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Greening Historic Buildings
Already efficient because of their embodied energy and construction, historic buildings can become even more energy efficient with the careful addition of new technology.
Historic buildings have an inherent environmental benefit because they already exist and often have attributes that are smart passive strategies for low operating costs. Every building, however, can take advantage of new technologies, systems and materials to further reduce environmental impacts.
Existing buildings represent already expended energy, water and carbon. Reusing the intact building is the most effective way to capitalize on this and avoid the environmental impacts of new construction. Recycling demolished building materials only captures a limited amount of the existing resource. Donovan Rypkema estimates that the demolition of 10,000 square feet of old building wipes out the environmental benefit of recycling 2,688,000 aluminum cans. Yet the importance of resource conservation and reuse as a strategy has not yet permeated the green community. Under the old LEED-NC metric system, the building reuse credits were the least used of all achievable points.
Many historic buildings have the very attributes that are pursued or should be pursued in new construction to create a sustainable society. These include urban density, transit access, building form and massing that utilize natural daylighting and ventilation, use of local and durable materials, and a connection to community.
Historic tax credits, which have stimulated the reuse of over 34,000 buildings and investment of over $43 billion, may be the greenest legislation ever created. Not only have the environmental impacts of new construction been avoided, but most of these buildings are urban and almost half created new urban housing which, according to the Urban Land Institute, reduces vehicle miles driven by 38 percent per household. The U.S. transportation sector emits more carbon dioxide than all sources combined in every other country except China and, according to the Environmental Protection Agency, driving a private car is probably a typical citizen’s most polluting daily activity.
Green attributes and green location are important, but more must and can be done to reduce the significant contribution that all buildings, including historic, make to climate change. An holistic approach to design seeks opportunities that work with the building. For instance, what is the potential for stormwater management, natural building ventilation, seasonal shading, solar gain and biophilia delight? Does the site or the building offer opportunities for renewable energy? What are the building’s natural assets: high thermal mass for the fly wheel effect; natural but lost ventilation systems; daylighting; a basement big enough for energy storage systems; an attic adequate for heat recovery; and/or flat roof areas for solar hot water, photovoltaics and green roof systems? Are the existing materials durable and low maintenance? Are proposed new green materials healthy, durable and easy to clean?
New green materials should be reviewed with consideration to the full cycle of extraction, production, service life and disposal. Each of these stages has environmental impacts and contributes to resource depletion, water and energy consumption, waste production and air emissions. Unfortunately, all that is called green may not be green and as historians know only too well, the miracle products of one age, such as asbestos, lead paint and pcb laden caulks, are often the problems of the next.
The stewardship of historic buildings, first and foremost, requires that we do no harm in safeguarding our physical heritage. Depending on use, new products should be incorporated with caution, and considerations beyond material source are essential. The repairability of many existing materials, like wood windows or masonry construction, is possibly the greenest attribute of all since repair extends service life. Doubling the life of a product (or a building) halves the environmental impact of its fabrication.
Direct Energy Use
The focus of green is often on the reduction of direct energy use in a building and rightly so since buildings use 40 percent of the energy produced in the United States. Calculations for energy use typically are in terms of units of energy used per square foot of building. This metric neglects issues of user density and implies that a new building with a lower square foot of energy use is an improvement over an existing building with a higher use.
This is not necessarily the case. When considered in terms of total use, a small house built to only moderate energy performance standards uses substantially less energy for heating and cooling than a large house built to very high energy performance standards. Living area per family member has increased by a factor of three since the 1950s and smaller, older homes that have a higher occupant density are now frequently the victims of the tear down trend, even though they are better for the environment than new large homes that require exponentially more construction materials, cover more of the site – causing more storm water runoff – and often use more total energy.
Occupant density in historic institutional and commercial structures is also a strategy for reducing environmental impacts since better utilization of existing spaces and renovations of attics and basements can increase the number of people using a building. When making renovations, capturing opportunities for introducing natural light are important, because artificial lighting contributes heat, which increases cooling loads and uses a significant amount of electricity. Electricity in the United States comes mostly from coal-fired plants, which are responsible for 30 percent of the country’s total greenhouse gas emissions. Reducing cooling and lighting loads addresses the majority of electricity used in buildings.
Cooling is just one part of the mechanical systems of a building. The design and operation of these systems are at the heart of all energy reduction strategies. The objective of mechanical system design is to provide heating, ventilation and air conditioning while controlling temperature and humidity. The goal is to accomplish this with the least amount of energy while holding the first costs to a minimum.
Many older buildings have inefficient steam boilers that are large, wrapped in asbestos and difficult to remove. They often vent through crumbling chimneys. Replacement offers the opportunity to utilize highly efficient modular condensing boilers that can fit through standard doors and are sidewall vented. Limited space in ceiling cavities and walls often leads to a decision to utilize the more efficient heat transfer capacity of water rather than air. The same space restrictions have led to increasing installations of ground-source heat pumps, which eliminate the need for a cooling tower and when used for heating, require no vent at all. A ground-source heat pump either collects heat from the ground or collects heat from the systems and rejects it to the ground with either vertical "wells" or a horizontal loop system.
