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Multifamily Trends - March/April 2007 - Point of View

The embodied energy in existing buildings is often overlooked in efforts to encourage energy-efficient construction.

Out with the New and in with the Old

by John McIlwain and Knox McIlwain

In a report published in 2004 by the Washington, D.C.–based Brookings Institution, Arthur C. Nelson of the Metropolitan Institute at Virginia Tech paints a portrait of the United States’ future landscape: “In 2030, about half of the buildings in which Americans live, work, and shop will have been built after 2000.”

This means, of course, that half of all structures that will be standing in 2030 have already been erected, a fact that has profound implications for everyone concerned with sustainable development. In fact, how we use and reuse the existing built environment may affect our overall energy use and our ability to respond to global warming as much as everything we construct new in the years to come.

Nelson estimates that of the roughly 296 billion square feet (27.5 billion sq m) in existence in 2000, 82 billion square feet (7.6 billion sq m)—or 28 percent of that space—is likely to be torn down and replaced. This leaves 214 billion square feet (19.8 billion sq m) of space existing today that still will be in use in 2030, which is equivalent to the 213 billion square feet (19.7 billion sq m) of new space that Nelson estimates will be built during the same period.

This raises two issues: first, what do we do with the space in existence today—how do we make it more energy efficient? Second, how do we reduce the amount of space that is torn down and disposed of, an inherently wasteful activity in many cases?

While most planners, developers, and “green” builders are focused largely on new construction, these two questions about existing space are equally important. The choices we make about what is already built—how we choose the structures to save and how we rehabilitate them—are just as critical to constructing a sustainable environment as all the decisions we make about building new. These choices, however, have received far too little attention to date.

There is an old saying in Maine: “Use it up, fix it up, and wear it out.” Some of the state’s residents actually live by this credo, a reason perhaps why the Maine character is so resilient. Most of us, of course, find this a hard course to follow and one that, were it widely adhered to, might bring the U.S. economy to a sudden, unhappy halt.

When it comes to the built environment, however, the reuse of existing structures intuitively seems more environmentally friendly than demolition and new construction or greenfield development. And it turns out that this hunch is largely correct—the benefits in energy use, raw materials conservation, and landfill savings of reusing existing buildings are like the benefits of recycling household garbage, now a widely accepted practice.

Environmental Advantages of Building Reuse

“[T]he first guideline for sustainability is: use what already exists. When you start from scratch, you can achieve environmental efficiency, but it’s more sustainable to adapt existing buildings and how we live in them,” wrote François Jegou and Ezio Manzini in a 2004 issue of Dwell magazine.

Studies of the environmental benefits inherent in building reuse are few and far between, and many are out of date. More work needs to be done by both academics and industry groups like the U.S. Green Building Council (USGBC) and the Atlanta-based American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) to fully document these benefits. Without better metrics and models, it is harder to determine when a building should be reused, and when it makes more sense to start anew with a high-performance structure.

That said, there is enough information to show that building reuse—under the right circumstances—is environmentally preferable to new construction. This, of course, is different from a determination of whether the reuse of a structure is economically preferable.

There is much to be gained environmentally from reusing structures. One of the most significant benefits is that it does not use new land; building reuse concentrates development where it already exists, thus preserving greenfields and undeveloped land. Moreover, reusing buildings lessens demand for new materials. Similarly, building reuse eases the strain on landfills, reducing the amount of material deposited in them. Furthermore, many older structures were developed using what are now considered “green” techniques or materials. For example, older buildings were often made from local stone, which has a low level of embodied energy, is highly durable, and has good thermal characteristics. And they tended to rely on natural daylight to illuminate the interiors—a technique recently “discovered” in the attempt to build greener. To make natural daylighting effective, older edifices typically have deep reveals or awnings, features that allow light to enter, but which shield the interior from direct sunshine during the hot summer months, making cooling easier. In addition, many older buildings employ operable windows as a solution to temperature regulation—another technique recently rediscovered.

But the biggest savings to the environment to be derived from reusing existing buildings is the amount of embodied energy their reuse saves.

Embodied Energy

Embodied energy is the “the sum of all the energy required to extract, process, deliver, and install the materials needed to construct a building,” according to Mike Jackson, writing in a 2005 issue of the Springfield, Illinois–based Association for Preservation Technology International’s APT Bulletin. This is distinguished from operational energy, which is the sum of all the energy required for heating, cooling, lighting, mechanical operations, and other ongoing functions.

