Rehabilitation - a form of attempting to preserve as much as possible, while being willing to make alterations to accomplish a desired goal - e.g. - to keep a covered bridge open to traffic, one will have to accept more modifications than one would have to if the bridge was not to be open to traffic.

Restoration - a form of preservation aimed at maintaining a functioning structure if possible, but it allows some strengthening, preferrably hidden, as in that done on the Capitol Dome or at Monticello. It's pretty hard to hide strengthening in a CB project, although efforts are made to do so at times.

Reconstruction - the most restrictive form of preservation, and more aimed at preserving the original fabric or examples of construction details, even if that means losing the functionality of the structure (e.g. maintaining some features of a CB may force acceptance of a non-standard capacity such that the structure could not be deemed safe for traffic).

       It is my firm conviction, that if we are to keep bridges open to traffic (and I think most of us wish to), then we cannot accomplish that following the strict requirements of a "reconstruction" project. Even "restoration" involves many actions not compatible with the work normally envisioned for CB projects. Hence, in my opinion, virtually all work with which I am familiar fits the category of rehabilitation projects and not restoration and certainly not reconstruction projects. All projects for the Vermont Agency of Transportation (VAOT) that I have been involved with has insisted on careful use of these terms to abide by the guidelines from Federal HighwayAdministration (FHWA). I am unaware of any Engineer or Owner who claims to have fulfilled work on an extant CB to maintain its use for larger vehicular traffic while meeting all of the stringent criteria of either restoration or reconstruction. Having said that, I suspect that there are those who will claim to have done so--we all would benefit from more education about this topic.

       The following was copied directly from the ACHP website, under the heading of 106 and the Secretary's Standards for Historic Preservation (http://www.achp.gov/secstnd.html#SHPP):
              Phil

The following general standards apply to all treatments undertaken on historic properties listed in the National Register.

1. Every reasonable effort shall be made to provide a compatible use for a property that requires minimal alteration of the building, structure, or site and its environment, or to use a property for its originally intended purpose.
2. The distinguishing original qualities or character of a building, structure, or site and its environment shall not be destroyed. The removal or alteration of any historic material or distinctive architectural features should be avoided when possible.
3. All buildings, structures, and sites shall be recognized as products of their own time. Alterations which have no historical basis and which seek to create an earlier appearance shall be discouraged.
4. Changes which have taken place in the course of time are evidence of the history and development of a building, structure, or site and its environment. These changes may have acquired significance in their own right, and this significance shall be recognized and respected.
5. Distinctive architectural features or examples of skilled craftsmanship which characterize a building, structure, or site shall be treated with sensitivity.
6. Deteriorated architectural features shall be repaired rather than replaced, wherever possible. In the event replacement is necessary, the new material should match the material being replaced in composition, design, color, texture, and other visual qualities. Repair or replacement of missing architectural features should be based on accurate duplications of features, substantiated by historic, physical, or pictorial evidence rather than on conjectural designs or the availability of different architectural elements from other buildings or structures.
7. The surface cleaning of structures shall be undertaken with the gentlest means possible. Sandblasting and other cleaning methods that will damage the historic building materials shall not be undertaken.
8. Every reasonable effort shall be made to protect and preserve archeological resources affected by, or adjacent to, any acquisition, stabilization, preservation, rehabilitation, restoration, or reconstruction project.

Specific Standards for Historic Preservation Projects

The following specific standards for each treatment are to be used in conjunction with the eight general standards and, in each case, begin with No. 9. For example, in evaluating acquisition projects, include the eight general standards plus the four specific standards listed under Standards for Acquisition. The specific standards differ from those published for use in Historic Preservation Fund grant-in-aid projects (36 CFR Part 68) in that they discuss more fully the treatment of archeological properties.

Standards for Acquisition

9. Careful consideration shall be given to the type and extent of property rights which are required to assure the preservation of the historic resource. The preservation objectives shall determine the exact property rights to be acquired.
10. Properties shall be acquired in fee simple when absolute ownership is required to insure their preservation.
11. The purchase of less-than-fee simple interests, such as open space or facade easements, shall be undertaken when a limited interest achieves the preservation objective.
12. Every reasonable effort shall be made to acquire sufficient property with the historic resource to protect its historical, archeological, architectural or cultural significance.

