, and the movement of designing for deconstruction is part of this trend. This practice may not be the standard now, but given time, it could become more widespread, and the end life of more buildings could look much different.
