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This section addresses the special nature of historic structures and how they should be treated with respect to operations and maintenance (O&M) in the ongoing use of a structure, whatever that use may be. Modern use of historic structures inherently comes into some measure of conflict with the desire to preserve them. These conflicts may be caused by code requirements, accessibility issues, human comfort, life safety, and other modern needs which can cause conflict and require compromises. Therefore, everyone involved in the O&M of historic structures should be aware of a structure's significant and character-defining features, past treatments, and how O&M should be applied to best preserve the structure.
The term historic structure is used throughout this resource page to include not only historic buildings, but also other types of historic structures and components of cultural landscapes. While each historic structure has its unique set of needs, the principles outlined herein should generally apply. (See also WBDG Historic Preservation.)
Operating and maintaining historic structures must take into account the following factors:
- significance of features
- original and later construction components and materials
- current or future (planned) use
- treatment objectives
- technical information about appropriate O&M processes and products, and
- specialized preservation skills training
Historic Structure Reports
If available, a Historic Structure Report (HSR) will provide a summary of a structure's history and development, dating from original construction. Information would typically be gathered through documentary research, archaeological surveys; and documented through photographs and measured drawings, materials and finishes analysis, and physical inspection. The HSR further helps identify the intact significant historic and character-defining features of the structure. It usually contains a complete assessment of the condition of the structure at the time of the report and recommendations to address physical condition problems as well as recommendations to restore, preserve, rehabilitate or otherwise treat the historic and character defining features of the structure, depending on the goals set out by the Owner. Some HSR documents may contain a section that addresses O&M. Regardless, if an HSR exists, it should form the basis for O&M requirements development.
Should an HSR not exist, it is strongly recommended that one be developed before performing any extensive efforts to preserve, repair, and/or maintain the structure. An HSR should be prepared by a team of preservation professionals under the leadership of a preservation architect. The Association for Preservation Technology International is a professional membership organization of mostly architects, engineers, planners and other professionals who work extensively in the field of preservation of historic structures and landscapes, and a good resource to find such professionals. The American Institute of Architects' Historic Resources Committee is also a good source to find preservation architects and related information.
If the structure is individually listed on the National Register of Historic Places or is a National Historic Landmark, consult the nomination form that led to its listing. It will likely contain information about a structure's historical and architectural significance, and about the historic character-defining features that give it historical integrity and are important to preserve.
The Secretary of the Interior's Standards for the Treatment of Historic Properties, a set of federal guidelines, provide various levels of treatments that can be applied to historic structures and landscapes, such as reconstruction, restoration, preservation, and rehabilitation. Although no guidelines exist for O&M as a treatment category, there is much to be learned from a review of these standards for the treatment category that is most appropriate for a given structure. The treatment category is determined by the goals that the Owner has for the structure, whether for historical interpretation for the public, continued use as the original purpose for which it was built, or adaptively re-used for a different purpose. Within each treatment category there are guidelines that address issues such as protecting, maintaining, and repairing features. These will provide a strong basis for developing O&M requirements.
Maintenance of Historic Materials
Historic structures are usually made of materials that are natural, hand-crafted and were not the product of a manufacturer. Therefore, O&M information was not likely generated at the time of construction. Many of these same materials (wood, stone, brick, metal, etc.) are used in construction today, however, they may be of a different quality, durability or process of manufacture and the procedures for maintenance and repair can be quite different. For example, 18th century hand-made brick is quite different than 20th or 21st century machine-made brick. O&M procedures, products, techniques and schedules that are developed or recommended by manufacturers of modern materials should not automatically be applied to similar materials on historic structures. Preservation Briefs, published by the U.S. National Park Service, is one source of technical information about the treatment of historic materials. The briefs address many types of materials and applications, and contain information directly applicable to the development of O&M procedures.