Standards for Protection

9. Before applying protective measures which are generally of a temporary nature and imply future historic preservation work, an analysis of the actual or anticipated threats to the property shall be made.
10. Protection shall safeguard the physical condition or environment of a property or archeological site from further deterioration or damage caused by weather or other natural, animal or human intrusions.
11. If any historic material or architectural features are removed, they shall be properly recorded and, if possible, stored for future study or reuse.

Standards for Stabilization

9. Stabilization shall reestablish the structural stability of a property through the reinforcement of loadbearing members or by arresting deterioration leading to structural failure. Stabilization shall also reestablish weather resistant conditions for a property.
10. Stabilization shall be accomplished in such a manner that it detracts as little as possible from the property's appearance and significance. When reinforcement is required to reestablish structural stability, such work shall be concealed wherever possible so as not to intrude upon or detract from the aesthetic and historical or archeological quality of the property, except where concealment would result in the alteration or destruction of historically or archaeologically significant material or spaces. Accurate documentation of stabilization procedures shall be kept and made available for future needs.
11. Stabilization work that will result in ground disturbance shall be preceded by sufficient archeological investigation to determine whether significant subsurface features or artifacts will be affected. Recovery, curation and documentation of archeological features and specimens shall be undertaken in accordance with appropriate professional methods and techniques.

Standards for Preservation

9. Preservation shall maintain the existing form, integrity, and materials of a building, structure, or site. Archeological sites shall be preserved undisturbed whenever feasible and practical Substantial reconstruction or restoration of lost features generally are not included in a preservation undertaking.
10. Preservation shall include techniques of arresting or retarding the deterioration of a property through a program of ongoing maintenance.
11. Use of destructive techniques, such as archeological excavation, shall be limited to providing sufficient information for research, interpretation and management needs.

Standards for Rehabilitation

9. Contemporary design for alterations and additions to existing properties shall not be discouraged when such alterations and additions do not destroy significant historic, architectural or cultural material and such design is compatible with the size, scale, color, material and character of the property, neighborhood, or environment.
10. Wherever possible, new additions or alterations to structures shall be done in such a manner that if such additions or alterations were to be removed in the future, the essential form and integrity of the structure would be unimpaired.

Standards for Restoration

9. Every reasonable effort shall be made to use a property for its originally intended purpose or to provide a compatible use that will require minimum alteration to the property and its environment.
10. Reinforcement required for structural stability or the installation of protective or code required mechanical systems shall be concealed wherever possible so as not to intrude or detract from the property's aesthetic and historical qualities, except where concealment would result in the alteration or destruction of historically significant materials or spaces.
11. Restoration work such as the demolition of non-contributing additions that will result in ground or structural disturbance shall be preceded by sufficient archeological investigation to determine whether significant subsurface or structural features or artifacts will be affected. Recovery, curation and documentation of archeological features and specimens shall be undertaken in accordance with appropriate professional methods and techniques.

Standards for Reconstruction

9. Reconstruction of a part or all of a property shall be undertaken only when such work is essential to reproduce a significant missing feature in a historic district or scene, and when a contemporary design solution is not acceptable. Reconstruction of archeological sites generally is not appropriate.
10. Reconstruction of all or a part of a historic property shall be appropriate when the reconstruction is essential for understanding and interpreting the value of a historic district, or when no other building, structure, object, or landscape feature with the same associative value has survived and sufficient historical or archeological documentation exists to insure an accurate reproduction of the original.
11. The reproduction of missing elements accomplished with new materials shall duplicate the composition, design, color, texture, and other visual qualities of the missing element. Reconstruction of missing architectural or archeological features shall be based upon accurate duplication of original features substantiated by physical or documentary evidence rather than upon conjectural designs or the availability of different architectural features from other buildings.
12. Reconstruction of a building or structure on an original site shall be preceded by a thorough archeological investigation to locate and identify all subsurface features and artifacts. Recovery, curation and documentation of archeological features and specimens shall be undertaken in accordance with professional methods and techniques.
13. Reconstruction shall include measures to preserve any remaining original fabric, including foundations, subsurface, and ancillary elements. The reconstruction of missing elements and features shall be done in such a manner that the essential form and integrity of the original surviving features are unimpaired.

¹ Phil Pierce was selected by the Federal Highway Administration to be Principle Investigator for a research project to prepare a Covered Bridge Manual to be published by the Federal Government.