When one is analyzing whether a particular project is environmentally friendly, embodied energy is frequently overlooked. On many a project, more energy is expended demolishing and replacing an old building with a new, high-performance structure than is saved through increased operational energy efficiency over the life of the new building. In other words, it may take more energy to replace an older structure with a new, green one than is saved over time due to increased energy efficiency.

The majority of embodied energy analyses are based on Energy Use for Building Construction, a study conducted in 1976 that calculated the embodied energy contained in common building materials. Most recent analyses use these older numbers to contextualize and analyze modern building practices. Over the years, the underlying embodied energy figures of various raw materials have certainly changed as raw materials producers and manufacturers have become more efficient. At the same time, though, building products are becoming more technologically advanced and more highly refined, both of which increase embodied energy.

The calculation of a structure’s embodied energy starts with the energy expended to source raw materials, such as stone, wood, iron, and copper. Embodied energy is then added during processing, as when trees are milled into usable lumber, or iron ore processed into steel. The energy used to transport the materials to the building site is added to the calculation, as is the energy used to assemble the materials into a structure.

During a building’s operational life, additional embodied energy may be added in the form of repairs and replacements; for instance, replacing a roof adds more embodied energy. The energy used to heat, cool, light, clean, and otherwise operate the building on a day-to-day basis, however, is considered operational rather than embodied energy.

As Figure 1 shows, half of an office building’s embodied energy is contained in the materials used for the building envelope and structure. Ironically, the materials common to many older buildings have much lower embodied energies than those typical of newer construction. Stone, wood, and brick are the primary structural elements of premodern structures and they have some of the lowest embodied energy of any materials used. Conversely, new buildings rely heavily on steel, aluminum, and glass, materials with significantly higher embodied energies.

For any energy savings to be realized by new construction, the energy saved through increased operational energy efficiency must exceed all of the energy expended in developing the new building. In simplistic terms, if the sum of annual operational energy savings over the useful life of the new structure is less than the embodied energy of the new building plus the energy used to tear down the old one, then it makes sense to rehabilitate the old structure; otherwise, build new.

While research in the area is scant, estimates of the ratio of embodied energy to operational energy used by a building over its lifetime range from 5:1 to 30:1. The ratio itself does not mean that the environmental payback period can exceed 30 years; we get those numbers by plugging in data—operational energy savings times (five to 30) weighed against the embodied energy of the new buildings.

This equation only takes into account the comparison of the embodied energy used to build the new building and demolish the old one. Somehow, though, it seems inappropriate to simply discard the energy embodied in a functional older structure, especially at a time when constraints on energy and resources are increasingly apparent, unless doing so will produce a significant savings in energy use and other major benefits. Nevertheless, the loss of the old embodied energy is seldom considered in determining the environmental benefits of a new building; it is simply dismissed as a “sunk” cost.

The LEED-NC Bias

The savings in energy use that can be achieved by reusing older buildings, along with the other benefits of rehabilitation, argue for a careful evaluation of an older structure before demolishing it. There certainly will be many times when it will be preferable to build new, especially until the technology and economics of rehabilitating older buildings improve. That said, there also will be many times when rebuilding and reusing an older structure will be the clear environmental choice.

The USGBC’s Leadership in Energy and Environmental Design (LEED) program is a method of evaluating whether a development project has been performed in ways considered friendly to the environment. The LEED program for both new construction and major rehabilitations are combined in LEED-NC. In the past few years, it has become the system most developers interested in developing green (a rapidly growing segment of the industry) use to guide their environmental decision-making.

The LEED program allows developers to accrue points for environmentally sound practices—different levels of certification are available depending on the number of points a project accumulates. The points available under the LEED-NC program cover a variety of issues ranging from site selection, energy usage, waste disposal, and recycling, to landscaping and materials used.

But the points available under LEED-NC for the reuse of an existing building do not appear to adequately reflect the considerable savings—especially in embodied energy—that are available from rehabilitation. For example, of the 69 points available under the program, only three are given for reusing 95 percent of the floors, walls, and roof and 50 percent of the nonstructural interior of a structure. This is a mere 12 percent of the 26 points required for minimum certification. Compare this with the ten points available for reductions in operational energy (though the percentage reductions required to get these ten points is somewhat less for rehabs than for new construction). While this is admittedly not a full analysis of the LEED-NC system, it suggests that at this point LEED-NC does not fully recognize the environmental benefits of rehabilitation.

Why Should We Care?

