Today's energy-conscious economy means that owners of aging and historic buildings are grappling with the costs of sustainability and rehabilitation vs. new construction. Considerations often include:
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The financial and energy ramifications of demolition.
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An evaluation of potential longevity and building life-cycle.
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The social, political, or architectural significance of the buildings.
Determining the value of rehabilitation, maintenance costs, and overall energy benefits requires a process that provides a comprehensive appraisal of the building. In fact, a formula is required to quantify the known and unknown conditions particular to a building's embodied energy.
Understanding the relationship between embodied energy and historic preservation (and how they can benefit each other) at the inception of a project can save money on your existing project or leave money for your next one.
Embodied Energy vs. Operating Energy
Embodied energy is the amount of labor and energy consumed in the production of a building, from the harvesting of natural resources to the fabrication and delivery of materials to the installation of these materials and products. At the other end of the building spectrum, it includes the energy to demolish and remove building components. Embodied energy is a cradle-to-grave view. Conversely, operating energy can be easily measured—it includes the energy for HVAC, lighting, equipment, and appliances.
The balance between embodied and operating energy often involves whether you choose to retain the original exterior walls, roofs, and windows of an older building. This is a dilemma, especially concerning structures that were designed in the heyday of modern architecture, when conservation and energy use were not issues, and concrete, steel, and glass were the materials du jour. It's expensive to heat and cool an early glass building, but if you tear it down, you lose the investment in embodied energy and, possibly, historical significance.
Before an owner can decide how he/she intends to modify the building, the amount of embodied energy, balanced with the structure's operating energy—in other words, long-term costs and authenticity of material, balanced with daily costs to run the facility—should be assessed.
Measuring Embodied Energy
The Washington, D.C.-based American Institute of Architects estimates that 75 percent of public buildings in use today will be ready for renovation by 2030. Of this percentage, the majority of existing public buildings have an anticipated lifespan of 50 to 100 years. Research indicates that embodied energy is as high as 10 to 15 percent of the energy used in the 100-year lifespan of a building, with this percentage decreasing as the building ages. Calculated with a life-cycle assessment scale, data on building systems and materials are being collected throughout the world. From multiple regions and resources, the Merrickville, ON-based Athena Institute has created measurement tools that estimate demolition and disposal costs of walls, roofs, windows, floors, and structural systems. These numbers are critical in assigning value to a building's embodied energy.
To fully understand the ramifications of rehabilitation and the impact on embodied energy, include life-cycle assessments of building systems, such as mechanical, electrical, plumbing, and fire protection, as well as assessment of the building envelope, including exterior wall systems, windows, structure, and roofing. Often, the cost and impact of demolition are overlooked in total demolition for a completely new structure and partial demolition for rehabilitation. Partial and total demolition expenditures also need to be included in the equation, including equipment, energy, and landfill costs.
Old Buildings Defined
In addition to embodied energy considerations, evaluate your existing building before you ponder demolition vs. renovation. In the case of a historic structure, determine its significance, integrity, and context.
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Historic significance is the importance of a site to noteworthy events, people, or periods.
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Historic integrity speaks to the authenticity of a building or site identity (i.e. physical material remaining from a period of significance).
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Historic context sets the scene for the building or site based on events and trends.
These principles will also help determine the embodied energy contained in historic buildings. If the building is on the National Register of Historic Places, then the principles have already been addressed.
Ways of modifying existing buildings permit a range of flexibility and change.
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Preservation sustains the existing form, integrity, and materials of a historic property.
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Restoration accurately depicts the form, features, and character of a property as it appeared at a particular time by removing features from other periods and reconstructing missing features.
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Rehabilitation creates a compatible use for a property through repair, alterations, and additions while preserving the features that convey historical, cultural, or architectural values.
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Reuse retains the majority of a structure, but redesigns it for a new use.
Rehabilitation and reuse allow for more flexibility, but the owner must find a balance between significant features and maintaining a profitable and viable building. Fortunately, many jurisdictions provide tax credits to encourage the continued use of old buildings.
Not Made Like that Anymore
Evaluating an existing building for reuse can be a complex balance of opposing values. Retaining existing building elements can save money, and the quality of the original materials may exceed current industry standards. Often, the elements that define the significance of a building are the components that ensure the highest embodied energy.
For example, wood-window systems may have a low embodied energy value, but also a low operational cost because they're inexpensive to maintain and require minimal modification to meet current codes. Concrete and steel structures, on the other hand, have a high level of embodied energy and can be evaluated for durability and possible new uses. Seismic bracing is often a sizeable cost required for the continued use of historic structures, but this impact can be balanced with the initial energy and estimated lifespan of the structural members if the building has been properly maintained and hasn't suffered traumatic damage. High levels of embodied energy allow you to gain continued life from initial construction. Establishing a cost-benefit timeframe that measures demolition and rehabilitation will tell you what you need to know.
Basic Questions for Appraisals
Assessments of an aging or historic building should measure durability, integrity, adaptability, and flexibility. The flexibility of use can extend the life of a space dramatically and is, therefore, important to measure. More specifically, assessments should:
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Establish a cost-benefit timeframe to ensure accurate comparisons and a valid solution. This includes the assessment of continued life or function remaining vis-à-vis the cost of repair and maintenance.
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Verify the physical condition of the structure, building-envelope systems, and the character-defining features to be retained if the building is historically significant. The solution should be tested for flexibility to ensure an extended lifespan.
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Review the operating cost requirements because they are a significant contributor to the continued viability of a building and a sustainable solution.
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Establish a synchronized review that includes not only the physical condition, but also considers historical significance, authenticity, and regulatory requirements, such as applicable building codes and standards.
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Evaluate the effort to repair building systems, which is required to understand the scope of the project and to evaluate the life-cycle of the materials.
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Quantify the range from complete demolition to partial demolition. This is critical to understanding the total project cost and impact on the existing structure.
Gretchen K Pfaehler is director of historic preservation at Washington, D.C.-based EwingCole. She serves on the board of directors for the Springfield, IL-based Association for Preservation Technology Intl. and is an associate member of the Washington, D.C.-based American Institute for Conservation of Historic & Artistic Works.