O&M for HVAC and other Modern Building Systems in Historic Structures
Historic structures can be particularly sensitive to changes in environmental conditions brought about by modern HVAC systems. Most historic structures do not have insulation and vapor barriers commonly found in modern construction. Many have a high level of painted and other finishes that could be damaged by changes in temperature, relative humidity and visible and ultraviolet light exposure. Modern HVAC systems can compromise a historic structure due to the need of excessive cutting and patching into historic materials and finishes to conceal ducts, pipes, and equipment. The ASHRAE Handbook HVAC Applications, Chapter 23 provides guidance on system design for historic structures, museums, galleries, archives and libraries. It is recommended that an environmental monitoring program be established to obtain building performance data for at least one year prior to designing/installing a new HVAC system in a historic structure, and that the monitoring program continue after the installation to observe how the system installation is affecting the building performance. (See also WBDG Update Building Systems Appropriately.)
Once a system is installed, it is important to determine the structure's limitations relative to system O&M. A structure's use will determine the desired operating parameters, temperature, and relative humidity set points and other HVAC system considerations, i.e., whether it is conditioned for human comfort, for museum artifact collections (as in an historic house museum) or if it is generally unoccupied and used for storage of non-sensitive material. The desired operating parameters need to be weighed against the ability of the building envelope to perform and maintain operating parameters without causing damage to the building envelope and the structure. It is best to work with a preservation architect familiar with the historic construction and the engineer who designed/installed the HVAC system, to determine what operating parameters the structure can sustain without damage to the historic fabric. Compromises sometimes must be made between the desired operating parameters and the needs of the historic structure.
For museums, house museums, libraries and archives contained within historic structures, these compromises can be more difficult, based on the needs of artifacts or archival collections versus those of the historic structure. Museum and archival collections generally benefit from being in an environment with stable relative humidity and temperature levels, within a much tighter range of control than is needed for human comfort. The tensions and balance of these often conflicting needs are recorded in the New Orleans Charter for the Joint Preservation of Historic Structures and Artifacts, jointly issued by the Association for Preservation Technology International and the American Institute for Conservation. The Charter provides a set of governing principles that strike a balance between the needs of artifacts and historic structures that house them. The art conservation profession has developed widely accepted standards for appropriate environmental conditions for artifact and archival collections in order to ensure long-term preservation of the artifacts and archival documents. The American Institute for Conservation of Historic and Artistic Works is the professional organization for conservators and can help provide guidance on appropriate environmental parameters depending on the type of artifacts or documents involved.
Once safe operating parameters are established, it is important to train not only the facilities management and O&M staff, but also the owner and occupants of the structure so they understand the limitations of the historic structure and its HVAC system and do not adjust temperature and/or relative humidity set points outside the range that is established as "safe" for the structure.
Scheduled preventive maintenance of the HVAC system installed in a historic structure is as important as it is for any system. For systems that have water distribution piping, consider installing drip pans with leak detection devices that are wired to a building automation or security system. In this way, the O&M staff will be alerted quickly if there is a system leak or pipe break, thus preventing or minimizing damage to historic building materials and finishes.
Keeping old equipment running while contemplating the impact of installing new more efficient equipment is a unique and complex issue to balance. Further, cleaning of delicate surfaces and artwork require the use of products that are less likely to damage these surfaces, while providing a healthy environment for the building's occupants. Maintaining strict temperature and humidity control to protect artwork and antiquities is an additional challenge for the operations and maintenance staff. Extensive research has been done by the Smithsonian Institution regarding the effect of temperature and humidity on artifacts and can be found in the following links:
Determining the Acceptable Ranges of Relative Humidity and Temperature in Museums and Galleries: Part 1 and Part 2
Specialized Skills Training for Maintenance and Building Trades Personnel
Generally, most individuals in the building trades, when faced with maintaining and preserving an historic structure, do not have the necessary specialized skills and knowledge, but rely on their knowledge of modern construction practice. However, the repair, maintenance and preservation of historic structures often requires specialized sets of skills and knowledge about the proper methods and treatment of materials and details of construction. The availability of individuals who have the expertise is far less today than when the structure was erected. However, it is strongly recommended that the Owner of an historic structure seek out those individuals when working on a historic structure.