Project teams can utilize tools such as energy modeling and air infiltration testing to create and compare alternative scenarios for performance criteria. A full decision matrix includes weighting of multiple issues such as energy use, acoustics, LEED points, controls, aesthetics, first cost, life-cycle cost, funding sources, installation pragmatics, durability, repairability, maintenance, comfort and even public relations. Facilitating this decision process for numerous stakeholders provides an organized approach to balancing what may be conflicting goals and creates a project record of how and why decisions were reached.
Early Design Decisions
Identifying options and implications early in the design process is possible with the full involvement of a smart integrated team that can quickly assess the unique opportunities that each project offers. A knowledgeable team seeks tried and true solutions while exploring out-of-the-box opportunities that may spring from new products, data and information. In the most successful rehabilitations, old and new learn from each other.
For instance, an existing building at the University of Virginia has an unusually long, unprotected southern exposure. The design team is exploring, through energy modeling and visual simulation, the effect of window awnings, which were once routinely installed on buildings such as the Massachusetts State House and can be mounted to avoid building damage. However, the awnings being considered are a photo-voltaic shading system that link directly to an LED light fixture in the office behind each window. The awning industry claims that traditional awnings can reduce heat gain by 65 percent. Photovoltaic awnings accomplish this while also creating energy.
Learning from, and recovering the past is often a part of working on historic buildings. Systems for ventilation, whether cables linked to roof hatches in 19th-century churches or double-hung windows and transoms, have often become inoperable and changes have been made that preclude buildings from functioning as originally designed. Elaine Gallagher Adams, an architect with the Rocky Mountain Institute, tells a story about a 19th-century courthouse designed with high ceilings, operable windows and awnings.
Over time, the awnings deteriorated and were removed. Central air conditioning was installed to compensate for the solar heat gain. The air condition ducting required lowering the ceilings, blocking the ventilating transoms and the upper part of the windows. The top part of the double-hung windows was fixed, no longer allowing the air to circulate in at the bottom and out at the top, even if the windows were used. More ceiling lights were added because of the loss of daylight from the lowered ceiling, which increased the heat gain, which increased the cooling requirements. All of this, combined with an inefficient boiler system, helped to contribute to the myth that historic buildings are poor energy performers. The documentation shows otherwise.
According to the U.S. Department of Energy, the energy intensity of buildings constructed before 1960 is lower than post 1960, and the utility costs for historic federal buildings are 27 percent less than non-historic. A study by the British Ministry of Justice found that pre-1900 buildings are the most energy efficient per square meter and in the use of space. The same study found that occupants of historic buildings were more tolerant of minor inconveniences, which was attributed to the high quality of the work spaces.
John Muir, the founder of the Sierra Club, said in 1911, "When we try to pick out anything by itself, we find it hitched to everything else in the Universe." Greening strategies should recognize this. For instance, water and energy are tightly linked – massive amounts of energy are used to clean and transport water and waste and massive amounts of water are used to create energy. Over 52 percent of the fresh surface water withdrawals in the United States are for the cooling required in thermal power plants. Reducing energy use reduces water consumption and vice versa.
The installation of water saving fixtures is one of the simplest strategies available to property owners to lower water consumption. A new low-flow or dual-flush toilet uses 75 percent less water than an old toilet. Aerated faucets and showerheads are equally effective. Capturing water from sinks and showers for use in toilet flushing is possible with new products that are either whole building or single bath. Water leakage often goes unnoticed, but may account for 10 percent of a water bill.
Holistic thinking is a mandate for achieving environmental sustainability and the same mandate celebrates the aspects of historic buildings and heritage that contribute to social well-being and full sustainability. Sustainability ensures communities in which all are safe and happy with a sense of orientation and connectivity that heritage contributes to by ensuring the uniqueness of each place.
The famous quote from the 1987 report by The World Commission on Environment and Development defines sustainability as "development that meets the needs of the present without compromising the ability of future generations to meet their own needs." Historic buildings, the embodiment of past events and social decisions, are an irreplaceable resource that must be sustained for the benefit of people in both the present and the future. Increased awareness and opportunities for environmental sustainability are an exciting new opportunity in the practice of historic preservation, which has always been about stewardship and the careful management of change while respecting and protecting the past. TB
This article is extrapolated from a presentation at the Traditional Building Conference in the spring of 2009 by Jean Carroon of Goody Clancy and Tom Perry of Shawmut Design & Construction. Jean Carroon, FAIA, LEED AP, is the Principal for Preservation at Goody Clancy, a Boston design firm of 100 architects, planners, urban designers and conservators. Nationally recognized for her achievements in the field of sustainable design for historic buildings, she is a member of the National Trust for Historic Preservation Sustainability Coalition, Boston Mayor Menino’s Green Building Task Force, and one of the founders of the Technical Committee on Sustainable Preservation with the Association of Preservation Technology. Her current projects include renovations for the General Services Administration, University of Virginia and the University of Michigan.
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