Why is it important for LEED-NC to adequately account for the inherent environmental advantages realized by building reuse? One reason is the signal it sends to developers.

Though only 14 years old, the USGBC is rapidly growing, with its membership tripling in the last four years. While its LEED rating system is still evolving, it is having a major and positive impact on construction in the United States; despite its newness, there are more than 500 million square feet (46.4 million sq m) participating in the system.

Indeed, LEED has become shorthand for “environmental” in real estate development circles, and the absence of LEED certification sends the message to the market that the development is not environmentally friendly. Furthermore, being “green” has taken on a cachet, and many different market actors are rushing to find ways to signal that they, too, are green.

The result is that the USGBC has created a powerful market signal on the best ways to develop green. If LEED-NC is wrongly skewed to new development, it sends an unfortunate signal. Were it properly calibrated to account for the inherent benefits in building reuse, it could encourage developers seeking the “green” label to more carefully consider reusing buildings.

Similarly, local governments are turning to LEED standards when they create incentives for environmentally responsible development. Governmental adoption of LEED standards amplifies the signals LEED certification sends by tying tangible benefits to certification. If building reuse projects do not get the LEED recognition they deserve, they will not get the governmental incentives they also deserve, such as tax credits and accelerated permitting.

Some Suggestions

If there is indeed an imbalance in the LEED-NC program, there are several options to correct it. The USGBC could create a LEED program specifically for rehabilitating buildings—a LEED-R program, for instance—much as it has been suggested that a LEED-HB program be created for historic structures.

This, however, may not be the most effective way to encourage the reuse of existing buildings. By keeping rehab and new construction projects under one umbrella, LEED-NC may better encourage developers to compare these two alternatives side by side.

Instead, it would be preferable for the LEED-NC standard to be modified to better account for the inherent environmental benefits realized by building reuse. In particular, consideration should be given to changing the balance between embodied energy and operational energy in the points made available under the program. While the energy embodied in a new structure may be harder to calculate precisely than its operational energy savings, it may be possible, for instance, to develop simple proxies for the embodied energy that can be compared with the projected operational energy savings.

LEED aside, there are many other areas where work is needed to encourage and support the reuse of more existing buildings and, at the same time, increase their energy savings and sustainability. Among these are improving and expanding the use of the new “smart” codes for rehabilitation that do not require rehabilitated structures to meet the same criteria as new construction.

New technologies and new ways of analyzing how buildings are heated, cooled, and lighted are necessary. Some are just becoming available, and work is needed to move these new products and processes into the market and to test their economics.

In many instances, economic incentives are misaligned and new ways are needed to share the economic benefits of energy-saving retrofits. For example, a building owner has little incentive to invest in energy-saving changes when his or her tenants are the ones paying the utility bills and thus getting all the financial savings.

Remember that if half of the space that will exist in 2030 has yet to be constructed, half of it already exists. How we use and reuse this existing space will affect the environment and our overall energy use as much as everything we build new in the years to come. This means that we need to look carefully at the how the choice is made to tear down an existing building and replace it with a new one. And as we face the potential demolition of 82 billion square feet (7.6 billion sq m) of space over the next 20 years, we need developers to make the right choices if sustainability is important to us.

In short, the rehabilitation and reuse of older structures is a new and wide open field. The potential environmental benefits are enormous, as are the possible financial benefits. To date, it has simply not received the attention it deserves.

John McIlwain is a ULI senior resident fellow and holds the ULI/J. Ronald Terwilliger Chair for Housing. Knox McIlwain is a student at the New York University School of Law and editor-in-chief of the NYU Journal of Legislation and Public Policy.

The Hidden Cost of Window Replacement

Aside from affecting the decision of whether to demolish and rebuild or reuse a building, embodied energy analysis is relevant to renovation decisions as well. For instance, in an effort to achieve greater operational efficiencies, older wooden windows are often replaced with new aluminum ones. Note that aluminum has an embodied energy (227 MJ/kg) almost 100 times greater than that of wood (2.5 MJ/kg). Thus, the energy payback period on these replacements, which can be as high as 100 years, and the economic payback period (realized through lower energy bills due to reduced energy use) typically far exceed the projected life of the replacement windows, and certainly the warranty period, which is frequently only one or two years.

Walter Sedovic and Jill H. Gotthelf, “What Replacement Windows Can’t Replace: The Real Cost of Removing Historic Windows,” APT Bulletin, Volume 36, Number 4, 2005, page 27.