Training programs, somewhat limited in the United States, offer short courses, workshops and more extended degree or certificate programs. One resource is the Preservation Trades Network (PTN), a non-profit membership organization founded to provide education, networking and outreach for preservation and traditional building trades. PTN sponsors an annual International Preservation Trades Workshop and other programs. It has a network of members who specialize in the preservation and traditional trades. The Preservation Directory, PreserveNet and PTN list preservation education programs as well as many other useful resources.
Care and Cleaning of Historic Materials and Finishes
Historic materials and finishes generally require that more than the usual amount of caution be exercised when selecting cleaning products, use of mechanical cleaning equipment, and cleaning methods and frequency. To date, little has been published about this topic, and at best it is difficult to find. Three guiding principles that should be used when developing care and cleaning practices for O&M of an historic structure are as follows:
Use the gentlest means possible and the gentlest products possible in cleaning historic materials so as not to damage an underlying finish or substrate. Locate as much information as possible about recommended care and cleaning products and applications before making a selection.
Test all cleaning products and methods in a location that is least noticeable. Evaluate the results to see how effective the products and methods are. Visually inspect for adverse effects or damage resulting from the cleaning. Document the conditions before and after the testing by taking photographs and notes.
After selecting an effective non-damaging cleaning process and product, record the information about the testing process, results, product(s) used, methods/procedures and cleaning schedule in an O&M manual. Thoroughly train everyone involved in cleaning to ensure they understand not only the products and procedures to be used, but the underlying reasons for not using any others. It may initially be difficult to determine the best frequency of cleaning, but by routinely monitoring the effectiveness of the product(s) and procedure used, experience will be gained over time. If necessary, cleaning schedules should then be adjusted to take into account the patterns of use of the structure and general wear of the materials.
Developing an O&M Manual for Historic Structures
The process of developing an O&M Manual is quite different for historic structures than for modern structures. Most modern structures are a set of manufactured parts that are assembled mostly in the field with standard construction details that are well documented through as-built contract documents. Much of the O&M information is readily available from product manufacturers and typically assembled by construction contractors. Historic structures will usually require research, testing, physical inspection and specialized knowledge and skills to assemble and prepare customized information to meet a structure's preservation needs while maintaining its operating use.
It is highly recommended that a team be assembled that includes at a minimum, a preservation architect and a preservation trades person who have the specialized knowledge and skills for working with historic structures to guide content development for an O&M Manual. This team may also be able to provide training to the owner's employees or contractors who regularly maintain the structure.
The following process can be applied when developing an O&M Manual for a historic structure:
- Review available documentation (e.g., HSR, materials and finishes analysis reports, integrated pest management plans, archaeological reports, and other studies).
- Research to fill in the gaps of knowledge (especially if there is no HSR or other substantial research documentation reports).
- Identify the historic character defining features of the structure that contribute to its historic integrity and that are important to preserve (consult National Register nomination, HSR or other documents if they exist).
- Determine the current or proposed use of the structure and the Owner's desired treatment approach (reconstruction, restoration, preservation or rehabilitation).
- Assess the condition of all elements of the structure, identify causes of deterioration or other problems and prioritize treatments for both corrective and preventive maintenance. It is recommended that an annual inspection program be established to re-evaluate and update conditions, recorded procedures, products, etc.
- Use the Standards and the Preservation Briefs as guides to develop specific O&M treatment approaches to various features and materials used in the structure for both corrective and preventive maintenance.
- Test corrective and preventive maintenance treatments whenever possible prior to work to establish the gentlest or least intrusive treatments possible to maintain each material, finish or feature.
- Record and document all corrective and preventive maintenance treatments so that results can be later assessed and used to inform future treatments. Include photographs, notes, test reports, observations and any other relevant information.
Applying information technology in maintenance management through the use of facility management databases. Commercially available, they range from "off the shelf" to proprietary customizable software that address facility management in a fairly generic way. These tend to deal well with more modern facilities but most do not take into account the special needs and issues concerning historic structures. Some larger organizations that manage a significant number of historic structures have been able to invest in customized software for this purpose. Some providers are starting to develop more specialized applications for this niche market in facilities management.
The need for more specialized training in preservation trades technology. Few programs exist in the United States that focus on preservation trades training. However, more programs are under development in the form of post-secondary courses and degree programs as well as less traditional short courses and workshops that are marketed to incumbent workers. The International Trades Education Initiative was created by the Preservation Trades Network to focus more attention on the creation of preservation trades training opportunities. They organize a symposium on this topic every two years.
Relevant Codes and Standards
- ASHRAE Handbook HVAC Applications, Chapter 23, Museums, Galleries, Archives, and Libraries
- International Existing Building Code
- The Secretary of the Interior's Standards for the Treatment of Historic Properties, National Park Service, Technical Preservation Services
Organizations and Resources
- Association for Preservation Technology International
- Building Technology Heritage Library Internet Archive
- Heritage Preservation Services Bookstore, National Park Services, Technical Preservation Services
- National Trust for Historic Preservation
- New Orleans Charter for the Joint Preservation of Historic Structures and Artifacts
- Preservation Briefs, National Park Services, Technical Preservation Services.
- Preservation Trades Network
- >The American Institute of Architects Historic Resources Committee
- The American Institute for Conservation of Historic and Artistic Works
- The Preservation Directory
- The Old House Journal
- The Secretary of the Interior's Standards for the Treatment of Historic Properties, National Park Service, Technical Preservation Services
- Traditional Building
- Building Maintenance and Preservation: A Guide to Design and Management by Mills, Edward. Oxford: Reed Educational and Professional Publishing, 1996.
- Caring for Your Historic House by Heritage Preservation and National Park Service. New York: Harry N. Abrams, 1998.
- Conservation of Historic Buildings, 3rd Edition by Feilden, Bernard Melchior. Architectural Press, 2003.
- Cyclical Maintenance for Historic Buildings by Chambers, Henry. Washington, DC: National Park Service, 1976.
- Historic Building Façades: The Manual for Maintenance and Rehabilitation by Foulks, William, and New York Landmarks Conservancy, New York: John Wiley & Sons/Preservation Press, 1997.
- Historic House Museums: A Practical Handbook for Their Care, Preservation, & Management by Butcher-Younghans, Sherry. New York: Oxford University Press, 1993.
- Historic Preservation Technology: A Primer by Young, Robert A. New York: John Wiley & Sons, 2008.
- Housekeeping for Historic Homes and House Museums by Heaver, Melissa, Washington, DC: National Trust for Historic Preservation, 2000.
- Maintenance Programming Manual for Historic Buildings by Leeke, John. Augusta, ME: Maine Historic Preservation Commission, 1990.
- Preventive Maintenance for Historic Buildings, a CD-ROM training program for small museums by Goodall, Harrison. Conservation Services, Langley, WA. firstname.lastname@example.org
- "Tensions and Omissions in Maintenance Management Advice for Historic Buildings" in Structural Survey, Vol. 22, Issue 3 by Dann, Nigel and Wood, Sue. Emerald Group Publishing, Ltd., 2004.
- "The Digital Age" in Traditional Building Magazine by Pepi, Raymond. Restore Media, August 2007.
The American Association for State and Local History has a number of publications that may be useful in O&M for historic structure:
- Technical Report #3 Basic Principles for Controlling Environmental Conditions in Historical Agencies and Museums, American Association for State and Local History.
- Technical Leaflet 181 Wood Floor Management (Downloadable copy)
- Technical Leaflet 183 Disaster Planning for Cultural Institutions (Downloadable copy)
- Technical Leaflet 206 Protecting Cultural Heritage Properties from Fire (Downloadable copy)
- Technical Leaflet 234 Disaster Planning, Preparedness, and Recovery (Downloadable Copy)